Amp Hours to Watt Hours Calculator

Why Ah alone doesn't tell you battery capacity

Amp-hours (Ah) measure electric charge — how much current a battery can deliver over time. They do not measure energy. Two batteries can share the same Ah rating and store completely different amounts of usable energy, because energy also depends on voltage.

Watt-hours (Wh) measure energy directly, so they're the number to use when comparing batteries that run at different voltages. The formula is simple: watt-hours = amp-hours × volts. That's it — no other inputs, no adjustments.

Worked example: a 100Ah 12V battery stores 100 × 12 = 1,200 Wh. A 50Ah 24V battery stores 50 × 24 = 1,200 Wh too. Both batteries hold the exact same amount of energy, even though one has double the Ah rating of the other. If you only compared the Ah numbers, you'd wrongly assume the 100Ah battery held twice the capacity.

Common battery voltages worth knowing

12V is the standard for most RV, marine, and portable power station batteries — it's the voltage you'll see on the label of a typical deep-cycle battery or a Jackery/EcoFlow-style unit. 24V shows up in larger RV and marine battery banks, and in some higher-capacity portable power stations. 48V is common in whole-home battery systems and off-grid solar inverters, because higher voltage moves the same power with less current (and thinner, cheaper wiring). Some whole-home battery products, like Tesla Powerwall, run their internal battery pack at voltages well above 48V — the published spec sheet lists usable kWh, not a pack Ah rating, for exactly this reason: energy is what matters, not charge.

Common mistakes when comparing batteries

The most common mistake is comparing two products' Ah ratings directly without checking whether they run at the same voltage. A 200Ah 12V battery stores 2,400 Wh. A 100Ah 24V battery stores the same 2,400 Wh, despite having half the Ah rating. A 100Ah 48V battery stores 4,800 Wh — double either of those — despite sharing the exact same 100Ah rating as the 24V example. Always convert to Wh before you decide which battery gives you more runtime for your appliances.

A second mistake is assuming "usable" and "rated" capacity are the same. Many lithium batteries publish a usable Wh figure that already accounts for depth of discharge, while older lead-acid Ah ratings sometimes assume a full discharge you shouldn't actually use. Check the product's published spec sheet for a usable capacity figure before you convert.