Watt to kWh Calculator
Convert watts to kilowatt-hours — per day, per month and per year — with the cost at your tariff.
Watts are power; kilowatt-hours are energy — and the bill is in kilowatt-hours. This calculator is the step between them, for one device, per day, month and year.
Enter the watts and the hours; the kWh and the cost follow.
Your results
Enter your measurements and press Calculate.
Quantities are rounded up to whole tiles, planks, boxes or bags, after the wastage allowance. Cost appears only when you enter a price.
Formula
All lengths are converted to a single unit before the calculation: 1 ft = 0.3048 m, 1 in = 25.4 mm, 1 ft² = 0.09290304 m², 1 yd² = 9 ft². Material quantities are rounded up — you cannot buy part of a tile, plank or bag.
How to use this calculator
- Enter the watts.
- Enter the hours per day.
- Enter your tariff.
- Read the kWh per day, month and year, and the cost of each.
Worked example
| Device | 100 W, 5 hours a day |
|---|---|
| Per day | 100 × 5 ÷ 1,000 = 0.5 kWh |
| Per month | 0.5 × 30 = 15 kWh |
| Per year | 0.5 × 365 = 182.5 kWh |
| Cost per day at $0.15/kWh | 0.5 × $0.15 = $0.08 (rounded) |
Check it by hand: every step above uses the formula in the box. If your numbers match the example inputs but the calculator gives a different answer, please report it via the contact page.
Frequently asked questions
What is a kilowatt-hour?
1,000 watts running for one hour. A 100 W device for 10 hours uses 1 kWh. Electricity is billed in kWh — this calculator is the conversion.
How many watts are in a kilowatt?
1,000 W. So 100 W is 0.1 kW, and 0.1 kW for 5 hours is 0.5 kWh.
Why is the daily cost rounded?
Because 0.5 kWh × $0.15 is $0.075, shown as $0.08. The monthly and yearly costs use the unrounded kWh, so they stay exact.
Is this a quote?
No. It is a conversion from your own watts, hours and tariff — not a guaranteed bill.
Related calculators
Estimates only. Results are for planning. Measure twice, confirm box coverage and tile sizes on the packaging you buy, and follow the manufacturer's instructions. See the disclaimer.