Watt Hours; Calculating E-bike Range

August 1, 2012

Watt hours is a way to measure the energy capacity of a battery pack, so you know what to expect from your new E-bike in terms of range performance. To calculate the watt hours (WH) of a battery pack, simply multiply the voltage by the amp hours (Ah) of the pack. A 36-volt 10-Ah battery pack has 360 watt hours. If you are nitty with your energy usage, each mile you travel will cost you about 20 watt hours. Therefore a 360 watt hour pack will get you 18 miles. The range can vary widely depending on where and how you ride.

Watt hours determine the range of your bike, the cost of your bike, and the weight of your bike….three very important factors to consider when buying  an electric bike.

Batteries come in different cell qualities. Name brand cells such as Samsung, Panasonic and A123 will last longer (number of charge cycles)  than no-name Chinese cells. Of course if your pack consists of name brand cells, the cost per watt hour will be much higher.

You want to throw that salesman for a loop? Ask him what brand and what chemistry is in the cells that the battery pack uses. If he can’t answer that, speak to someone else…or do your own research online.

A 250 watt motor will burn 250 watt hours in an hour and will last you an hour and 20 minutes at full throttle on those 360 watt hours, but it will not provide you with very much assist.

A 500 watt motor will burn through the same pack at full throttle in less than 45 minutes, but you will be given twice as much assist as you get from the 250 watt motor. If you are nitty with your 500 watt motor and run it at half throttle (250 watts) and pedal a lot, you will get the same efficiency as you get with a 250 watt motor. However the exhilaration of  available electric power is sometimes hard to resist.

Just for practice, lets count the watt hours of some of the bikes  that have been reviewed on The larger the watt hours the longer the range, the more expensive the bike, and also the heavier the bike.  So we will also list the weight of the E-bike, the price of the E-bike, and the quality of the cells.

We will list the range that the E-bike company claims, and then use our “20 watt hours per mile” standard to come up with an EB estimated real life range. In our experience most riders will be less efficient  than 20 watts per mile (its hard to lay low on the throttle), so this is a generous figure. If you are getting better than 20 watts per mile (the lower number the better) you are a real electric juice miser, or an athletic pedaler, and are probably moving at just a little fast than regular bicycle speeds.

Faraday Porteur

  • Faraday Porteur (read story)
  • $3500 (Kickstarter price)
  • 110 watt hours (really puny)
  • Claimed range: 10-15 miles
  • EB “Real Life” range: 5.5 miles
  • Weight: 39 Pounds
  • Motor: 250 watt front hub motor
  • Battery cells: A123 18650 cells LiFePO4
  • Battery life expectancy: 1000 charges
  • 2 year warranty on battery (damn good)
  • Replacement pack price $700

As you will see, compared to the other bikes on this list, this bike has a puny battery pack, especially considering its relatively high cost. It does have light weight however. This is the lightest, most stealthy looking bike on this list.  However as you will see, a mid-drive bike like the Focus Jarifa, has 4X the battery at about the same price, and its only 6 pounds heavier.


Currie Ezip Trailz

  • Currie Ezip Trailz (read review)
  • $500 (shipped!!!)
  • 24V X 10-Ah =  240 watt hours
  • Claimed range: 15-22 miles
  • EB “Real Life” range: 10 miles
  • Weight: 69 pounds
  • Motor: 450 watt brushless Currie  Drive system
  • Battery cells: sealed lead acid (SLA)
  • Battery life expectancy: 100 charges
  • Battery warranty 3 months
  • Replacement/ extra  pack price $140

This bike is as cheap as you will ever find any decent E-bike. The key to this bikes low cost is that it uses lead acid chemistry and its very heavy, especially given its low watt hour rating. (the quality of lead acid cells is very dubious, and the battery will not have much of a life span if it is not meticulously cared for). Lead acid is an older technology. Be warned you will not get 240 watt hour range out of this E-bike for very long. Only when the battery pack is brand new will you get the  EB range of 10 miles.


