Multiply amp-hours by voltage to get watt-hours: Wh = Ah × V. A 100Ah battery holds 1,280Wh at a nominal 12.8V and 5,120Wh at a nominal 51.2V — four times the energy from the identical Ah rating, because amp-hours describe current capacity only. Without a voltage attached, an Ah figure tells you nothing about how much energy you actually have.
The formula, both directions
Watt-hours and amp-hours convert into each other with one multiplication or one division:
- Wh = Ah × V (amp-hours to watt-hours)
- Ah = Wh / V (watt-hours to amp-hours)
Worked forward: a 50Ah battery at 12.8V nominal is 50 × 12.8 = 640Wh. Worked backward: a power station rated at 1,024Wh running on a 51.2V pack has 1,024 / 51.2 = 20Ah of capacity. Same battery, two ways of describing it — and only one of them, Wh, tells you how much you can actually run and for how long. If you only need one direction, the site has standalone tools for it: amp-hours to watt-hours and watt-hours to amp-hours.
Why an Ah number alone is meaningless
This is the single most common error in battery shopping. Two batteries can both be labeled “100Ah” and differ by a factor of four in stored energy, because the voltage behind the label is different. A 12V lead-acid deep-cycle battery, a 12V LiFePO4 pack, and a 48V LiFePO4 pack can all carry a “100Ah” sticker. Their watt-hours are not remotely the same:
| Capacity | Nominal voltage | Watt-hours |
|---|---|---|
| 10Ah | 12.8V (LiFePO4, 4 cells) | 128Wh |
| 50Ah | 12.8V | 640Wh |
| 100Ah | 12.8V | 1,280Wh |
| 100Ah | 25.6V (LiFePO4, 8 cells / “24V” class) | 2,560Wh |
| 100Ah | 51.2V (LiFePO4, 16 cells / “48V” class) | 5,120Wh |
| 20,000mAh (20Ah) | 3.7V (lithium-ion power bank cell) | 74Wh |
Every row from 10Ah to the 100Ah/51.2V row scales in exact proportion to voltage, because the Ah figure hasn’t changed at all — only what it’s multiplied by has. That’s why any spec sheet, listing, or forum post that states an Ah number without a voltage next to it is giving you half an answer. Ask for the voltage, or the Wh, before you compare two batteries on capacity.
Nominal voltage versus rated voltage
The V in Wh = Ah × V should be the nominal voltage, not the voltage on a fully-charged multimeter reading. Nominal voltage is the average voltage a cell holds across most of its discharge curve, and it’s what manufacturers use to calculate the Wh figure printed on a label. A LiFePO4 cell has a nominal voltage of 3.2V. Wire four in series and you get a nominal 12.8V pack (commonly sold as “12V”); eight in series gives nominal 25.6V (“24V”); sixteen in series gives nominal 51.2V (“48V”). A freshly charged LiFePO4 cell can read closer to 3.4-3.6V on a meter, and a 12V lead-acid battery at full charge reads nearer 12.6-12.8V rather than exactly 12V — but the nominal figure is what the Wh math is built on, and it’s the number to use.
Why batteries are sold in Ah and power stations in Wh
A standalone deep-cycle or LiFePO4 battery is a component: it might end up wired at 12V, 24V, or 48V depending on the system it’s dropped into, so the manufacturer states Ah at whatever nominal voltage the battery ships in and leaves the buyer to do the multiplication. A portable power station is a sealed, fixed system — internal pack voltage, inverter, and charge controller are all built in and never change — so there’s nothing to multiply and no reason to make a buyer do it. We follow the same convention: the power station finder and every listing on this site quotes Wh directly. The how to size a power station guide walks through matching that Wh figure to your appliances; a unit like the BLUETTI AC180 Portable Power Station is listed at 1,152 Wh and $449, not as an Ah-and-volts pair, and a smaller one like the Jackery Portable Power Station Explorer 1000 v2 at 1,070 Wh for $519 works the same way. For a wider spread of current prices per watt-hour across the power stations we track, see the power station price index.
Converting a phone or laptop battery’s mAh
Phone and laptop specs are almost always given in milliamp-hours (mAh), which is just Ah × 1000. Convert to Ah first, then multiply by the cell’s nominal voltage, which for a standard lithium-ion phone cell is 3.85V. A 3,500mAh phone battery is 3.5Ah, and 3.5 × 3.85 = 13.5Wh. Laptop batteries are different, because they run several cells in series at a higher nominal voltage: a typical laptop pack is about 3,000–8,000mAh at 11.1–15.4V, or roughly 40–99.9Wh. For example, a 6,000mAh pack at 11.55V is 6 × 11.55 = 69Wh. Check the pack voltage on the label rather than assuming 3.85V. The pattern is identical to the battery examples above: divide the mAh figure by 1,000 to get Ah, then multiply by nominal voltage. For the chemistry behind why lithium-ion and LiFePO4 cells use different nominal voltages and different usable capacity, see LiFePO4 vs lithium-ion.
The airline 100Wh carry-on limit
This is where the Ah-to-Wh conversion has a real, practical consequence. The FAA and most airlines cap spare lithium battery packs carried onto a plane at 100Wh with no approval needed; batteries between 101Wh and 160Wh need airline approval and are limited to two spares per passenger; anything above 160Wh isn’t allowed as carry-on at all. Most portable power stations and USB power banks print their Wh rating directly on the label or in the specs, so you often don’t need to calculate anything. But if a device only lists Ah and V — common on generic power banks and some jump-starter packs — do the math before you pack it. A 20,000mAh (20Ah) phone power bank at 3.7V nominal is 20 × 3.7 = 74Wh, comfortably under the no-approval limit. A 27Ah automotive jump-starter battery at 12V nominal is 27 × 12 = 324Wh — more than double the absolute ceiling, and not permitted as carry-on or checked baggage. When you’re shopping for a power station you intend to fly with, filter by Wh on the power station finder rather than by Ah, and check it against the 100Wh line before you buy.
Do the arithmetic before you buy
The rule holds everywhere on this site and everywhere you’ll encounter Ah and Wh figures: Wh = Ah × V, and an Ah number by itself is not a capacity, it’s half of one. Once you have a Wh figure, you can size it against real loads using the appliance wattage chart, which lists running watts for the appliances people most often plan a power station or battery bank around. Do that multiplication once, write the voltage down next to the Ah figure, and every battery comparison after that becomes straightforward.