Before you can size a solar system, a generator or a battery, you need to know how much energy your appliances use each day. That number is measured in watt-hours (Wh) or kilowatt-hours (kWh). This guide shows how to work it out for any appliance in a few minutes.
Watts vs watt-hours
Watts (W) measure how fast an appliance uses power at a moment in time. Watt-hours (Wh) measure how much energy it uses over time. A 100 W bulb running for 1 hour uses 100 Wh. Running for 5 hours uses 500 Wh. And 1 kWh equals 1,000 Wh.
The formula
- Watts: the appliance's power draw.
- Hours per day: how long it is switched on.
- Quantity: how many identical units you have.
- Cycle: the share of the time it actually draws full power, written as a decimal. Use 1 for items that run steadily, like lights. A fridge compressor is about 0.3 to 0.4 because it switches on and off.
Where to find the watts
- The label or manual: look for "W" or "watts" on the sticker or in the specs.
- Amps and volts only? Multiply them: Watts = Volts x Amps. A 120 V appliance rated 5 A is about 600 W. For a 230 V appliance rated 2 A, it is about 460 W.
- A plug-in power meter: the most accurate method. It shows real watts and total kWh over days. These meters are inexpensive.
Labels often show the maximum power, so real use is frequently lower.
Example: a small home
| Appliance | Watts | Hours/day | Cycle | Wh/day |
|---|---|---|---|---|
| LED light | 10 | 5 | 1 | 50 |
| TV | 100 | 4 | 1 | 400 |
| Laptop | 60 | 6 | 1 | 360 |
| Refrigerator | 150 | 24 | 0.35 | 1,260 |
| Ceiling fan | 70 | 8 | 1 | 560 |
| Microwave | 1,200 | 0.3 (18 min) | 1 | 360 |
| Total | 2,990 Wh = about 3 kWh | |||
That is about 3 kWh per day, or roughly 90 kWh per month.
Try the daily energy calculator
Add your own appliances below, or pick from common ones. The calculator works out the Wh for each row, your daily total in Wh and kWh, and your monthly kWh. You can export the result as a PDF.
Daily Energy Calculator
Add your appliances and get Wh and kWh per day
Cycle = share of time the appliance draws full power (1 for steady loads, about 0.35 for a fridge). Estimates only. Have your final design reviewed by a qualified electrician or installer.
Using your electricity bill
If you only want a rough total, your bill shows kWh used per month. Divide by 30 for a daily figure. For example, 450 kWh per month is 15 kWh per day. A bill is a good way to check that your appliance list adds up.
Common mistakes
- Forgetting standby power: chargers, routers, TVs and set-top boxes draw small amounts all day. Add them up.
- Treating a fridge as always on at full power. Use a cycle value or measure it.
- Ignoring start-up surge: motors like pumps and compressors can draw 2 to 3 times their running watts for a moment. That does not change daily Wh much, but it matters for sizing an inverter.
- Using summer numbers only. Heating, cooling and lighting change by season.
Next step
Once you have your daily kWh, you can work out how many solar panels you need and how big your battery bank should be. Read our guides: How Many Solar Panels Do I Need? and How to Size a Solar Battery Bank.
Disclaimer: This article is for general information and education only. Numbers are estimates and examples, not professional advice or a certified design. Have your final design reviewed by a qualified electrician or installer and follow your local codes and utility rules.
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