Specialized Turbo

  • Specialized Turbo (read story)
  • $7,000
  • 36V X 9-Ah =  350 watt hours
  • Claimed range: 25 miles
  • EB “Real Life” range: 18 miles
  • Weight: 42  pounds
  • Motor: 250 watt geared hub motor
  • Battery cells: lithium polymer
  • Battery life expectancy: 600 charges
  • Battery warranty 2 years
  • Replacement / extra  pack price (unknown), has a swappable battery

This bike has a ridiculously high price ($7000) when you consider the small size of the lithium battery (350-WH). The bike is slightly more efficient than most hub motor bikes because it uses thin road bike tires.


Currie Izip Metro

  • Currie Izip Metro (review coming soon)
  • $2600
  • 36V X 10-Ah = 360 watt hours
  • Claimed range: 20-35 miles
  • EB “Real Life” range: 18 miles
  • Weight: 55 Pounds
  • Motor: 500 watt geared hub motor
  • Battery cells: Samsung 18650 cells (high quality)
  • Battery life expectancy: 500 charges
  • Battery warranty 1 year
  • Replacement Battery $600 (plus labor charge, battery is built into bike)

The Izip Metro has the rare property of having its 360 watt hours of battery built into its purpose built frame.  Many other bikes on this list happen to have this feature, the Faraday, the Stromer, the Optibike and also the Stealth Bomber. However, this is the most affordable out of those E-bikes.


Stromer Electric Bike

  • Stromer Electric Bike (read review here)
  • $3000
  • 36V X 10-Ah = 360 watt hours
  • Claimed range: 20-45  miles
  • EB “Real Life” range: 18 miles
  • Weight: 62Pounds
  • Motor: 600 watt direct drive hub motor
  • Battery cells: Samsung 18650 cells (high quality)
  • Battery life expectancy: 500 charges
  • Battery warranty: 18 months
  • replacement/extra battery  $700  (removable swapable pack)


Focus Jarifa Mid-Drive Bike


  • Focus Jarifa  (read review here)
  • $3500
  • 26V X 18-Ah   =  468 watt hours
  • Claimed range: 80 miles
  • EB “Real Life” range: 31 miles
  • Weight: 45 pounds
  • Motor: 300 watt mid drive
  • Battery cells: Panasonic 18650 cells (best quality)
  • Battery life expectancy: 500 charges
  • Battery warranty: 2 years
  • Replacement / extra battery $800 (removable, swappable pack)

300 watt mid-drive motor…this is the most efficient bike on this list, meaning it will get you further per watt hour (we estimate 15 watt hours per mile).  This bike uses Panasonic 18650 Lithium Manganese cells (LiMn) which are considered the highest quality Lithium cells in the industry.


Pedego Interceptor


  • Pedego Interceptor (read review here)
  • $2300
  • 48V X 10-Ah = 480 watt hours
  • Claimed range: 15-30 miles
  • EB “Real Life” range: 24-miles
  • Weight: 60Pounds
  • Motor: 500 watt direct drive hub motor
  • Battery cells: lithium manganese soft cells (LiMn)
  • Battery life expectancy: 500 charges
  • Battery warranty: 1 year
  • Replacement/extra battery $600 (removable, swappable pack)


  • Currie Izip Express 720 watt hour
  • Currie Izip Express (review coming soon)
  • $5000
  • 36V X 20-Ah = 720 watt hours
  • Claimed range: 45  miles
  • EB “Real Life” range: 36  miles
  • Weight: 62Pounds
  • Motor: 750 watt  mid drive
  • Battery cells: Samsung 18650 cells (high quality)
  • Battery life expectancy: 500 charges
  • Battery warranty 2 years
  • Replacement Battery $1200 (plus labor charge, battery is built into bike)




Optibike 850R

  • Optibike 850R (read review here)
  • $12,000
  • 36V X 26-Ah   =  926 watt hours
  • Claimed range: 40-80 miles
  • EB “Real Life” range: 46 miles
  • Weight: 60 pounds
  • Motor: 850 watt mid drive
  • Battery cells: Generic 18650 cells (average quality)
  • Battery life expectancy: 500  charges
  • Battery warranty (limited): 3 years
  • Battery replacement cost $2000 (plus labor charge, battery is built into bike)

The Optibike contains an amazing amount of battery given its small form factor and weight. However, its high cost is a definite downside. The replacement cost of the Optibike battery pack is a whopping $2000, and bike must be hazmat-shipped (expensive) to Boulder Colorado to replace the pack, since the battery is built into the frame. Also this makes it extremely inconvenient for warranty support. See how one user repaired his bad Optibike battery pack himself in our story here.



