E-Bike Range With Reserve Calculator
Estimate how far your e-bike can travel before reaching a chosen battery reserve using battery capacity, starting charge, and Wh/km or Wh/mi.
Last updated: July 2026
Estimated range before reserve
E-bike range with reserve formula
Starting energy = Battery Wh × Starting charge %
Reserve energy = Battery Wh × Reserve %
Usable energy = max(0, Starting energy − Reserve energy)
Range = Usable energy ÷ Energy use per kilometer or mile
Percentage values are converted to decimals; for example, 20% = 0.20.
This is a planning estimate based on your entered energy use, not a guaranteed or safe maximum distance. Actual consumption and reserve indication can vary.
How this e-bike range calculator works
This calculator divides battery energy available above your selected reserve by your entered energy use per kilometer or mile. It provides an estimated planning range rather than inventing opaque terrain, weight, temperature, or assist-level adjustments.
E-bike range with reserve formula
Starting energy equals battery Wh multiplied by starting charge as a decimal. Reserved energy equals battery Wh multiplied by reserve percentage as a decimal. Usable energy is the greater of zero or starting energy minus reserved energy. Range equals usable energy divided by Wh/km or Wh/mi.
A 20% reserve means 20% of the full entered battery capacity even when starting charge is below 100%. It is not 20% of the current charge.
What does Wh/km mean?
Wh/km means watt-hours of battery energy used to travel one kilometer. If a bike averages 12 Wh/km, each kilometer uses approximately 12 Wh; 600 usable Wh divided by 12 Wh/km gives 50 km. Wh/mi expresses the same idea per mile. Lower consumption produces more calculated range, while higher consumption produces less.
Calculating battery Wh from voltage and amp-hours
Nominal watt-hours equal volts multiplied by amp-hours. For example, 48 V × 20 Ah = 960 Wh. This is the nominal energy implied by entered label ratings. Real usable energy can differ because of battery condition, BMS limits, temperature, voltage behavior, and other factors; no automatic degradation factor is applied.
Why your actual e-bike range can change
Hills and elevation, rider and cargo weight, speed, assist level or throttle use, repeated acceleration and stopping, headwinds, tire pressure, temperature, and battery age or condition can all change actual energy consumption. In this model those conditions appear as changes in measured Wh/km or Wh/mi rather than arbitrary hidden penalties.
Worked examples
48 V, 21 Ah battery
48 × 21 gives 1,008 Wh. Starting at 100% with a 20% reserve leaves 1,008 − 201.6 = 806.4 Wh above reserve. At 12 Wh/km, estimated range is 67.2 km, approximately 41.76 mi.
Partially charged 672 Wh battery
At 75% charge, starting energy is 504 Wh. A 15% full-capacity reserve is 100.8 Wh, leaving 403.2 Wh. At 14 Wh/km, estimated range before reserve is 28.8 km.
Energy use entered in Wh/mi
A 1,000 Wh battery starting at 80% with a 20% reserve has 600 Wh above reserve. At 20 Wh/mi, estimated range is 30 mi, approximately 48.28 km.
Starting below reserve
A 500 Wh battery at 20% contains 100 Wh, while a 30% reserve represents 150 Wh. Usable energy above reserve is max(0, 100 − 150) = 0 Wh, so estimated distance before reserve is 0 km.
Frequently asked questions
How do you calculate e-bike range from battery Wh?
Divide usable battery watt-hours above the selected reserve by energy use in Wh per kilometer or mile.
How does a battery reserve affect range?
Energy represented by the reserve is excluded from the planned ride, reducing the distance calculated before that threshold.
Is e-bike range based only on battery size?
No. Battery energy is one part of the calculation. Actual energy use changes with route, riding style, payload, weather, bike setup, and battery condition.
What if I start with less than 100% charge?
The calculator uses your entered starting percentage and does not assume a fully charged battery.
What if my selected reserve is higher than my current charge?
Estimated range before reserve is zero because the battery is already at or below that planning threshold. The input remains valid.
How do I calculate Wh from volts and amp-hours?
Multiply nominal voltage by amp-hours: Wh = V × Ah.