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Electricity • Consumption • kWh

Calculate kWh

Calculate energy consumption in kilowatt-hours from power and runtime.

Calculation Values

Note: This calculator provides a technical estimate for guidance only. For electrical installations, standards, protective measures, installation method, ambient temperature, grouping, protective devices and manufacturer specifications must also be checked.

Formula Used

kWh = (Watts ÷ 1000) × Hours × Days

Consumption in kWh results from power and usage time.

Frequently Asked Questions

What is a kilowatt-hour?

A kilowatt-hour is the energy consumed by a device with 1 kW of power over one hour.

Is a watt the same as a kWh?

No. A watt is power, a kWh is energy consumption over time.

How do I calculate annual consumption?

Use 365 as the number of days and enter the average daily runtime.

Practical guidance

Calculate energy use from power and time

Kilowatt-hours measure energy, not instantaneous power. The calculator sums a constant load over hours and days.

Input values explained

Power in watts
Use the electrical active power drawn by the load. A nameplate, data sheet or power meter is more reliable than an estimate.
Operating time
Enter the actual operating time in the period considered. Thermostatically controlled or cycling devices rarely run continuously at rated power.
Number of days
This value extrapolates an identical daily usage pattern. Seasonal and weekday differences are not included automatically.

Example: a 1 kW device for one month

A 1,000 W appliance runs five hours on each of 30 days.

(1,000 W ÷ 1,000) × 5 h × 30 = 150 kWh

Consumption is 150 kWh. At 500 W and the same operating time it would be 75 kWh.

Allow for changing power

For devices that cycle between full, partial and standby modes, use average measured power or a measured kWh total.

Calculation limits

  • Short inrush peaks usually add little energy but may affect electrical design.
  • The result contains no cost or emissions factor.