kW to kWh Calculator

What a kilowatt-hour adds to a kilowatt

A kilowatt tells you how fast a device draws power, and a kilowatt-hour tells you how much energy it used. The second unit is the first unit multiplied by hours, which is why the letter h sits at the end. A 1 kW device that runs for one hour uses 1 kWh, and the same device for 30 minutes uses 0.5 kWh.

The formula is short, and every version of this calculator is built from it:

• kWh = kW × hours
• kW = kWh ÷ hours
• hours = kWh ÷ kW

Worked example: a 2 kW space heater on for 6 hours a day uses 2 × 6 = 12 kWh a day, which is 360 kWh in a 30 day month. At the August 2026 U.S. residential average of 18.16 cents per kWh, that month costs 360 × $0.1816 = $65.38.

A second example runs the other way. A window air conditioner that used 90 kWh last month and ran about 150 hours averaged 90 ÷ 150 = 0.6 kW while it was on. The utility bills the kWh, but the kW rating is what decides whether the breaker and the wiring can carry the load.

The same formula read three ways

Most mistakes with this conversion come from using the wrong side of the equation, so it helps to keep all three forms in view. Energy is power times time, power is energy divided by time, and time is energy divided by power. The time unit must be hours, not minutes or days, or the answer lands off by a factor of 60 or 24.

Example one: a household that used 600 kWh in a 30 day month of 720 hours averaged 600 ÷ 720 = 0.83 kW around the clock. Example two: the average U.S. home uses about 10,500 kWh a year, according to the EIA electricity use in homes page, which works out to 10,500 ÷ 8,760 = 1.20 kW of average draw. Example three: a 1.5 kW kettle asked for 1.5 kWh needs 1.5 ÷ 1.5 = 1 hour, which is longer than any kettle runs, and that mismatch is a useful warning that the numbers were assigned to the wrong device.

The third form answers a scheduling question. If a 7.2 kW car charger must deliver 36 kWh, it needs 36 ÷ 7.2 = 5 hours on the charger, so an overnight window of 8 hours leaves room for a top-up rather than a full charge from empty.

kW to kWh chart for common household loads

The table multiplies each load's kW by its daily hours, then by 30 for a month and 365 for a year. The cost column applies 18.16 cents per kWh, the U.S. residential average for August 2026.

Check one row by hand: the space heater at 1.5 kW for 6 hours gives 9 kWh a day, 9 × 365 = 3,285 kWh a year, and 3,285 × $0.1816 = $596.56. The refrigerator row uses an average draw of 55 W instead of the 150 W it pulls while the compressor runs, because a fridge cycles on and off. Counting the compressor rating for all 24 hours would overstate its yearly use by roughly three times.

That gap between nameplate power and average power is the largest single source of inflated estimates. A device rated 1,500 W does not draw 1,500 W for every second it is plugged in, and a pump or compressor that runs half the time uses half the energy its rating suggests.

What a kilowatt-hour costs in 2026

Rates differ by state and by season, so treat any single figure as a national average rather than your bill. The EIA Electric Power Monthly table 5.6.A puts the U.S. residential average at 18.16 cents per kWh for August 2026, up from 17.57 cents in August 2025. The same table shows Hawaii at 47.18 cents and North Dakota at 13.31 cents, a spread of more than three to one.

At that average, the typical 10,500 kWh household year costs 10,500 × $0.1816 = $1,906.80, or $158.90 in an average month. A 1,500 W space heater run 6 hours a day for 30 days adds 270 kWh and $49.03. The arithmetic is the same at every scale, and the only input that changes with location is the rate in the final multiplication.

Time-of-use plans price the same kWh differently depending on the hour, so shifting a load from 6 p.m. to 11 p.m. can change the bill without changing the kWh at all. The conversion to energy stays fixed; only the price applied at the end moves.

