Free tool
kW to kWh Calculator
Kilowatts are a rate; kilowatt-hours are an amount. Multiply the rate by the time — and keep the peak kW in view, because it is a separate limit.
kWh = kW × hours
kWh = kW × hours. 3 kW for 4 hours is 12 kWh; 2 kW for 45 minutes is 1.5 kWh. When the power changes, add each stretch: 7 kW for 2 hours then 3 kW for 1 hour is 17 kWh.
The same 17 kWh has a peak of 7 kW and an average of about 5.7 kW. Energy and peak power are two different limits. Starting from an appliance's watts, or from amps and volts, use the watts to kWh calculator.
The power and the time
One row for a steady load. If the power changes — a charger that tapers, a load that steps up and down — add a row for each stretch at a different kW.
Starting from watts, or from amps and volts? Use the watts to kWh calculator — it also handles duty cycle and cost.
The answer
Energy
12 kWh
kWh = kW × hours → 3 × 4
Peak power
3 kW
Average over 4 h
3 kW
Two different limits
The 12 kWh is the amount of energy — what a meter records, and what a battery would have to store to supply it. The 3 kW is the rate at its highest — what the supply, or an inverter, has to deliver at one moment.
What this does not tell you
Losses. Charging, inverting and storing energy each lose some of it; the kWh here is at the load. Motor surge. A motor starting draws well above its running kW for a moment. Your tariff. Some rate schedules bill peak demand in kW separately from energy in kWh — the utility's tariff sets how.
Informational use only, please verify before you rely on it
This reproduces the standard arithmetic relating power, time and energy (kWh = kW × hours), summed over steps of constant power, with the peak and time-weighted average power reported alongside. It is a preparation aid, not a measurement and not a determination. It does not apply charging, storage or inverter losses, read a utility tariff, or size batteries, inverters, conductors or overcurrent protection. Confirm with a meter, the equipment ratings and the utility's tariff.
This tool is provided for general informational and educational purposes only. Its output is an illustrative estimate generated from the values you enter and from general assumptions that will not match every deal, market, lender, or homeowner. It is not tax, legal, accounting, financial, or professional advice, and it is not a quote, an offer, a credit decision, or a guarantee of pricing, approval, timing, savings, or eligibility.
You are solely responsible for independently confirming all information presented here including any figures, rates, fees, margins, timelines, tax treatment, and federal, state, local, or utility incentives, with the applicable lender, authority having jurisdiction, and your own qualified tax, legal, and financial advisors before acting on it, relying on it, or presenting it to a homeowner or any third party. Incentive programs, lender terms, and permitting requirements change frequently and vary by jurisdiction.
Seamless Home is not a tax advisor, law firm, lender, or licensed installing contractor, and makes no representation or warranty as to the accuracy, completeness, or currency of the information produced by this tool. To the fullest extent permitted by law, Seamless Home accepts no liability for any decision made or action taken in reliance on it.
A rate and an amount, on the same spec sheet
Energy equipment is usually described with both units, and each answers a different question. A battery's kWh is how much it holds; its kW is how fast it can give it back. A charger's kW is its rate; the kWh it delivers depends on how long it runs. A house's bill is in kWh, while the question of whether everything can run at once is a kW question — the how many watts a house uses guide separates the two for a whole home.
That is why this calculator reports the peak next to the energy. Two load profiles can add up to the same kWh while one of them asks for twice the kW at its highest point, and equipment sized to the average would fall short at that moment. When a battery is part of the picture, its stored energy converts through the pack voltage with the watt-hours to amp-hours calculator, and the current behind a kW figure comes from the kW to amps calculator.
Frequently Asked Questions
How do you convert kW to kWh?+
Multiply the kilowatts by the hours: kWh = kW × hours. A 3 kW load running 4 hours uses 12 kWh. For minutes, divide by 60 first — 2 kW for 45 minutes is 2 × 0.75 = 1.5 kWh.
How many kWh is 1 kW?+
There is no single answer, because a kilowatt is a rate and a kilowatt-hour is an amount. 1 kW for 1 hour is 1 kWh; for 30 minutes it is 0.5 kWh; for 24 hours it is 24 kWh. The conversion needs a time.
What is the difference between kW and kWh?+
kW measures power — how fast energy is being used or delivered at a moment. kWh measures energy — how much was used over a period. It is the difference between speed and distance: 3 kW for 4 hours is 12 kWh, just as 3 miles an hour for 4 hours is 12 miles.
How do I work out kWh when the power changes?+
Split the run into stretches at a steady power, multiply each by its time, and add them. 7 kW for 2 hours then 3 kW for 1 hour is 14 + 3 = 17 kWh. The calculator does this with up to six steps and also shows the peak and the average kW.
How is this different from the watts to kWh calculator?+
Watts to kWh starts from one appliance's watts — or amps and volts with a power factor — and adds duty cycle and an optional electricity rate. This page starts from kilowatts, handles a load that steps between levels, and puts the peak kW next to the energy.
Why does a home battery have both a kW and a kWh rating?+
Because they are separate limits. The kWh rating is how much energy it stores; the kW rating is how much power it can deliver at once. A battery with plenty of kWh can still fail to run a load whose peak kW is above its power rating, and a battery with a high kW rating runs out sooner if its kWh is small.
Is this a determination?+
No. It reproduces the arithmetic relating power, time and energy as a preparation aid. It does not measure a load, apply charging or inverter losses, read a tariff, or size a battery, an inverter, conductors or protection. Confirm with a meter, the equipment ratings and the utility's tariff.
Related resources
Watts to kWh Calculator
Energy from one appliance's watts or amps, with duty cycle and cost.
Learn more →kW to Amps Calculator
The current behind a kilowatt figure, with power factor.
Learn more →Watt Hours to Amp Hours Calculator
Stored energy converted through the battery voltage.
Learn more →Critical Load Panel Planner
Which circuits a home battery can actually keep running.
Learn more →Power and energy, read as separate limits
Seamless Home runs the design, permit and interconnection layer for the partners it works with — where a kW rating and a kWh rating get read as the different figures they are. Coverage is confirmed per service area rather than promised as blanket availability.
Get In Touch