  • Stealth Bomber  (read review here)
  • $12,000
  • 83V X 20-Ah = 1500 watt hours
  • Claimed range: 50  miles
  • EB “Real Life” range: 50+ miles
  • Weight: 125 pounds
  • Motor: 4500 watt direct drive hub motor
  • Battery cells: LiFePO4 soft pouches
  • Battery life expectancy: 1000  charges
  • Battery warranty (unconditional): 1 year
  • Battery replacement cost $2000 (plus labor charge, battery is built into bike)

The Stealth Bomber is capable of 50-MPH, but even with its gigantic 1500 watt hour battery pack you will drain the pack very quickly with its 4500 watt motor. With the Bomber you pay for all those watt hours not only in high price, but also in weight (125 pounds). These days it’s simply impossible to have all 3…a cheap, lightweight bike, that holds a lot of watt hours.


Eric has been involved in the electric bike industry since 2002 when he started a 6000 square foot brick and mortar Electric Bike store in downtown San Francisco. He is a true believer that small electric vehicles can change the way we operate and the way we think.

  • gdays

    Thank you for taking the time to do this article. currently im trying to build a mid drive bicycle, so this with be very helpfull on choosing the right configuration.

  • ian

    having all 3 is possible, home builds with a 9c and hk lipo will do it.

    • M_111

      What have you found your top mph is with the 9C? We got up to 55mph on a standard old mountainbuike using several 45C LiFe batteries (the true Ah is 1/3 the lead acid equiv since it is for starter battery use, but we had access to a surplus. I believe we started with 24Ah 45C and it was flexing the chassis. The pack lasts longer than the base motive pack on the Zero MX due to the weight and power delivery on the Zero. But only about 10mpH difference in topspeed. We were looking into lower C rate, but higher aH and V for delivery, and as I am sure we all are, trying to save money! I saw an affordable 128Wh pack, but the c rate is only 2.

      • Jeff Kephart

        Do the math, C=Number of times the Ah that a pack can
        discharge w/o damage. So a 20Ah “5c” pack can do 100A
        (for a very brief time)
        If you need 1000watts out of a 24v/24ah you need 50c
        just to avoid damage to the battery.

  • cccccttttt

    Appreciate the article. Watt hours per kilometer is a simple
    international measure of efficiency that works for bikes, trikes, and
    cars, When will the US public shift to metric like the science, military,
    and international community?


    • ElectricBIke

      Yeah the metric system makes so much more sense.

      America is so backwards sometimes.

  • cccccttttt

    To prepare junior high students for ebikes and ecars,

    made up a very brief “Electric Fractions” blurb at

  • Mike

    I would love for someone to give a review of the water bottle type batteries (downtube mount) now coming out of China. I’ve even seen one rated for 36 volts at 12 amps–lithium ion. The nice clean stealth look is attractive. An added bonus is you could just carry an extra battery and swap it out in seconds. Any experience out there? I’m hoping they are not junk.

    • Alex Goldsmith

      It’s useless to swap out the battery. You might as well just connect them in parallel and not make more effort by stopping to swap them

  • juliansmm

    Really good article. I don’t understand what happens when I have a 500W and my battery is 36V x 10aH. I am going to have less speed or less range or both???

    • ElectricBIke

      500 watts is what the motor is rated for and tells you how much wattage it can handle. 36v x 10ah means you have a 360 watt hour capacity battery. If your motor were to burn 500 watts it would go through a 360 watt hour battery in about 40 minutes at wide open throttle….theoretically.

