Electricity Cost Calculator

The electricity cost formula

Every electricity bill comes from one calculation. The appliance's power rating in watts is divided by 1,000 to get kilowatts, multiplied by the hours it runs, and multiplied by your tariff:

cost = watts ÷ 1000 × hours × price per kWh

A 100 W lamp running 5 hours a day uses 0.5 kWh daily. At the US average of 18.34¢ per kWh that is 9.2 cents a day, $2.75 a month, and $33 a year — from one bulb.

kW and kWh are not the same thing

This is the distinction the whole subject turns on. Kilowatts measure rate — how fast something draws power right now. Kilowatt-hours measure quantity — how much energy it consumed over time.

Speed and distance is the exact analogy: kW is the speedometer, kWh is the odometer. A 2 kW heater running for 30 minutes uses 1 kWh; the same heater running 3 hours uses 6 kWh. The kW never changed. You are billed for kWh, which is why runtime matters more than the rating on the label.

On a bill, a "unit" is one kilowatt-hour — the two words mean the same thing.

Average residential electricity price by state

Your own tariff is printed on your bill and is always the better number to use. These are the state averages across all residential customers, which is the right figure when you are comparing states rather than plans.

June 2026, cents per kilowatt-hour, with the same month a year earlier for comparison. Source: U.S. Energy Information Administration, Electric Power Monthly, Table 5.6.A, released 26 August 2026. Figures checked 17 September 2026.

The spread is the headline. Hawaii at 52.72¢ is 4.0 times Nevada at 13.11¢ — the same appliance, the same hours, a bill 302% larger for no reason a household controls. Prices rose year on year in 46 of the 51 jurisdictions listed — the 50 states plus the District of Columbia — and fell in 5.

Two cautions about averages. They blend every rate plan in the state, so a household on a time-of-use tariff can pay well above or below the figure here depending on when it runs things. And they include fixed charges spread across consumption, which means a low-usage home's effective rate per kWh is higher than the state average and a high-usage home's is lower.

What common appliances cost to run

At the US average of 18.34¢ per kWh. Every row is just the formula above, so you can swap in your own tariff and rating — check the plate on the appliance, because ratings vary widely by model and age.

The fridge row is the one worth reading twice. A compressor rated at 150 W does not draw 150 W all day — it cycles, and the duty cycle is what sets the bill. Rating a fridge at its plate figure overstates its running cost roughly threefold, which is why appliance labels quote kWh a year rather than watts.

The pattern across the rest is consistent: anything that makes heat dominates the bill. The heater costs more in four hours a day for one winter than the television does running five hours a day all year, because heating is measured in kilowatts while electronics are measured in watts.

What a typical home uses

The average US residential utility customer bought 10,791 kWh in 2022, about 899 kWh a month (EIA). At 18.34¢ that is roughly $1,979 a year before fixed charges and taxes. UK homes run far lower at about 2,700 kWh a year, largely because heating and hot water are usually gas rather than electric.

Because usage varies by a factor of three and rates vary by a factor of 4.0, a national average bill tells you very little. Your own tariff is on your bill, and it is the only number worth putting into the calculator.

Reading an appliance label

Rating plates state the maximum draw, not the average. A fridge labelled 150 W does not use 150 W continuously — its compressor cycles, so real consumption might average 40–50 W over a day. A kettle labelled 3 kW genuinely draws 3 kW, but only for the two minutes it is boiling.

Note the ordering. The kettle has the highest rating in the list and one of the lowest annual totals. The heater is the opposite. A high kW rating is only expensive if it runs for a long time.

Batteries, solar, and the units that get mixed up

A 10 kWh battery rated at 5 kW output can run 5 kW of load for two hours, or 1 kW of load for ten. Both numbers are needed and neither implies the other. Buying on capacity alone leaves you unable to run the oven; buying on output alone leaves you out of power by midnight.

kWp on a solar quote is peak capacity in laboratory conditions, not output. A 4 kWp array in the UK produces roughly 3,400 kWh a year — about 850 kWh per kWp installed. In Arizona the same array produces nearly double. The ratio between them is the capacity factor, and it is what the quote should really be telling you.

Amp-hours need a voltage before they mean anything. A 100 Ah battery is 1.2 kWh at 12 V and 4.8 kWh at 48 V — same amp-hours, four times the energy. Compare batteries in kWh, never in Ah.

Converting kWh to other energy units

Amp-hours need a voltage. A kWh is energy; an amp-hour is charge. They only convert once you know the system voltage, which is why a 100 Ah battery is 1.2 kWh at 12 V but 4.8 kWh at 48 V.

Gas in kWh and m³ works the other way: gas meters read cubic metres, and suppliers convert to kWh using a calorific value, roughly 1 m³ ≈ 10.5 kWh for UK natural gas.

kVA, kVAh, and three-phase supplies

On commercial supplies you will meet kVA (apparent power) alongside kW (real power). The ratio between them is the power factor:

kW = kVA × power factor

Domestic customers pay for kWh only. Commercial tariffs often bill kVAh as well, penalising a poor power factor, which is why industrial sites install correction equipment. For sizing a supply, the formulas are:

The √3 (about 1.732) is what makes three-phase supplies carry substantially more power over the same conductors.

Comparing running costs against a car journey? The fuel cost calculator works out trip costs the same way. To see what a rate rise means in percentage terms, use the percentage change calculator.