What Is an Electricity Cost Calculator?
This calculator estimates how much it costs to run an electrical device or appliance based on its wattage, how many hours a day you use it, and your electricity rate — plus the current draw in amps using Ohm's Law.
How to Use the Electricity Calculator
- Enter the device's power rating in watts (check the label or spec sheet).
- Enter how many hours per day you typically use it.
- Enter your electricity rate (check a recent utility bill for your exact $/kWh).
- Enter the voltage to see the current draw in amps.
Electricity Cost Formula
Worked Example
Power: 1,500W = 1.5 kW
Daily energy: 1.5 kW × 3 hrs = 4.5 kWh
Daily cost: 4.5 kWh × $0.16 = $0.72
Monthly cost (30 days): $0.72 × 30 = $21.60
Current draw at 120V: 1,500W ÷ 120V = 12.5 amps
Understanding Your Results
Monthly Cost projects your typical usage pattern over 30 days. Current Draw (amps) is useful for checking whether a device will overload a circuit — most household circuits are rated for 15 or 20 amps total.
Tips for Reducing Electricity Costs
- Check your utility bill for your exact rate, including any time-of-use pricing that varies by hour.
- High-wattage appliances (heaters, dryers, AC units) typically dominate electricity costs — small reductions in usage time add up.
- Look for the device's actual wattage rating rather than assuming — it's usually printed on a label or in the manual.
Common Mistakes to Avoid
- Confusing watts with amps — they measure different things and are related by voltage (Watts = Volts × Amps).
- Forgetting that many appliances don't run at full rated wattage continuously (e.g., a refrigerator cycles on and off).
- Using an outdated electricity rate — rates can change seasonally or with new utility pricing plans.
Frequently Asked Questions
Convert watts to kilowatts (divide by 1000), multiply by hours used, then multiply by your electricity rate per kWh.
Watts measure the rate of power consumption at any given moment; kilowatt-hours measure total energy used over time (1 kWh = using 1,000 watts for one hour).
Check the label on the device, its spec sheet, or manual — it's usually listed directly, or can be calculated from volts × amps if only those are given.
It calculates the electrical current (in amps) a device draws, based on its power (watts) and the voltage of the circuit it's plugged into.
Most household circuits in the US are rated for either 15 or 20 amps — check your circuit breaker panel or an electrician before plugging in high-wattage devices.