What this calculator does
E-bike range is usable battery energy divided by energy use per kilometre. A 500 Wh battery with a 10% reserve leaves 450 Wh usable, and at 15 Wh per kilometre that is 30 km.
Energy use per kilometre is the variable that matters and the one riders have least sense of. It ranges from about 5 Wh/km for gentle assistance on the flat to 25 or more with high assistance, hills, a heavy load or a headwind. That five-fold spread means the same battery can deliver anywhere from 90 km to 18 km.
The formula
The usable energy is the battery capacity less the reserve percentage. Range is that usable energy divided by the energy use per kilometre. The full-battery figure ignores the reserve, and the range per 100 Wh normalises the result so batteries of different sizes can be compared on efficiency alone.
| Term | Meaning |
|---|---|
| Wh/km | Energy consumed per kilometre, the dominant variable in range. |
| Reserve | Capacity deliberately left unused, both as a safety margin and because deep discharge shortens battery life. |
| Usable capacity | Nominal capacity less the reserve, which is what the range is actually calculated from. |
The inputs explained
| Field | What to enter |
|---|---|
| Battery capacity (Wh) | Battery capacity in watt-hours. Multiply volts by amp-hours if the battery is rated that way: 36 V and 14 Ah is 504 Wh. |
| Energy use (Wh/km) | Energy use in watt-hours per kilometre. Around 5 to 8 for low assistance on the flat, 10 to 15 typical, 20 or more for high assistance and hills. |
| Reserve charge to keep (%) | Percentage of capacity held back. 10% is a reasonable margin. |
When to use it
Planning whether a ride is within range
The everyday question, and the one where the consequence of getting it wrong is pedalling a heavy bike home unassisted.
Comparing two batteries
The range per 100 Wh figure strips out battery size so two bikes can be compared on how efficiently they use energy.
Understanding why manufacturer figures are optimistic
Quoted ranges generally assume the lowest assistance level, flat ground and a light rider. Entering realistic Wh/km shows how far the real figure sits below it.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How far does a 500 Wh battery go?
A fixed battery across a range of energy consumption figures.
| Energy use | Estimated range | Usable energy | Range per 100 Wh |
|---|---|---|---|
| 10 Wh/km | 45.0 km | 450 Wh | 10.0 km |
| 15 Wh/km | 30.0 km | 450 Wh | 6.7 km |
| 20 Wh/km | 22.5 km | 450 Wh | 5.0 km |
| 25 Wh/km | 18.0 km | 450 Wh | 4.0 km |
Questions
How many watt-hours does my battery have?
Multiply the voltage by the amp-hour rating. A 36 V 14 Ah battery is 504 Wh, and a 48 V 14 Ah battery is 672 Wh. Comparing amp-hours across batteries of different voltages is meaningless, which is why watt-hours is the useful figure.
Why is my real range less than advertised?
Because quoted ranges typically assume the lowest assistance setting, flat ground, a light rider, mild weather and no stops. Real riding involves hills, wind, traffic lights and higher assistance, all of which raise Wh/km considerably.
What uses the most energy?
Climbing, by a wide margin, followed by headwind and high assistance settings. Rider and cargo weight matter mainly on climbs. Cold weather reduces usable battery capacity as well, sometimes by 20% or more below freezing.
Should I run the battery flat?
Better not to routinely. Lithium batteries last longer when kept between roughly 20% and 80% charge, and deep discharges accelerate ageing. The reserve in this calculation serves both as a range safety margin and as battery care.
For gearing on the same bike, see the bike gear calculator. For how efficiently a rider turns power into speed, see the power to weight calculator.