kWh to Ah Calculator

A 1.2 kWh battery holds 100Ah at 12V, 50Ah at 24V and 25Ah at 48V. Converting kWh to Ah means dividing the watt hours by the pack’s nominal voltage, which is why one battery carries three different amp hour labels and why an Ah figure without a voltage is not an answer.

The kWh to Ah formula, explained

Two operations, in this order. Kilowatt hours times 1,000 gives watt hours; watt hours divided by volts gives amp hours. A 3 kWh bank at 24V is 3,000 ÷ 24 = 125Ah.

Each term is doing a distinct job, and keeping them straight is what prevents the error below:

• Kilowatt hours (kWh) measure energy. It is the unit your electricity bill counts in, the unit a solar array’s daily yield is quoted in, and the unit home storage is sold in.
• The 1,000 is a unit change and nothing more, from kilowatt hours to watt hours. It is not physics, and it is the term people drop, which puts the answer out by three orders of magnitude.
• Volts (V) convert energy back into charge. Use the nominal voltage of the battery or bank — the number on the label, usually 12V, 24V or 48V — not a meter reading, and not the voltage of the outlet an appliance plugs into.

That last clause is the mistake this conversion produces over and over: dividing by 120V because 120V is what comes out of the wall. Amp hours are a DC battery specification and belong to the battery’s own voltage. Divide 2 kWh by 120V and you get 16.7Ah, an arithmetically valid number that describes nothing you can buy. Divide the same 2 kWh by 12V and you get 166.7Ah, which is a figure a battery supplier would recognise and quote against.

Conversion table at 12V, 24V and 48V

These are the three nominal system voltages capacity is actually rated at: 12V for RV, van and marine banks, 24V for mid-size off-grid builds, and 48V for home battery racks and larger solar. Read across and the stored energy is identical in every row — only the label changes. Amp hours halve each time the voltage doubles.

The 12V column becomes an argument against itself once the numbers get large. Energy is constant across a row, but current is not: pulling 3,000W from a 12V bank is 250 amps, and from a 48V bank it is 62.5 amps. That ratio sets cable gauge, fuse rating and busbar size, and decides how much of the budget disappears into copper. It is why home storage settled on 48V and stayed there. If your starting figure is already in watt hours rather than kilowatt hours, watt hours to amp hours skips the first step.

Why this conversion matters for portable power and solar

The two halves of this market quote capacity in different units, and neither side converts for you. Portable power stations are sold in watt hours, because watt hours predict runtime. Loose batteries, RV house banks and rack modules are sold in amp hours, because amp hours predict wiring, charge current and fusing. Nearly every cross-shopping decision in the category runs through this conversion.

Three places it changes what you buy:

• A finished unit against a DIY bank. A 2 kWh power station and a 12V 200Ah battery sound comparable. They are 2 kWh and 2.4 kWh, and you cannot see that until both are in the same unit. Convert before you compare price. Our power station sizing guide works from a load list to a capacity, and the power stations page lists the catalogue that way.
• Sizing an RV or van bank. Work out consumption in kWh per day, convert at 12V, and you have the number every battery supplier prices in. A modest 1.5 kWh day is 125Ah before a single loss is counted, already more than one 100Ah battery delivers. That is the arithmetic that sells people a bank one battery too small. The off-grid and RV section covers the rest of the build.
• Matching storage to a solar array. Panel output and daily yield are quoted in watt hours; the bank is quoted in amp hours. Carrying one cloudy day for a 5 kWh household is roughly 104Ah at 48V on paper, and meaningfully more once depth of discharge is allowed for. The solar sizing guide handles the panel side, and the solar battery calculator returns a bank size in both units at once.

Which voltage to divide by

Use the nominal voltage, never the voltage on your meter. A 12V lead-acid battery rests near 12.7V when full and reads above 14V while charging. Divide by the charging voltage and the amp hour answer comes out roughly 15% small, which quietly undersizes the bank you then go and buy.

Every voltage you are likely to meet, with 1 kWh and 5 kWh converted at each:

Two rows deserve a second look. LiFePO4 packs marketed as “12V” and “48V” are really 12.8V and 51.2V, built from 3.2V cells in series, so the honest amp hour figure sits about 6% below what the round-number division gives. Notice that 5 kWh at 51.2V works out at 97.7Ah, which is precisely why 100Ah is the standard home storage rack module.

The 120V row is there to be dismissed, and it is the AC-versus-DC distinction in a single line. No battery in this category runs at 120V nominal. 120V is what the inverter produces on the far side of the conversion, after the battery has already done its work in DC. If you are sizing storage for AC appliances, divide at the battery voltage and then add for inverter losses, which is the next section.

Where a manufacturer publishes both a watt hour rating and an amp hour rating for the same product, trust the watt hour rating and do not convert at all. It already reflects the exact cell arrangement inside that pack. Convert only when one of the two is missing, which on loose batteries is most of the time.

From the nameplate number to the battery you buy

The figure the formula returns is nameplate capacity. It is not what reaches an appliance, and two separate losses stack in between.

Depth of discharge comes first. Lead-acid and AGM shed cycle life quickly below half charge, so the working convention is 50% usable. LiFePO4 tolerates deep cycling and is generally rated at 90% or better. Inverter loss comes second and applies only to AC loads: converting DC to 120V AC costs roughly 10%, and proportionally more at very small loads. A DC appliance wired straight to the bank skips that stage entirely, which is the real reason 12V fridges and fans earn their place in a van.

Working backwards from a daily AC total, at 12V, through an inverter at 90%:

The gap between the third column and the fourth is the entire argument for lithium in a storage application, and it is wider than the price difference suggests. A refrigerator alone runs 1–2 kWh a day, which the refrigerator wattage guide breaks down properly, so a single 12V 100Ah AGM battery will not carry a fridge overnight and back — whatever the nameplate arithmetic implies. At 24V, halve every figure in the table.

Frequently asked questions