EleCanada
Energy and power

Energy duration calculator

Convert any two of constant-power energy, power and operating time into the third quantity.

Calculation inputs

Known quantities

kWh
kW

Use real energy and power at the same measurement boundary. This model assumes constant power for the stated time.

Enable JavaScript to calculate. The formula and scope remain below.

Energy relationship result

Enter the two known quantities.

Constant-power arithmetic only. No efficiency, standby load, cost, demand factor or equipment capacity is applied.

What it calculates

Enter any two of energy, real power and operating time at the same measurement boundary. The calculator returns the third quantity and repeats the supplied values in a consistent unit set: kWh, kW and hours.

Use energy already defined for the load or system boundary. Do not add a battery reserve, inverter efficiency or standby consumption unless those quantities are part of the supplied energy or power value.

Method and examples

The relationship is energy = power × time. The inverse forms are power = energy ÷ time and time = energy ÷ power.

Eight kWh at a constant 2 kW takes 4 hours in this model. A 2 kW load running for 4 hours uses 8 kWh. These are arithmetic examples, not equipment ratings.

Zero energy with positive power returns zero time. A zero power or zero time input cannot establish the requested ratio and is rejected.

Limits and interpretation

This is a constant-power relationship. It does not model changing load, charging curves, conversion losses, battery reserve, temperature, demand factors, tariffs or equipment operating limits.

For battery runtime, use the battery runtime calculator with available energy at an explicit AC or DC boundary. For EV charging, use the EV charge time calculator, which states its SOC and efficiency assumptions separately.

No conductor, breaker, service, battery, generator or inverter selection is provided.

Common questions

Can I enter kW and hours to estimate energy use?

Yes. Choose “Power and operating time”, then enter the constant real power and duration. The result is kWh.

Does this include efficiency?

No. Enter energy and power at the same boundary. Apply a documented efficiency separately only when the system boundary requires it.

Can I use a breaker rating as power?

No. A breaker rating is not the same as measured real power. Enter a real-power value for the load or system being described.

Battery runtimeEstimate runtime from available energy and load.EV charge timeEstimate a constant-power AC charging window.Connected loadTotal loads sharing a voltage, phase and power factor.

Source

BC Hydro, Battery Energy Storage System (BESS) Best Practices Guide, section 3.1, printed page 6: distinguishes energy capacity from power and describes storage duration as the energy-to-power relationship. The source's storage-specific definitions are not imported into this general arithmetic tool.

Source and scope checked November 10, 2026. Report a problem or suggest a source; inputs are not attached automatically.