Ohm Calculator
Instant electrical conversions & energy cost estimates.
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Your electricity cost is an appliance’s power in kilowatts times the hours it runs times your rate per kWh — here is how to work it out and see where the money on your bill actually goes.
How to Calculate Electricity Cost per kWh
Utilities bill in kilowatt-hours (kWh) — the energy a 1,000-watt appliance uses in one hour. To find what a device costs, convert its power to kilowatts, multiply by the hours it runs, then multiply by your rate: Cost = (Watts ÷ 1,000) × Hours × Rate.
- Convert watts to kilowatts — a 1,500-watt heater is 1,500 ÷ 1,000 = 1.5 kW.
- Multiply by hours used — running it 4 hours a day is 1.5 kW × 4 = 6 kWh.
- Multiply by your rate — at $0.16/kWh that is 6 × $0.16 = $0.96 per day (about $28.80 a month).
If your appliance is rated in watts, convert it to kilowatts first with our Watts to Kilowatts calculator.
What Drives Your Monthly Bill
Two things decide an appliance's cost: how much power it draws and how long it runs. High-wattage devices used briefly can cost less than modest ones left on around the clock.
- Heating and cooling dominate. Space heaters, AC units, and electric water heaters are the biggest line items on most bills.
- Always-on loads add up. A fridge, freezer, or router runs 24/7 — even at low wattage, thousands of hours a year become real money.
- Phantom (standby) power is real. TVs, consoles, and chargers left plugged in draw a few watts continuously; together they can be 5–10% of a bill.
- Short bursts are cheap. A 1,500-watt kettle used for two minutes costs well under a cent — power matters, but so do the hours.
Running Cost of Common Wattages
At the US average of roughly $0.16/kWh, here is what different power levels cost per hour and per month (assuming 5 hours of use a day):
| Power | Per Hour | Per Month |
|---|---|---|
| 60 W | $0.01 | $1.44 |
| 500 W | $0.08 | $12.00 |
| 1,000 W | $0.16 | $24.00 |
| 1,500 W | $0.24 | $36.00 |
| 2,000 W | $0.32 | $48.00 |
| 3,000 W | $0.48 | $72.00 |
Frequently Asked Questions
What is Ohm's Law? +
Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points, expressed as V = I × R (Voltage = Current × Resistance). It's the foundation for calculating power, where Watts = Amps × Volts.
How do I convert watts to kilowatts? +
Divide the number of watts by 1,000. For example, 2,500 watts equals 2.5 kilowatts. Kilowatts are typically used to describe larger loads and to measure energy consumption on your utility bill.
How is my electricity bill calculated? +
Utilities charge per kilowatt-hour (kWh). Multiply an appliance's power in kilowatts by the hours it runs to get kWh consumed, then multiply by your electricity rate. The Energy Cost tab above does this automatically for daily, monthly, and yearly estimates.
What is a kilowatt-hour (kWh)? +
A kilowatt-hour is a unit of energy equal to running a 1,000-watt appliance for one hour. It is the standard unit used by energy providers to measure and bill electricity usage.