      • Jeff Kephart

        In general V=Speed A=torque.
        Check your CONTROLLER for amp rate that it can handle.
        Volts Times Amps=watts ie 24v into a 35amp PWM is 840w.
        A currie ‘450w’ motor can handle this, the SLA controller can do this too
        (if you feed it the right battery, no way on a factory pack!)
        Amps feel great, but can severely impact range.
        I ran an ammeter in series with the battery and could watch the load
        and feather it out to max the range. 15mph vs 19 was around a 33%
        savings / range increase!

  • Mike Dixon

    Hi great artical. Can you help me please ? Im looking at building a stealth looking bike similar in design to the volton. At minimum i would like to use a 52 volt 2000 watt geared blacklightning motor from HPC with a Li NMC 10 or 12 amp/hr pack in the tube 70mm by 90mm 480mm from the head stem to the crank. can you please tell me if its possible to fit this amount of battery in this space ? If not how could i find out this info ! The idea is to build a bike that can do 60 kph min as discreetly as possible. Basically the more batteries i can fit in the frame bigger the motor i can use so how to find this info love to know.

    cheers Mike

  • B-Rad

    Hi Good article, but I am running into confusion when I am on endless sphere trying to understand the battery jargon used.
    A lot of riders use 4s2p to describe the voltage and capacity of their battery pack.
    I understand that this must mean 4 cells or batteries in series and then those 4 cells or batteries connected in parallel.
    So if I had 3 volt cells at 5 amp hours each the above pack would then be 12 Volts rated at 10 amp-hours.
    Series connections raise the voltage and parallel connections raise the amperage.
    My confusion is when they say 4s2p how can i possibly understand what the voltage is they are running?
    Is there a standard for this?

    • ElectricBIke

      Lipo packs charge to a safe maxium of 4.2 volts per cell….so to be real save and easy lets say 4 volts. A 4s is 4 cells….so figure around 16 volts. If you wire three of these together in series you have a 48 volt pack (what most endless sphere guys would do). If you wire together in parallel you would have tripple the capacity (in amp hours) and the same voltage.

      Hope that helps.

    • Jeff Kephart

      The jargon comes from the RC car industry. S is series (add voltages up)
      P is parallel (add the current/ah capacity)
      My 36ah pack was 96cells (286650 cells) 12P8S to get 24v (29.6 charged)
      It’s a $500 from china battery, but was a BEAST (45mi range with my fat ass
      doing nothing, in hills of Pittsburgh.) 70mi in Florida!

  • jsnyder

    What do you suppose they mean by saying 9ah but with rating of 15ah – that’s confusing. Should I think the range is based on the 9 or the 15? Any idea?


    • micro

      It’s 15 amps, not 15 amp-hours. It’s a detail that’s safe to ignore. The capacity is 9Ah.

      • Jeff Kephart

        I disagree the AMP draw can have dramatic effect on battery life, esp
        with SLA. Hitting a 10ah vs a pair (20ah total) with 800w load I went
        from 5.8 to 19miles. Same trips etc. Same for keeping out of the throttle,
        2/3 throttle drops 4mph and around 1/3 the amp draw.

  • Sunil Kumar

    whats gear diameter in dc motor

  • john

    Maybe put a hub motor and battery on a pit bike. Or put it on something like a Taco 22 or Road Rocket frame. That’d be sick.

  • mtseok

    Ebike does not use total wattage like 360w (36v x 10ah) out of battery capacity. Controller or BMS cuts off the power supply when the battery voltage drops to 30v or something. Do you consider this in your calculating mile per watt? We just use the difference of full charge capacity and the safe cut-off setting, isn’t it?
    – confused from Korea –

    • Jeff Kephart

      Indeed and the overall size of the capacity divided by the PWM current can
      have a large effect on range. On same bike I went from one 10ah@24 SLA pack
      to twin (bike then weighed 94lbs!) And went from 5.8mi to 19mi range.
      Closer to 3x than the 2x that you would expect!

  • Gemini by NexxtDrive

    Appreciate the attempt at getting “real world” range estimates from the advertised ranges. However i would like to understand how the “20 watt hours per mile” standard is arrived at. What sort of drive cycle does this imply? On the flat? If not what is the assumption?

  • ab

    How to decide battery for e-bike with 3.5KW motor running at 48 V

    • Jeff Kephart

      As big as you can afford!

