Physics-first range prediction for electric bikes

Most e-bike range tools divide battery capacity by average watt-hours per kilometre and call it done. That works on flat ground with no wind at constant speed — conditions that almost never apply in the real world.

Our calculator models the actual physics of cycling:

• Aerodynamic drag — drag force scales with the square of velocity, so riding at 25 km/h takes roughly twice the energy of 18 km/h. We calculate drag from your CdA (drag coefficient × frontal area), which varies by riding position and bike type.
• Elevation and gradient — climbing 100 metres of elevation requires approximately 9.8 kJ of mechanical energy per kilogram of total system weight. We integrate this over your full GPX route.
• Rolling resistance — terrain surface, tire type, and pressure all affect how much energy the tyres absorb. A gravel tire at 40 PSI on dirt costs 2–3× more rolling energy than a road tire at 90 PSI on tarmac.
• Wind — a 20 km/h headwind is not symmetric with a 20 km/h tailwind. We model the actual vector addition of wind and rider velocity.
• Motor and drivetrain efficiency — motor efficiency varies with load and speed. We apply efficiency curves to convert mechanical power requirements to electrical power drawn from the battery.
• Temperature — lithium batteries deliver less capacity in cold weather. Below 5°C, usable capacity typically drops 15–25%. Below 0°C, losses can reach 30–40%.
• Pedalling contribution — the assist ratio you ride at changes how much the motor contributes vs. your legs. Eco mode may draw 150–200 Wh/km; turbo mode on the same route could draw 400+ Wh/km.

When you upload a GPX file, we analyse every metre of the route profile to compute a terrain-accurate prediction. Without GPX, you can enter average elevation gain manually for a good approximation.

Under good input conditions (accurate weight, correct battery capacity, real elevation data), our estimates are typically within 10–15% of actual range.

The largest sources of real-world deviation are:

• Battery age — a 3-year-old battery may have 80–85% of its rated capacity. Enter your estimated current capacity, not the label value, for older bikes.
• Riding style variability — frequent hard acceleration (traffic stops, trail obstacles) can increase consumption by 20–30% vs. steady-state cruising.
• Motor calibration — assist sensitivity, motor cut-in speed, and throttle maps vary significantly between manufacturers and firmware versions.

The brand and model pages on this site compile published manufacturer specifications (battery capacity in Wh, motor power in W, weight, category) and run them through our range model to produce eco / normal / sport range estimates.

Manufacturer range claims are typically measured under optimal lab conditions (level road, slow speed, light rider, warm temperature). Our estimates reflect more realistic mixed-use riding conditions and are intentionally more conservative.

Supported brands include Bosch, Giant, and others available at ebike.futornyi.com/range/brand/.

Questions about the calculator, model data, or methodology? Use the contact page to get in touch.