mAh to kWh: How to Convert Battery Capacity

How do you convert mAh to kWh?

Multiply the mAh by the voltage, then divide by one million. kWh = (mAh times volts) divided by 1,000,000. It is easier to do in two steps. First get watt-hours: Wh = mAh times volts, divided by 1,000. Then divide watt-hours by 1,000 to get kWh. A 20,000 mAh power bank at its usual 3.7 volts is 20,000 times 3.7, or 74,000, divided by 1,000 for 74 Wh, then divided by 1,000 again for 0.074 kWh.

In practice most people converting a power bank want watt-hours, not kWh, because a single bank is a tiny fraction of a kilowatt-hour. Nobody says a 0.074 kWh power bank; they say 74 Wh. kWh is the scale for home batteries and power stations, where a unit might hold 1 to 20 kWh. If the difference between power and energy is fuzzy, the kW vs kWh explainer covers it. To go the other way, from kWh back to mAh, you use the same formula rearranged, which is further down.

Why do you need the voltage to convert mAh?

Because mAh measures charge, not energy, and energy equals charge multiplied by voltage. A milliamp-hour tells you how much current a battery can push and for how long, which is capacity of charge. A watt-hour or kilowatt-hour tells you how much work that charge can do, which is charge times the voltage it is delivered at. Two batteries with the same mAh but different voltage hold different amounts of energy, so an mAh number by itself tells you almost nothing about how long a battery will run something.

The voltage to use depends on the battery. Lithium-ion cells in phones and power banks are about 3.6 to 3.7 volts each, and that single-cell 3.7 volts is what a power bank's mAh rating is measured at, so use it for them. LiFePO4, the chemistry in most solar batteries, is about 3.2 volts per cell (see LiFePO4 vs lithium-ion). Battery packs wire cells in series up to 12, 24, or 48 volts, so for a labeled 12V or 48V pack you use that pack voltage, not 3.7. Get the voltage wrong and your energy number is off by the same ratio.

What is 10,000 mAh or 20,000 mAh in watt-hours?

At the standard 3.7 volts a power bank is quoted at: 5,000 mAh is about 18.5 Wh, 10,000 mAh is about 37 Wh, 20,000 mAh is about 74 Wh, 27,000 mAh is about 100 Wh, 50,000 mAh is about 185 Wh, and 100,000 mAh is about 370 Wh. Divide any of those Wh figures by 1,000 for kWh, so even a big 50,000 mAh bank is only 0.185 kWh, a fraction of what a house draws in a single hour.

That 100 Wh mark is worth remembering. A 27,000 mAh bank at 3.7 volts lands right at 100 watt-hours, which is the limit airlines let you carry on without asking, so you see a lot of banks capped near 24,000 to 27,000 mAh for that reason. Banks rated 50,000 mAh and up sit in the 100 to 160 Wh range that needs airline approval, or above 160 Wh, which is barred from planes entirely. The watt-hour figure, not the mAh, is what the airline rule is written in.

This is also why big storage never gets labeled in mAh. A power station holding 1,000 Wh would be a meaningless 270,000 mAh if it copied the power-bank style, so manufacturers rate stations and home batteries in Wh and kWh instead. When you compare a bank to a station, put both in watt-hours first.

Why doesn't a 20,000 mAh power bank charge my phone six times?

Because the bank's mAh is rated at its internal 3.7 volts, but it charges your phone at 5 volts over USB, and converting between the two wastes energy. A 20,000 mAh bank holds about 74 Wh. A phone battery is roughly 3,000 to 5,000 mAh at about 3.85 volts, or about 12 to 19 Wh. On paper 74 divided by 15 looks like five charges.

In the real world the boost from 3.7 volts up to 5 volts, then back down to your phone's voltage, plus heat, loses roughly 20 to 35 percent. So a 20,000 mAh bank delivers about 55 to 60 Wh of usable output and gives most phones about 2.5 to 3.5 full charges, not five or six. Stated as capacity at the 5 volt output, a 10,000 mAh bank is really only about 6,000 to 6,500 mAh. When you shop, compare banks at the same voltage, and treat any charge-count claim on the box as a best case. Our best solar power banks guide sorts picks by real usable capacity for this reason.

How do you convert kWh or Wh back to mAh?

Rearrange the formula: mAh = kWh times 1,000,000, divided by volts (or mAh = Wh times 1,000, divided by volts). The voltage still decides everything. 1 kWh at 3.7 volts is about 270,000 mAh, but the same 1 kWh at 12 volts is about 83,000 mAh, and at 48 volts about 20,800 mAh. Same energy, wildly different mAh, which is exactly why nobody labels large batteries this way.

One more unit to keep straight: 1 Ah equals 1,000 mAh. Solar and RV batteries are usually rated in amp-hours (Ah) at a pack voltage, so a 12V 100Ah battery is 100,000 mAh at 12 volts, which is 100 times 12, or 1,200 Wh (1.2 kWh). That is a real, useful amount of storage, and what a 100Ah battery can run walks through the runtimes. The lesson is the same in both directions: pin down the voltage first, then the numbers behave.

How does converting mAh apply to solar?

For solar you mostly work in Wh and kWh, because that is what panels produce and what your electricity bill counts. A solar battery's storage is in kWh, your daily use is in kWh, and a panel's daily output is in kWh. Milliamp-hours only show up on the small gear, power banks and phone-charging panels, so when you size a home or off-grid system you can ignore mAh entirely and stay in kilowatt-hours. To match a panel array to your real kWh use, run your numbers through the solar panel calculator.

The one time the conversion earns its keep is comparing a small phone bank to a portable power station. Put both in watt-hours: a 20,000 mAh phone bank is about 74 Wh, while a small power station is usually 300 to 1,000 Wh, so the station holds roughly 4 to 13 times more energy. Same unit, honest comparison, and no marketing mAh to trip over.

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