Free EV tool
EV Motor Power & Torque Calculator
Size a traction motor from first principles: vehicle mass, rolling resistance, aerodynamic drag, the hill it must climb and how fast it must accelerate. Works for e-bikes, scooters, 3-wheelers and cars.
Continuous power
4 kW
top speed or gradient, whichever is higher
Peak power
7.7 kW
for seconds — usually acceleration
At top speed
4 kW
On gradient
1.8 kW
Acceleration
7.7 kW
Wheel torque
97 Nm
start on gradient +20 %
Motor torque
114 Nm
Motor speed
807 rpm
at top speed
Forces: rolling 32 N · air drag at top speed 143 N · gradient 320 N
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Motor sizing report
Motor Power & Torque Calculator ·
Inputs
| Mass | 220 kg |
| Crr / Cd / area | 0.015 / 0.9 / 0.7 m² |
| Targets | 70 km/h top, 15 % at 15 km/h, 0–40 km/h in 5 s |
| Wheel / gear / efficiency | 0.23 m / 1:1 / 85 % |
Results
| Continuous / peak power | 4 kW / 7.7 kW |
| Top speed / gradient / acceleration | 4 / 1.8 / 7.7 kW |
| Wheel / motor torque | 97 / 114 Nm |
| Motor speed at top speed | 807 rpm |
- Check the motor's continuous rating at your worst ambient temperature, and that the controller's phase current covers the peak torque.
Estimates for planning — verify against datasheets and supplier quotes before you build or invest. Recalculate or share:
Learn to design this hands-on: emobility.academy/courses
How it's calculated
Road load F = m·g·Crr·cos θ (rolling) + ½·ρ·Cd·A·v² (air drag, ρ = 1.2 kg/m³) + m·g·sin θ (gradient, θ = atan(grade % ÷ 100)).
Power P = F × v ÷ drivetrain efficiency. The calculator works it out three ways: cruising at top speed on the flat, climbing your gradient at its speed, and the end of the acceleration run (F = 1.05·m·a + road load, the 5 % covering rotating inertia).
Continuous rating is the larger of top-speed and gradient power — the motor must hold those indefinitely. Peak rating is the largest of all three — usually acceleration, held for seconds.
Wheel torque to start on the gradient = road load at standstill × wheel radius × 1.2 (20 % margin). Motor torque divides that by the gear ratio and efficiency; motor RPM at top speed = wheel RPM × gear ratio. Hub motors have a ratio of 1.
Results are engineering estimates for planning and learning. Check them against datasheets, supplier quotes and the applicable standards before you build or invest.
Frequently asked questions
How many kW motor does an electric scooter need?
A 150–200 kg loaded scooter needs about 2–3 kW continuous to cruise at 60–70 km/h and 4–7 kW peak for brisk acceleration and flyovers. Run your own numbers above.
What is a typical rolling resistance coefficient?
About 0.010–0.015 for car tyres on asphalt, 0.012–0.02 for scooter tyres, and 0.02–0.03 for 3-wheeler tyres on poorer roads.
Continuous vs peak motor power — which goes on the spec sheet?
Both. Type-approval documents state rated (continuous) power, while brochures often quote peak. A 2.5 kW hub motor may have a 5 kW peak for 30–60 seconds.
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