mAh to Wh Calculator

To convert mAh to Wh, multiply the milliamp-hours by the pack’s nominal voltage, then divide by 1,000. A 20,000mAh power bank on 3.7V lithium cells holds 74Wh. Use the cell voltage printed on the battery, not the 5V its USB port delivers — that single substitution inflates the answer by 35%.

The mAh to Wh formula, explained

Three terms, and only one of them causes trouble.

Wh = (mAh × V) ÷ 1,000

• mAh — milliamp-hours. Charge, not energy. A 2,000mAh cell pushes two amps for an hour, or one amp for two. On its own it says nothing about how much work the battery can do, because it says nothing about the voltage.
• V — volts. The pack’s nominal voltage: the average it holds across a discharge, not the figure it reads straight off the charger. This term decides the answer, and it is the one nobody quotes.
• Wh — watt-hours. Energy. One watt-hour runs a one-watt load for one hour, and unlike mAh it compares honestly between batteries of any voltage or chemistry.

The 1,000 is only the milli- prefix coming off. If your figure is already in amp-hours, skip that step: 5Ah × 12V = 60Wh.

Conversion table: milliamp-hours to watt-hours

Three voltages cover almost everything a reader is holding: 3.7V for the lithium-ion cells in phones, tablets and power banks, 12V for lead-acid and AGM, 12.8V for a 12V LiFePO4 drop-in.

The 26,800mAh row is the largest common power-bank size still under 100Wh at 3.7V, the airline carry-on threshold; the exact line is 27,027mAh. The bottom row is the argument for watt-hours: the same 100,000mAh is 370Wh in a phone-cell pack and 1,280Wh in a 12V lithium battery. An mAh figure quoted without a voltage ranks nothing.

Why this conversion matters for portable power and solar

There is a hard line through this market at about 100Wh. Below it, everything is sold in mAh: power banks, phone batteries, camera cells, tool packs. Above it, everything is sold in Wh: portable power stations, solar generators, home batteries. Two units for the same physical thing, and nothing compares across the line until you convert.

• How many times will this station charge that device? A 20,000mAh bank holds 74Wh, so a 1,000Wh station has an arithmetic ceiling of thirteen charges. Derate to 850Wh usable, allow 85–95Wh at the socket per charge, and the honest answer is about nine. Our guide to what size power station you need builds the same sum from a load list.
• How big a bank does the van need? Deep-cycle batteries are rated in amp-hours — the same unit, a thousand times larger. A 100Ah LiFePO4 battery is 100,000mAh, or 1,280Wh at 12.8V. With the load list in watt-hours, watt-hours to amp-hours converts it back.
• Will the panels refill what I drew? Panels are rated in watts, and watts × usable sun hours gives watt-hours; milliamp-hours cannot be divided into watts. A 400W array over four sun hours is 1,600Wh gross, roughly 1,280Wh after controller and cable losses — one 100Ah 12.8V battery. Our solar sizing guide and solar battery calculator work in watt-hours.

Which voltage belongs in the formula

Nominal voltage is a stated average, not a measurement. A lithium-ion cell leaves the charger at about 4.2V and is flat at roughly 3.0V; 3.7V is the middle of that curve and what the rating was measured against. Using the 4.2V a meter reads on a full cell overstates capacity by about 14%. One shortcut: at any voltage, 1,000mAh is worth exactly that many watt-hours, so the voltage column doubles as the multiplier.

The 3.6V and 3.7V rows sit under 3% apart, enough to explain a small mismatch with a spec sheet but not to change a decision. The series voltages are unforgiving: a laptop pack read as 3.7V rather than 11.1V is wrong by a factor of three. If the label prints a watt-hour figure outright, use it.

Worked examples and the airline limit

• A 10,000mAh pocket bank. 10,000 × 3.7 ÷ 1,000 = 37Wh.
• A 24,000mAh travel bank. 24,000 × 3.7 ÷ 1,000 = 88.8Wh, inside the 100Wh carry-on allowance.
• A 5,000mAh laptop battery at 11.1V. 5,000 × 11.1 ÷ 1,000 = 55.5Wh, which is why a 500Wh station gives seven or eight laptop charges, not fifty.
• A 5.0Ah cordless tool pack at 18V nominal. 5,000 × 18 ÷ 1,000 = 90Wh, more energy than most power banks.
• A 15Ah e-bike battery at 36V. 15,000 × 36 ÷ 1,000 = 540Wh, which is also why it cannot fly.
• A 100Ah 12V LiFePO4 battery. 100Ah is 100,000mAh, so 100,000 × 12.8 ÷ 1,000 = 1,280Wh, nearly all usable.

Going the other way, mAh = (Wh × 1,000) ÷ V, is the Wh to mAh calculator. At battery-bank scale, drop the three zeros and work in amp-hours instead.

The airline rule is the most common everyday reason to run this conversion: it is written in watt-hours, the battery is labelled in milliamp-hours. Spares travel in carry-on only. Under 100Wh they need no approval; 100–160Wh needs the airline’s permission, usually two spares; above 160Wh they are barred outright. The practical ceiling is a bank rated at or below 27,000mAh, and a printed Wh figure on the casing beats a computed one at a security desk.

What the pack holds vs what you get out

The conversion tells you what the pack contains. What reaches the device is less, because stepping 3.7V cells up to a 5V USB output costs energy. At 85–90% efficiency, a 20,000mAh bank holding 74Wh delivers 63–67Wh; a 5,000mAh phone battery at 3.85V is about 19Wh, so that is three full charges, not the four the mAh figures imply.

The same effect decides how you charge from a power station. DC or USB-C straight from the unit is one conversion; the AC inverter into a wall brick is two, and costs 10–15% more for no benefit. The comparison tool lists capacity and ports side by side.

Frequently asked questions