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Regenerative Braking Energy Calculator

Enter the vehicle mass, speeds and recovery efficiency to estimate the energy reclaimed during braking.

How it is calculated

Speeds are entered in km/h and converted to m/s by dividing by 3.6. The kinetic energy lost between the start and end of the braking event is then scaled by the recovery efficiency:

ΔKE = ½ × m × (v₁² − v₂²) (m in kg, v in m/s, result in joules)
recovered = ΔKE × efficiency ÷ 100
Wh = recovered ÷ 3600

The tool reports the recovered energy in J and Wh, plus the total kinetic energy shed in J. If the final speed is higher than the initial one, the energy change is floored at zero, so the result is 0 rather than a negative number. Mass must be above zero, speeds cannot be negative and efficiency must be between 0 and 100, otherwise no result is shown. It models only the speed drop, not rolling resistance, air drag, gradients or battery limits.

Worked example

A 1500 kg car slows from 50 km/h to a stop with 60% recovery efficiency. 50 km/h is 13.889 m/s, so the kinetic energy shed is ½ × 1500 × 13.889² ≈ 144,676 J. At 60% efficiency the recovered share is 144,676 × 0.60, which the tool shows as 86,806 J. Dividing by 3600 converts that to 24.113 Wh, a small slice of a battery measured in tens of kWh.

Try this example →

Common mistakes

  • Entering speeds in m/s or mph. Both speed fields expect km/h; typing 14 for 14 m/s gives roughly one thirteenth of the real energy.
  • Treating the efficiency as a fraction. Type 60 for 60%, not 0.6, otherwise the recovered energy is a hundred times too small.
  • Entering the speed range backwards. If the final speed is above the initial one, the tool returns 0 J instead of flagging the error.
  • Using the kerb weight but forgetting passengers and cargo. The mass field is the whole moving mass, and the result scales directly with it.
  • Expecting the result to be the range gain. The figure is energy only: it ignores drag and rolling losses during the slowdown, and it is not the extra distance the car can drive.

About this calculator

Regenerative braking recovers a fraction of a vehicle's kinetic energy (KE = ½mv²) by running the electric motor as a generator during deceleration, converting motion back into stored battery charge instead of dissipating it entirely as brake-pad heat. The energy actually reclaimed depends on the drop in speed — from v₁ down to v₂ — and a recovery efficiency factor that accounts for losses in the motor, inverter and battery charging path, typically 60-70% in real-world EVs and hybrids rather than the full theoretical kinetic energy difference.

This calculator takes a vehicle's mass, its speed before and after braking, and a recovery efficiency percentage, then estimates the energy actually reclaimed in joules and watt-hours, alongside the total kinetic energy shed (mass in kg, speeds in km/h). Automotive and EV powertrain engineers modeling energy budgets, hybrid/EV owners curious how much range city braking recovers, and students studying regenerative systems use it to quantify how braking pattern and vehicle mass translate into real energy savings rather than relying on a manufacturer's headline efficiency number.

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