Watt Hours Calculator
Watt-hours measure total energy consumed over time. A 100-watt light bulb running for 8 hours uses 800 watt-hours (0.8 kWh). At $0.12 per kWh, that costs about 10 cents. This calculator converts watts and time into watt-hours, kilowatt-hours, and gives you the cost at your electricity rate.
The formula:
Energy (Wh) = Power (W) × Time (hours)
Divide by 1,000 to get kilowatt-hours (kWh), which is the unit on your electric bill.
Common appliance costs (at $0.12/kWh):
- LED bulb (10W) for 8 hours: 0.08 kWh = $0.01/day
- Laptop (50W) for 8 hours: 0.4 kWh = $0.05/day
- TV (100W) for 5 hours: 0.5 kWh = $0.06/day
- Space heater (1,500W) for 8 hours: 12 kWh = $1.44/day ($43/month)
- Window AC (1,200W) for 10 hours: 12 kWh = $1.44/day
- Electric oven (2,500W) for 1 hour: 2.5 kWh = $0.30
Battery capacity:
Watt-hours also measure battery storage. A laptop battery rated at 60 Wh can power a 15W load for 4 hours. Portable power stations are rated in Wh (300Wh, 500Wh, 1000Wh). An electric car battery is measured in kWh, typically 40-100 kWh.
Converting units:
- 1 kWh = 1,000 Wh
- 1 Wh = 3,600 Joules
- 1 kWh = 3,412 BTU