Electricity Cost Calculator
Enter device watts and hours per day (or metered kWh) plus your electricity rate ($/kWh) to calculate daily, monthly, and yearly appliance running costs.
Open calculatorLast updated: 2026-10-13
How the calculation works
- Two entry methods: device watts × hours (with a multiplier for identical devices), or a known daily kWh figure from a meter or smart plug.
- Energy = watts × hours ÷ 1000 gives kilowatt-hours; the tool extrapolates to month (30.44 days) and year (365 days).
- Cost multiplies energy by your rate — use the all-in rate including delivery charges for real accuracy.
Worked example
Interpreting the result
The yearly figure is the one to compare against alternatives: a $400 heat-pump replacement of that heater saving 60% pays back in about 2 years. Devices that run 24/7 (fridges, servers, aquariums) dominate household consumption even at modest wattage.
Assumptions
- Constant wattage while running — devices with compressors cycle and use less.
- Flat electricity rate; tiered or time-of-use pricing needs an average.
Limitations
- Standby consumption (0.5–5 W when 'off') is not counted — add it for always-on electronics.
- Does not model demand charges or fixed connection fees.
Typical wattage and estimated running costs for household appliances
- Space Heater (1,500 W): 4 h/day at $0.15/kWh = 6.0 kWh/day → ~$27.40/month ($328/year).
- Central Air Conditioner (3,500 W): 6 h/day = 21.0 kWh/day → ~$95.90/month in peak summer.
- Electric Water Heater (4,500 W, cycles ~3 h/day): 13.5 kWh/day → ~$61.60/month ($740/year).
- Refrigerator / Freezer (150 W avg duty): ~1.5 kWh/day → ~$6.85/month ($82/year).
- Desktop Gaming PC (450 W): 5 h/day = 2.25 kWh/day → ~$10.30/month ($123/year).
- Level 2 EV Charger (7,200 W / 32 A): 4 h full charge = 28.8 kWh → ~$4.32 per charging session.
Frequently asked questions
How do I calculate appliance running costs?
Find the wattage on the appliance label, multiply by the hours used per day, divide by 1,000 to get daily kWh, and multiply by your utility's electricity rate per kWh ($/kWh). Formula: Cost = (Watts × Hours / 1,000) × Rate.
How do I find my electricity rate and kWh price?
Look at your most recent electric bill and divide the total final balance by the total kWh consumed. This gives your effective all-in price per kWh including transmission, delivery, and taxes.
How do I calculate cost from kWh directly?
Switch the input method to 'Known energy' and enter the kWh (from a meter or smart plug reading): cost = kWh × your rate. No wattage estimate needed.
How much does leaving a light on cost?
A 60 W incandescent on 24/7 at $0.15/kWh costs $79/year. An equivalent 9 W LED costs $12/year — the classic efficiency argument.