Calculate electricity cost for a single device or an entire household, and convert between energy units.
| Period | Energy (kWh) | Cost ($) |
|---|---|---|
| Per Hour | 1.00 | $0.13 |
| Per Day | 8.00 | $1.04 |
| Per Week | 56.00 | $7.28 |
| Per Month | 243.3333 | $31.63 |
| Per Year | 2,920.00 | $379.60 |
| Energy (kWh) | Watts × Hours ÷ 1000 |
| Cost ($) | kWh × Rate ($/kWh) |
How much does a 1,500-watt space heater cost to run if it is on three hours a night? At 15 cents per kWh over 90 nights that is 405 kWh and $60.75, and the same arithmetic works for anything with a wattage on its label. This page has a single-device calculator, a multi-device list that adds up a household, and an energy converter for kWh, joules, BTU and therms.
Energy in kWh = watts × hours ÷ 1,000. Cost = kWh × rate in dollars per kWh. For a year, daily kWh is multiplied by the days you actually use the device. The monthly figure is daily kWh × (days per year ÷ 12), so it is an average month, not a specific one.
Using the page defaults of 1,000 W, 8 hours a day, 365 days and $0.13 per kWh: 1,000 × 8 ÷ 1,000 = 8 kWh a day, which costs $1.04. Over the year that is 2,920 kWh and $379.60. The monthly average is 8 × (365 ÷ 12) = 243.33 kWh, or $31.63.
In the multi-device list the starting rows are an air conditioner at 1,000 W for 8 hours on 120 days (960 kWh), a refrigerator at 150 W for 24 hours on 365 days (1,314 kWh) and ten LED lights at 100 W total for 5 hours on 365 days (182.5 kWh). The total is 2,456.5 kWh a year, about $319.35 at $0.13, or $26.61 a month.
What this does not account for: tiered or time-of-use rates, fixed monthly charges, demand charges and taxes. It treats the nameplate wattage as constant draw, so compressors that cycle, devices in standby, and loads that ramp up and down are all approximated by the wattage you type.
Divide the total amount on a recent bill by the kWh used. That folds delivery charges and fees into the rate. The per-kWh supply price printed on the bill alone will understate what a marginal kWh really costs.
The default of 150 W for 24 hours assumes the compressor never stops. A real refrigerator usually runs its compressor only part of the time, so treat the 1,314 kWh as an upper bound and lower the hours or wattage to match its energy label.
Watts and kilowatts measure power, the rate of use at a moment. A kilowatt-hour is energy: one kilowatt sustained for one hour. Utilities bill for kWh, which is why hours matter as much as wattage.
One kWh equals 1,000 Wh, 3.6 MJ, 3,600 kJ, about 3,412 BTU and about 859.85 kcal. The 'Calorie' rows are small calories, and a food Calorie is the kilocalorie.
Yes, through the days-per-year box. A pool pump used 150 days a year is entered as 150, and the monthly tile then spreads that over twelve months rather than showing the busy-season bill.
The box suggests a limit of 24, but it is only a hint. Entering a larger number will not be rejected, so keep an eye on it yourself.