Watts vs kWh: what's the difference?
Watts (W) measure power — how fast an appliance uses electricity at any instant. Kilowatt-hours (kWh) measure energy — power used over time, which is what your utility bills. The link is kWh = (watts ÷ 1000) × hours. So wattage alone doesn't decide your cost; a high-wattage device used briefly can cost less than a low-wattage device left on for hours.
The analogy
Think of water: watts are like the flow rate from a tap (gallons per minute), and kWh are like the total water in the bucket after a while (gallons). A fast tap (high watts) open for a second fills less than a slow tap left running all day. Your meter measures the bucket — total energy — in kWh.
Same wattage, very different cost
| Appliance | Watts | Hours/day | kWh/month |
|---|---|---|---|
| Hair dryer | 1,800 W | 0.1 (6 min) | ~5.4 |
| Refrigerator | 150 W avg | 24 | ~108 |
| Space heater | 1,500 W | 8 | ~360 |
| LED TV | 100 W | 5 | ~15 |
Frequently asked questions
What is the difference between watts and kilowatt-hours?
Watts (W) measure power — the rate electricity is used right now. Kilowatt-hours (kWh) measure energy — power used over time. kWh = (watts ÷ 1000) × hours. Your bill charges you for kWh, not watts.
Is a higher-wattage appliance always more expensive?
No. Cost depends on watts AND hours. A 1,800 W hair dryer used 5 minutes a day costs far less than a 150 W fridge running 24/7, because the fridge accumulates far more kWh over the month.
How do I convert watts to kWh?
Multiply watts by the hours used, then divide by 1,000. For example, 1,500 W for 4 hours = 1,500 × 4 ÷ 1,000 = 6 kWh.
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Last updated: 2026-06-20