Nameplate kW is not always the kW you pay for

A motor nameplate lists shaft output, not electrical input. Divide the output by efficiency to get the power the meter sees, then divide by power factor to get the kVA the wiring must carry. A 7.5 kW motor at 89% efficiency draws 7.5 ÷ 0.89 = 8.43 kW from the line, and at a power factor of 0.85 that is 8.43 ÷ 0.85 = 9.92 kVA.

Run that motor 8 hours a day for 20 working days and the energy is 8.43 × 160 = 1,348 kWh, or $244.85 at 18.16 cents. An estimate built on the 7.5 kW nameplate would have said 1,200 kWh and missed about 12% of the bill. Inverter-driven appliances add another layer, because their nameplate may list maximum output rather than the draw a typical day produces.

For resistive loads such as a kettle, an incandescent bulb or a space heater, nameplate kW and input kW are the same number and the power factor is 1.0. The correction only matters for motors, compressors, pumps, and anything with a switching supply. When a spec sheet gives only kVA, multiply by the power factor to get kW before converting to energy, and the NIST guide to SI units is the reference for how the watt and the kilowatt-hour are defined.

Demand charges and load factor on a commercial bill

Business tariffs often charge for kWh and for the highest kW reached during the month. A shop that peaks at 50 kW and pays $12 per kW in demand charges adds $600 to the bill before a single kWh is priced. If the same shop uses 12,000 kWh in a 730 hour month, its load factor is 12,000 ÷ (50 × 730) = 0.329, or 32.9%.

Load factor is the bridge between the two units: it reports how much of the peak capacity the site used on average. Spreading the same 12,000 kWh across more hours lowers the peak, and a peak of 35 kW instead of 50 kW would cut the demand charge to $420 while leaving the energy charge untouched. That is why battery storage and schedule shifting show up on commercial bills even when total kWh does not change.

To turn a demand reading into energy, multiply by the hours held at that demand, and remember that demand is a 15 or 30 minute average rather than an instant reading. A 50 kW peak held for 15 minutes is 12.5 kWh, a small amount of energy attached to a large charge.

Turning a bill back into kilowatts and hours

The reverse direction is just as useful when a bill looks high. Divide the dollar amount by the rate to get kWh, then divide by the hours in the period to get the average kW. A $150 bill at 18.16 cents is 150 ÷ 0.1816 = 826 kWh, and over a 720 hour month that is 826 ÷ 720 = 1.15 kW of average draw.

Compare that average with the big loads in the house. One 4.5 kW water heater running 3 hours a day averages 0.56 kW on its own, roughly half of the whole household average. Two such appliances explain a bill that seemed impossible, while a house with no large loads and a 1.15 kW average points to something running when nobody is home.

The same arithmetic sizes a backup battery. A 10 kWh battery covering 1.2 kW of average load lasts 10 ÷ 1.2 = 8.3 hours, though usable capacity is usually 90% of the nameplate, which brings it to about 7.5 hours. Conversions in this direction always run through the same three quantities, so a page of kWh figures can be turned into a kW profile with a division per row.

Where kW to kWh conversions go wrong

Four slips account for most bad answers:

• Watts mixed with kilowatts. A 1,500 W heater is 1.5 kW. Entering 1,500 as kW multiplies the answer by 1,000.
• Assuming 24 hours at full power. Few loads run at nameplate all day. Use a duty cycle, or measure the average with a plug-in monitor, as the Department of Energy guide describes.
• Forgetting charging losses. An EV that stores 36 kWh pulls about 40 kWh from the wall at 90% efficiency, so the meter bills 40 kWh.
• Multiplying days by 30 for a calendar month. February and August differ by about 10%, enough to explain a bill that looks wrong.

A sanity check closes the loop: 1 kW running flat out for a full year is 8,760 kWh, which at 18.16 cents is $1,590. A household total far above that with no EV, heat pump or pool points to a unit error somewhere in the chain, not to a faulty meter.

Keep the units on the page while you work. Writing kW next to the power, h next to the time and kWh next to the result prevents the one error that survives every other check, which is a correct multiplication of the wrong numbers.