  • zeek

    3 years later no one has done any better for giving real world wh/m estimates.

    estimates without average speed figures are useless. on top fo that, what kind of riding?
    stop and go? hills?

    i very much applaud the necessity to start tracking this stat wh/m in detail and making meaningful figures out of it. these estimates are gold. and yet they are a million miles away from being useful as they don’t give meaningful speeds/ride inclination/stop and go acceleration patterns, rider weight, wind, etc….

    • Jeff Kephart

      My quotes are WOT (wide open) and I explain the terrain.
      Run one of these things non stop around a velodrome and you’d get
      a whole other (pie in the sky) set of numbers.
      I also have found that 3/4 or so throttle can reduce draw 33%
      so 19mph vs 15 is 15 vs 9 amps.
      Having an ammeter you can see and adjusting your habits accordingly, HELPS!

  • Jeff Kephart

    Might also mention that any SLA pack and most lipo etc the “ah” rate is across 20hr
    discharge. The “10ah” currie packs at the 35AMP discharge rate are more like 4-6ah!
    (I got 6mi in Pittsburgh hills on one battery but 19 when I doubled the pack in parallel)
    So, discharge RATE (amperage / wattage of the controller) affects SLA in a very bad
    way and LiFeP04 or LMN less so. A 36ah 24v LiFeP04 on same ezip went 45mi and
    was not quite dead!

  • Jeff Kephart

    Correction, the motor on the ezip was BRUSHED not brushless. Also the brushes are
    unobtainium. (good thing they are good for 5,000+miles!)

  • Derek Johnstone Macrae

    LiNiCoMnO2, i have a 48 volt pack, giving 960 watt hours, the motor is a 1000 watt hub, im getting around 35 miles at 25mph, on level tracks such as canal paths at 15mph, i get close to 50 miles, the pack weighs a measly 6 kilos and cost just £240, if you self build, even cheaper, the chemistry has been out for 2 years and has been further enhanced by NMC cells, which are even more robust although more expensive, expect them to last at least 1000 charges at 100% and around 3000-5000 charges at 70%, that around 6 years of daily use, ali express and ebay now stock mnc and LiNiCoMnO2 batteries, and you can easily pick up 20 amp hour packs for around £250 direct, or £350 uk stock, thats around HALF the price of lipo4 20 amp hour packs

  • Annemieke

    Does the explanation about how to calculate the range performance of an e-bike also apply to an e-bike with pedal assistance? Or is it only applicable for e-bikes of which only the motor is used?

    • Jeff Kephart

      The only way that makes sense is to speak of motor only.
      Since, if you pedal, range could be unlimited!
      My tests are real street riding, and I explain terrain. Since rare is the use
      that is ONLY flat and NO wind etc.

      • Annemieke

        What I mean is if the calculation is for the use of a motor only without peddaling at the same time? Or is the calculation for the motor usage together with peddaling, so that the motor is meant as assistence to a speed of e.g.18- 23 km/h?

  • Jon

    How many miles at full throttle will a 500 watt 36 volt e bike go that has 3-12 volt 18 AH lead acid batteries ?

    • Jeff Kephart

      How long does it take for your grandmother to knit a scarf?
      There are MANY FACTORS beyond 36v at 18Ah and 500watts.
      What tires? Tire pressure? Surface you are on, how fat are you?
      What does bike weigh?
      Let me start with the controller (assuming brushed motor) how many amps
      max is the controller? How much does it draw on the flat?
      the “18ah” capacity is ONLY ACROSS 20 HOUR DISCHARGE TIME.
      Faster discharge=less Ah. So if you draw .9A for 20hrs that is 18Ah.
      if your bike only drew 9/10hs of 1 amp, you could ride for 20hrs.
      if your controller wide open, up a hill draws 30amps (1080w) your “18Ah”
      Will be more like 10Ah and you might get 20miles out of it.

      Putting this in car terms.
      Ah=side of petrol tank.
      Volts=max speed
      Tire pressure, width of tires, wind drag, vehicle weight. ALL are factors!

