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Calculators / Batteries and solar

Amp-hours to watt-hours

Put in the capacity off the battery label and its voltage. You’ll get watt-hours and amp-hours, the same battery at other voltages, and how long it runs a load.

Updated · How we check our numbers

These are example numbers. Put in yours.

Convert

Off the label: 100 Ah, 20,000 mAh or 1,024 Wh.

In
Battery voltage
W

Put in a load’s watts to see the ideal runtime.

Converted

1,200 Wh

100 Ah at 12 V is 1,200 watt-hours (1.2 kWh).

Watt-hours
1,200 Wh
Amp-hours
100 Ah100,000 mAh
Runtime at 60 W
20 hbefore losses

Estimate for planning only, not professional advice. Check the manufacturer’s instructions, your local code and a licensed professional before you buy, build or install. Use at your own risk. Terms.

Wh = 100 Ah × 12 V = 1,200 Wh

The same Ah at other voltages

Wh
  • 3.7 V100 Ah × 3.7 V
    370 Wh
  • 5 V100 Ah × 5 V
    500 Wh
  • 12 V100 Ah × 12 V
    1,200 Wh
  • 12.8 V100 Ah × 12.8 V
    1,280 Wh
  • 24 V100 Ah × 24 V
    2,400 Wh
  • 25.6 V100 Ah × 25.6 V
    2,560 Wh
  • 48 V100 Ah × 48 V
    4,800 Wh
  • 51.2 V100 Ah × 51.2 V
    5,120 Wh

Wh = Ah × volts. Same amp-hours at a higher voltage store more energy.

Use the nominal voltage

Use the voltage printed on the battery, not a charged reading. Power bank labels give mAh at the cell voltage and usually print the Wh too; the Wh figure is the one to trust.

Real runtime is shorter

1,200 Wh ÷ 60 W = 20 hours is the ideal. Running AC loads through an inverter loses some of that, and batteries stop before they’re fully empty, so plan on less. The power station runtime calculator builds that in.

Real runtime is shorter

1,200 Wh ÷ 60 W = 20 hours is the ideal. Running AC loads through an inverter loses some of that, and batteries stop before they’re fully empty, so plan on less.

How we work it out

A watt-hour is an amp-hour times the battery's voltage.

Wh = Ah × volts  ·  Ah = Wh ÷ volts  ·  Wh = mAh ÷ 1,000 × volts

So a 100 Ah battery at 12 V holds 1,200 Wh, and the same 100 Ah at 48 V holds four times as much. That's why amp-hours alone don't tell you how much a battery stores. Watt-hours do.

Runtime is watt-hours divided by the load's watts. That's the best case. An inverter loses some power turning DC into AC, and batteries shut off before they're completely empty, so real runtime is shorter.

Flying: the FAA limits lithium-ion batteries to 100 Wh each in carry-on. Up to two spares of 101 to 160 Wh need the airline's approval.

Where the numbers come from

Guides

Power

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