Your numbers
1
Target runtime and load
2
Battery characteristics
Battery & storage
Runtime to battery kWh converter
Enter your target runtime and load. Get the battery kWh capacity you'd need to hit that target.
How it works
Three steps to a battery capacity conversion
Step 1
Set your target runtime
Decide how many hours of coverage you actually want. The 24 hour backup tool uses a fixed common target if you want a dedicated breakdown. The hybrid inverter sizing calculator checks whether your inverter can handle this result.
Step 2
Enter your combined load
Add up running watts for everything you want powered. The critical loads calculator handles a detailed appliance-by-appliance breakdown.
Step 3
Round up to a real battery size
Batteries come in fixed nameplate sizes, so your calculated figure will round up. The battery count vs autonomy tool handles this rounding step.
Understanding the runtime to kWh conversion
The math behind the conversion
Nameplate kWh needed equals your load in kW multiplied by target hours, then divided by depth of discharge and round trip efficiency together. This second step matters because a battery's rated capacity is always larger than what's actually usable, a gap NREL accounts for in its 85% round trip efficiency baseline in the Annual Technology Baseline, so working backward from a target runtime requires inflating the raw energy figure to account for that gap. Skipping this step, and sizing only to the raw usable energy figure, would leave you short of your actual target once real-world losses are applied.
Why combining multiple loads into one figure works here
This converter treats your input as a single combined load, which is accurate as long as you've added up every appliance you want powered simultaneously before entering the number. If you'd rather work from a detailed appliance list instead of a single combined figure, the critical loads calculator and whole home backup tool both let you check off individual loads and total them automatically, using wattage references similar to those published by ENERGY STAR's appliance efficiency database.
Why the result almost always rounds up
Batteries are manufactured and sold in fixed nameplate sizes, most commonly 10 to 13.5 kWh per unit, so a calculated figure like 14.5 kWh means buying at least one full battery, and likely two if your unit size is smaller than that figure. The battery count vs autonomy tool handles this final rounding step and shows the resulting battery count directly.
What to do with this number next
Once you have a target nameplate capacity, the cost per kWh comparison tool shows what different battery brands charge for that amount of capacity, and the hybrid inverter sizing calculator in our Inverters & Equipment category confirms your inverter can actually deliver your target load. If you're financing the resulting battery size, the loan payment calculator in our Financing category shows the monthly cost.
Questions
Frequently asked
Multiply your load in kilowatts by the target hours to get usable kWh needed, then divide by depth of discharge and round trip efficiency to get the nameplate kWh required. A 1,000 watt load for 12 hours needs about 14.5 kWh of nameplate battery capacity.
Depth of discharge and round trip efficiency both reduce how much of a battery's rated capacity is actually usable, so the nameplate rating needs to be larger than the raw energy calculation to account for that gap. Skipping this step would undersize the battery.
This converter uses a single combined load figure, so add up the running watts of everything you want powered before entering it. For a more detailed breakdown across multiple named appliances, the critical loads only calculator handles that directly.
Yes, since batteries are sold in fixed nameplate sizes, most commonly 10 to 13.5 kWh per unit, your calculated figure almost always rounds up to the next whole battery. The battery count vs autonomy tool handles this rounding step directly.