      This is what the thread is about, you can only measure and get your own
      results, mostly you can IGNORE the manufacturers statements of expected
      range, or assume you will get HALF.
      On my bike, with 1.9″ tires 26″ wheels, 96kg rider, 38kg weight and 20ah
      of SLA into a 450w motor, in HILLY area I got 19miles. (65 psi tires)
      Same bike, same tires, same etc, but FLORIDA where it is almost totally

      flat would do 40+ miles per charge.
      Watching the battery lights or an ammeter I found I could drop from wide
      open (19.8mph) to 15Mph and go from 9.8A to 6A, 19miles became 30.
      For just a bit less speed!
      Pedal and get this even wide open, or do even better.

      So sorry there is no “what will x and y get me?” simple answer or formula.
      My SLA bike used about 1Ah per mile on 24v system. In hilly city.
      My OTHER bike (250w hub motor, 28mm tires, 85psi, alloy frame)
      And LiMn 10ah batt got same range as the 20ah SLA bike, but req
      300% more peddle to make the hills (also was 1/3 the effort to pedal)
      I have hip and knee issues and is the reason I have an ebike. Some

      days I can pedal some, some days a lot, some days NONE. And this
      can change 10miles from home. The ebike gets me home!

      • Chaim Halberstam

        what a great answer, I wish I’dv read it before I attempted my own answer and comparison

  • Peter Marcus

    This article assumed that the batteries even make their claimed capacity. My 960 watt-hour battery is really only 823 watt-hours. I have tested the range in the real world and I get 42 miles and that is with hills. If I pedal all the time and lower the motor assist, I can get as low as 7.5 watt-hours per mile and have a 109 mile range.

  • Steven Cook

    meh, I’d rather buy a car for the same price as these bikes. bring the cost down to below $1000US and then we’ll talk.

    • Jeff Kephart

      would have to be a very cheap car.
      I have $1,000 in a bike that can do 70+mi on the flat with ZERO PEDAL.
      Recharges at $0.002266/mile (based on 10c/KWh)

      • Steven Cook

        I can buy three mopeds on Ebay for the same price as one of these E-bikes.

        • Jeff Kephart

          done the cost of running a moped?
          bet it’s a bit more than a quarter penny per mile.

  • Tom Miguel

    How much watt hours will a 5000 watt motor use at say 50 miles per hour? is there a calculation for speed/WH usage? or do we still use the 20watts per mile

    • Jeff Kephart

      WTF is “20 watts per mile”???
      A 50mph bike / 5KW motor is going to use a MASSIVE
      amount of energy. Wind resistance alone will make the
      needed energy square several times.
      Look at the prices of the factory electric MOTORCYCLES.
      (and their range)
      Or a TESLA car.
      I guess you are confusing watts with watt/hours?
      Or Kwh (thousands of watt hours?)
      50mph and 20Kwh per mile? Possibly.
      Betting you could spend $20,000usd in batteries to make this
      thing run 10miles @ 50mph.

      • Chaim Halberstam

        Well not quite $20k but maybe $2k if you want a lil range on your bike… I’m NO EXPERT as I’ve only recently go into E-bikes but as an example, my current build features a (mere 😉 1500w nominal leafmotor with a 16*4 winding, mated to an 18fet 4110 lyen edition Infineon controller and fed by a 72v 24s1p 30ah lifepo4 prismatic (soft pouch) A123 3c-8c high discharge cells, battery pack with a 60-120a BMS. Although I currently have it limited to 30mph (much longer range and no heat issues) I could quite easily re-program the controller for the stated 50mph and I’m confident my battery would definitely triple that 10 mile estimate, despite wind resistance at higher speeds. I should mention that my pack cost LESS than $1k delivered (but weighs 17kilo) so centering and balancing that weight accurately (and low as poss) on your frame is a priority (And although my bike might look like one, it’ll never be jumped like a stealth, which has amazing engineering IMO.) So if 50 mph (not higher) is the goal, for a city commuter one doesn’t need a 5000w battery power sucking, monster Cromotor (or bigger!) run @72v or higher to acheive that. No, imo, a more modest 1500w unit (Leaf’s best is about 90% efficient @48v) mated to a quality, min 12 fet (reprogrammable) controller is the way to go.