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Battery & storage
Battery kWh to runtime converter
Enter your battery's kWh capacity and the load you're running. Get a straightforward runtime conversion in hours.
How it works
Three steps to a runtime conversion
Step 1
Enter your battery's nameplate rating
This figure is printed on the unit's spec sheet. The usable vs nameplate calculator explains why this number differs from what you can actually use.
Step 2
Enter your load
Use the total running watts of whatever you're powering. The backup runtime estimator handles more complex, mixed load scenarios if a single load figure isn't enough.
Step 3
Apply depth of discharge and efficiency
These two factors together typically reduce usable energy by 10 to 20% below nameplate. Skipping them would overstate your real runtime.
Understanding the kWh to runtime conversion
The math behind the conversion
Runtime in hours equals usable energy in kWh divided by load in kW. Usable energy is the battery's nameplate kWh multiplied by depth of discharge and round trip efficiency, both of which reduce the energy actually available below the rated nameplate figure. Skipping these two factors and dividing nameplate kWh directly by load overstates real-world runtime, sometimes significantly. The usable vs nameplate calculator breaks down exactly how much smaller usable capacity is for a given battery, and the depth of discharge vs cycle life calculator in our Battery Chemistry & Storage category shows how the depth of discharge figure itself varies by chemistry.
Why this conversion assumes a constant load
This calculator treats the load as continuous and unchanging for the entire runtime, which is a simplification. Real household loads often cycle, like a refrigerator compressor turning on and off, which means actual runtime can be somewhat longer than this conversion suggests for loads that don't run continuously, consistent with duty-cycle guidance from the ENERGY STAR appliance efficiency program. The backup runtime estimator is built around the same math but frames it specifically around household backup scenarios.
Common conversion reference points
A standard 13.5 kWh home battery running a typical critical loads circuit of 500 to 800 watts provides roughly 14 to 22 hours of runtime after depth of discharge and efficiency losses, figures in line with the 85% round trip efficiency NREL uses as its representative baseline for residential systems in its Annual Technology Baseline. The same battery running a heavier whole-home load of 3 kW or more drops to under 4 hours, illustrating how much load size drives this calculation. The battery storage size calculator works this same math in reverse, starting from a target runtime instead of a fixed battery size.
What to do with this number next
If you're going the other direction, starting from a target runtime and solving for battery size, the runtime to battery kWh converter handles that calculation directly. If you're comparing this runtime against a financed system's payback timeline, the cash flow positive timeline calculator in our Financing category covers that separate question.
Questions
Frequently asked
Multiply the battery's nameplate kWh by depth of discharge and round trip efficiency to get usable kWh, then divide by your load in kilowatts. A 13.5 kWh battery at 90% depth of discharge and 92% efficiency running a 1,000 watt load lasts about 11.2 hours.
Dividing nameplate kWh directly by load in kW overstates runtime, since it ignores depth of discharge limits and round trip efficiency losses that both reduce the energy actually available to the load. Including both factors gives a more accurate real-world runtime figure.
Yes, this converter assumes the load stays constant for the full runtime, which is a simplification since most household loads cycle on and off. Use the backup runtime estimator for a load list with mixed continuous and cycling appliances.
A standard 13.5 kWh home battery running a typical 500 to 800 watt critical loads circuit provides roughly 14 to 22 hours of runtime after depth of discharge and efficiency losses, depending on the exact battery and load specifications.