Calculating your energy used is straightforward once you know the Watt-Hours (kWh) formula and what each input means. This guide explains the method in plain language, walks through a manual calculation, and gives worked examples you can follow — then you can do it instantly with the Watt-Hours (kWh) Calculator.
What is Watt-Hours (kWh)?
The Watt-Hours (kWh) calculation tells you your energy used from a few simple inputs. The figure you are solving for here is the energy used.
The Watt-Hours (kWh) formula
The core formula is:
Energy used = Power × Time used ÷ 1000Here is what each input means:
- Power — a value measured in W. Example: 60 W.
- Time used — a value measured in hours. Example: 5 hours.
How to calculate it step by step
- Write down the power (for example, 60 W).
- Write down the time used (for example, 5 hours).
- Apply the formula above to get your energy used.
- Double-check the result with the Watt-Hours (kWh) Calculator.
Worked examples
Example 1
| Input / Output | Value |
|---|---|
| Power | 60 W |
| Time used | 5 hours |
| Energy used | 0.3000 |
| In watt-hours | 300.0 |
With power of 60 W and time used of 5 hours, the energy used works out to 0.3000.
Example 2
With power of 120 W and time used of 5 hours, the energy used works out to 0.6000.
| Result | Value |
|---|---|
| Energy used | 0.6000 |
| In watt-hours | 600.0 |
Example 3
With power of 30 W and time used of 5 hours, the energy used works out to 0.1500.
| Result | Value |
|---|---|
| Energy used | 0.1500 |
| In watt-hours | 150.0 |
Tips for an accurate result
- Keep your units consistent — mixing, say, months with years or grams with kilograms is the most common source of error.
- Round only at the very end. Rounding inputs early can shift the final answer noticeably.
- Re-run the numbers whenever an input changes, rather than estimating from an old result.
Prefer not to do the maths by hand? — the Watt-Hours (kWh) Calculator does it instantly, for free, with the formula and a worked example built in.
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