Divide the battery’s watt-hours (Wh) by 15 and you get a rough range in miles. Cycling UK offers this as a “very rough” rule of thumb, and its own example is a 500 Wh battery giving around 33 miles (about 53 km). Treat that number as a starting point, then replace it with your own measured consumption, which is far more reliable.
What watt-hours actually measure
A watt-hour is an amount of stored energy: the battery’s fuel tank. Your motor and your legs spend that energy as you ride. Range is simply the energy available divided by the energy you use per unit of distance. That is why the same battery can take you very different distances depending on how you ride.
Cycling UK notes that 400 Wh, 500 Wh and 625 Wh are becoming standard sizes, while ETA puts typical e-bike batteries between 250 Wh and 750 Wh, with bigger batteries going further. Check the Wh figure printed on the battery or in the spec sheet. If only volts and amp-hours are listed, multiply them together to get Wh.
Method 1: the divide-by-15 estimate
- Find the battery capacity in Wh.
- Divide by 15 for miles. For kilometers, multiply that answer by 1.61.
- Read the result as a mid-range guess, not a promise.
The 15 is really an assumed consumption of 15 Wh per mile. A rider who uses less than that goes farther, and one who uses more goes shorter. Cycling UK stresses that actual range depends on the power level selected, rider weight, terrain and weather, and “can vary massively.”
Method 2: measure your own Wh per mile
This is the method worth adopting, because it captures your bike, your weight and your routes.
- Charge fully and note the starting battery percentage (or bars) on the display.
- Ride a typical route in your normal assist mode and note the distance from your trip meter.
- Note the percentage at the end.
- Energy used = battery Wh x (percentage used / 100). Consumption = energy used / distance.
- Projected range = battery Wh / your consumption.
Repeat on a few different routes and in different assist modes, and keep the lowest and highest results. That gives you a realistic band rather than one number. Battery gauges are approximations and are not linear, so longer test rides give steadier figures than short ones. Our guide to reading your e-bike display explains what the trip and battery readouts show.
Why the answer moves
| Factor | Effect on range | What the sources say |
|---|---|---|
| Assist level | Lower assist stretches the battery | ETA: the lowest assistance can significantly extend range |
| Speed | Slower saves energy | Cycling UK: 13 mph rather than the 15.5 mph assist cutoff usually saves a good amount |
| Terrain and load | Hills, off-road and heavy loads drain faster | ETA lists heavier loads, hills and off-roading as faster drains |
| Weather | Cold and headwinds shorten range | ETA: cold reduces battery efficiency; headwinds reduce range, tailwinds extend it |
| Tire pressure | Soft tires cost distance | ETA quotes a Wisper Bikes executive saying low pressures give very low mileage |
Tire pressure is the cheapest factor to fix: check it before any ride where range matters, as covered in the pre-ride checklist.
How wide the real-world spread is
Published figures show why a single formula only goes so far:
- Cycling UK reports a lightweight road-bike system getting 50 miles or more from a 180 Wh battery, a battery less than half the size of many standard ones.
- At the other extreme, it says a heavy rider on an e-MTB using high power over very demanding off-road terrain could manage fewer than 20 miles from an average-capacity battery.
- ETA’s range for smaller batteries, rough terrain and high assistance is 20 to 30 miles (32 to 48 km).
The sources also disagree in places. The formula gives about 33 miles for 500 Wh, while ETA says a 500 Wh battery “might give you a range up to 50 miles,” which is a best-case ceiling rather than a typical result. ETA also quotes 30 to 40 miles from an average 370 Wh battery, which is more generous than dividing by 15 would suggest. Use the lower figure when planning a ride with no charging option.
Manufacturer range calculators
Some makers offer online range estimators. Cycling UK mentions Bosch’s Range Assistant as a useful guide for seeing how factors change range, but its author has found it a little too generous. Use such tools to compare scenarios, and trust your logged numbers over the output.
Plan with a margin
- Plan routes at the low end of your measured band, especially in cold weather or with a headwind on the return leg.
- Keep the assist mode you will need on the hills in reserve rather than burning it on flat ground.
- If you regularly run short, compare larger batteries, but weigh the extra mass and cost against simply riding in a lower assist mode. See how to choose your first e-bike and real-world range for more.
- Battery health also affects capacity over time; our battery care guide covers keeping it in good shape.
Sources
Last reviewed: October 2026.