Electrical units and conversion

Watt-hours to amp-hours converter

Divide watt-hours by the pack's nominal voltage. The answer is only meaningful if you state the voltage alongside it, because amp-hours measure charge, not energy.

How do you convert watt-hours to amp-hours?

Amp-hours = watt-hours ÷ nominal voltage. A 1,200 Wh battery is 100 Ah at 12 V, 50 Ah at 24 V and only 23.44 Ah at 51.2 V — the same stored energy, three different amp-hour numbers. That is the whole reason the conversion needs a voltage: watt-hours are energy and can be compared directly, while an amp-hour figure without its voltage cannot be compared with anything. The arithmetic is exact and reverses exactly; nothing here accounts for how much of that capacity you can actually use.

Your inputs

Energy in watt-hours

Nominal voltage

Use the nominal voltage on the label, not the fully charged or resting voltage. The conversion is only as meaningful as this number.

Common voltages

100.00 Ah

at 12.0 V nominal

1,200.0 Wh ÷ 12.0 V. Amp-hours measure charge, so this figure only has meaning alongside the voltage it was calculated at.

Exact given your inputs

Watt-hours: 1,200.0 Wh
Amp-hours: 100.00 Ah
Nominal voltage: 12.0 V
Kilowatt-hours: 1.200 kWh

Round-trip check

Converting the displayed result straight back gives 1,200.000 Wh against an exact 1,200.000 Wh. The pair is exact in both directions at this voltage.

Method

Ah = Wh ÷ V
Ah = 1,200.0 ÷ 12.0 = 100.0000 Ah

This converter changes units. It does not tell you how much energy you can actually take out of the battery.

Assumptions

The voltage you entered is treated as the pack's nominal voltage across the whole discharge.
The conversion is pure arithmetic: no depth of discharge, inverter efficiency, temperature or discharge-rate effect is applied.
Displayed values are rounded; the arithmetic above is carried at full precision.

What can change the result?

Actual terminal voltage, which falls through the discharge and rises while charging
Chemistry: a lead-acid amp-hour rating is quoted at a slow discharge rate and shrinks at high current
Whether the label figure is nominal capacity or usable capacity

The same 1,200 Wh at every common voltage

Vendor converters usually fix 12 V and hide it. The table below holds the energy constant and varies only the voltage, which is the single input that changes the answer.

1,200 Wh converted at each nominal voltage. Exact arithmetic; amp-hours shown to two decimals.
Nominal voltage	Amp-hours	Watt-hours	Kilowatt-hours
3.7 V	324.32 Ah	1,200 Wh	1.200 kWh
12 V	100.00 Ah	1,200 Wh	1.200 kWh
24 V	50.00 Ah	1,200 Wh	1.200 kWh
48 V	25.00 Ah	1,200 Wh	1.200 kWh
51.2 V	23.44 Ah	1,200 Wh	1.200 kWh

Ratings taken from real labels

Each row is converted at the voltage that particular product is rated at, not at a single assumed 12 V.
What it is	Watt-hours	Nominal voltage	Amp-hours
Portable power station, 12 V internal pack	1,002 Wh	12 V	83.50 Ah
100 Ah 12 V leisure battery	1,200 Wh	12 V	100.00 Ah
100 Ah 24 V pack	2,400 Wh	24 V	100.00 Ah
100 Ah 51.2 V LFP rack module	5,120 Wh	51.2 V	100.00 Ah
Laptop cell string quoted at cell voltage	96 Wh	3.7 V	25.95 Ah

What the converted number does not tell you

An amp-hour rating is quoted at a particular discharge rate. Lead-acid capacity is normally stated at a 20-hour rate, and drawing the same battery down in two hours yields substantially fewer amp-hours than the label — the well-known Peukert effect. Lithium iron phosphate is far less sensitive to rate, but its label figure is still nominal capacity, not what an inverter will hand you at an AC outlet.

The second thing to watch is which voltage the manufacturer used. A 51.2 V LFP module is often marketed as a “48 V” battery. Convert 5,120 Wh at 48 V and you get 106.67 Ah instead of the true 100.00 Ah — a 6.7% error introduced purely by the voltage label.