Use this page when a buyer asks how much energy a load uses over time. It is not a complete battery design. A battery project also needs usable depth of discharge, inverter efficiency, peak power, operating temperature, charging source, reserve margin and safety requirements.
What is the kW to kWh formula?
Multiply power in kilowatts by time in hours to estimate energy in kilowatt-hours.
Energy (kWh) = Power (kW) × Time (hours)For example, a 5 kW load running continuously for 4 hours uses 20 kWh of energy: 5 × 4 = 20. If the load is 500 W, convert it first: 500 W equals 0.5 kW, so 0.5 kW running for 6 hours uses 3 kWh.
Can you use a kWh result as the battery size?
No. A kWh result is the load estimate; the installed battery must also account for usable capacity and system losses.
| Input | Example | Why it changes the answer |
|---|---|---|
| Load | 5 kW | Determines instantaneous power demand |
| Run time | 4 hours | Determines energy use over the period |
| Base energy | 20 kWh | 5 kW × 4 h before losses or reserve |
| Inverter efficiency | 92% example assumption | More battery energy may be needed than the load alone |
| Usable battery window | 90% example assumption | Not all nominal battery capacity may be available |
With the two illustrative assumptions above, a 20 kWh load is not automatically a 20 kWh nominal battery. The exact design belongs to the system manufacturer and project engineer. The point of the calculator is to make the first conversation clearer.
What should a live calculator do?
A useful calculator accepts the inputs a buyer has, shows the formula and explains every assumption beside the result.
Use the calculator above for a first estimate. It accepts load in kW and hours, then returns the base energy estimate. It does not replace a system design.
Which questions should appear beside the result?
Show the questions that turn a simple arithmetic answer into a real design brief.
Ask whether the load is constant or intermittent, which loads must run at the same time, whether the system is grid-tied or off-grid, how many backup hours are required, what charging source is available and which location conditions apply. A calculator that hides these questions can create false confidence.
How do you account for efficiency and usable capacity?
Divide the load-energy estimate by the stated efficiency and usable-capacity assumptions, then label the result as an estimate.
For an illustrative case, a 20 kWh load, 92% inverter efficiency and 90% usable battery window gives a nominal-energy estimate of about 24.15 kWh: 20 ÷ 0.92 ÷ 0.90. This is arithmetic, not a guaranteed configuration. The actual result also changes with discharge rate, temperature, ageing, standby loads, charge source and the battery maker’s permitted operating window.
| Step | Example calculation | Meaning |
|---|---|---|
| Load energy | 5 kW × 4 h = 20 kWh | Energy demanded by the load |
| Inverter allowance | 20 ÷ 0.92 = 21.74 kWh | Energy needed before usable-capacity allowance |
| Usable-capacity allowance | 21.74 ÷ 0.90 = 24.15 kWh | Illustrative nominal storage estimate |
| Final engineering check | Use the exact manufacturer data | Confirms the actual system, not a generic formula |
Make the calculation transparent. A user should be able to see whether the page assumes 92%, 90% or another figure and change the assumption when their system data says otherwise. A calculator that gives one big green number without the inputs is a lead magnet, not a useful engineering tool.
What inputs should the calculator validate?
Validate non-negative numbers, unit choice and a realistic time period before showing a result.
The tool should state whether the input is W or kW, reject blank or negative entries, handle decimal values and show that 1,000 W equals 1 kW. It should also avoid calling the result a “recommended battery” unless an engineer has supplied an approved sizing method. For a B2B site, the useful next action is an enquiry form that carries the entered kW, hours, location and use case to a technical reviewer.
Related pages include battery systems, inverter choices, usable-capacity guidance and a sizing request. Those pages should include a return link such as “Need a quick kW to kWh estimate?” so the tool is part of a real content network.
Which inputs should be checked before using a calculator result?
Show the formula version, last review date and responsible technical reviewer beside the tool.
Unlike an opinion article, a calculator can create a confident-looking result from a small error. State the formula clearly, label every assumption and include a short note that the tool is for preliminary planning. When the formula changes, log the change and update the schema date.
What is a clear example a reader can check?
A 1.5 kW pump running for 8 hours uses 12 kWh before losses: 1.5 × 8 = 12.
Put one or two examples next to the tool so a reader can compare the output with visible arithmetic. Avoid an unexplained default value that looks like a project recommendation. The goal is to help a buyer ask a better question, not to replace system engineering.
Show the calculation line in the exported enquiry so the technical team can see how the visitor reached it.
That simple audit trail makes a tool easier to review, debug and improve after real enquiries arrive.
What should you include in a project enquiry?
Link the calculator to the relevant system, battery, inverter and project-enquiry pages using the buyer’s own terms.
Natural links include energy-storage systems, battery capacity and usable-energy guidance, inverter selection, battery safety and protection and a project sizing enquiry form. Those pages should link back to the calculator whenever a reader is working from kW and hours.
FAQ
Is 1 kW the same as 1 kWh?
No. kW is a rate of power, while kWh is the amount of energy used over time. A 1 kW load uses 1 kWh only when it runs for one hour.
How many kWh does a 2 kW load use in 3 hours?
It uses 6 kWh before losses: 2 kW × 3 hours. Add design assumptions separately for a battery project.
Why does an inverter change battery size?
An inverter consumes and loses some energy while converting power. Use the manufacturer’s efficiency data for the operating range.
Can this calculator size an entire solar system?
No. It creates a first energy estimate only. Solar production, weather, load profile, battery reserve and local code still need a system design.
Start a supplier conversation
Send a short project brief before asking for a final quote.
Include your target market, required specification, quantity and decision timing. It gives every supplier the same facts to answer.
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Share your target market, quantity and key requirements. A clear brief makes it easier to compare the replies you receive.
Reading: Energy Storage
Written by
Daniel Xu
Daniel writes supplier-comparison guides for industrial buyers, with a focus on quote scope, inspection evidence and delivery readiness.
Reviewed and updated 2026-07-16
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