Ah to kWh Calculator

A 100Ah battery holds 1.2 kWh at 12V, 2.4 kWh at 24V and 4.8 kWh at 48V. Converting Ah to kWh needs the pack voltage, because amp hours measure charge rather than energy: the same 100Ah label can describe four times the stored energy depending on the system it belongs to.

The Ah to kWh formula, explained

Amp hours times volts gives watt hours, and watt hours divided by 1,000 gives kilowatt hours. A 280Ah rack module at 51.2V nominal is 280 × 51.2 = 14,336 watt hours, which is 14.34 kWh.

Three terms, each doing a different job:

• Amp hours (Ah) measure charge, not energy. 100Ah is nominally 100 amps for one hour, or 5 amps for 20 hours. On its own the number is only half a specification.
• Volts (V) are what turn charge into energy. Use the nominal voltage of the cell, battery or bank — the figure on the label — not what a meter reads at the terminals.
• The 1,000 is a unit change and nothing more. Electricity bills, solar yields and home battery quotes are all denominated in kWh, which is why this conversion comes up so often.

The mistake that costs people money is comparing amp hours across different voltages. Two batteries advertised as 100Ah and 200Ah look like an obvious ranking until you notice the first is a 48V rack module and the second is a 12V RV battery: 4.8 kWh against 2.4 kWh, so the smaller-sounding battery stores twice the energy. Amp hours size cable and fuses. They do not compare products.

Conversion table at 12V, 24V and 48V

The columns assume nominal system voltages, which is how capacity is rated: 12V is the RV, van and marine standard, 24V suits mid-size off-grid builds, and 48V is what home battery racks and larger solar systems run. The 100Ah row is the reference line most specifications are quoted against.

Doubling the voltage doubles the energy, so every 24V figure is twice the 12V figure and every 48V figure is twice that again. Amp hours to watt hours is the same sum without the final division, and kWh to Ah reverses it.

Why it matters for power stations 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 solar storage modules are sold in amp hours, because amp hours predict wiring, charge current and fusing. Put a 2 kWh power station next to a 12V 100Ah battery and you are really comparing 2 kWh against 1.2 kWh.

Three places the conversion decides a purchase:

• Sizing storage against a daily load. Work out consumption in kWh per day first, then convert to amp hours at your system voltage. A modern refrigerator alone runs roughly 1–2 kWh per day, which our refrigerator wattage guide breaks down properly. That is already more than a single 12V 100Ah battery delivers once losses are counted.
• Matching a solar array to a bank. Panel ratings and daily yield are quoted in watt hours, so a bank quoted in amp hours cannot be checked against them until you convert. Storing 5 kWh of usable AC energy takes roughly 130Ah at 48V once depth of discharge and inverter losses are allowed for, and about 515Ah at 12V. That gap is the whole reason larger systems move to 48V. The solar sizing guide covers the panel side.
• Choosing between a DIY bank and a finished unit. Converting both to kWh is the only fair comparison. Once you have the number, compare power stations by capacity, or narrow the catalogue with the power station finder.

Nameplate kWh against the kWh you can spend

The figure the formula gives you is the battery’s full theoretical energy content. You will never see all of it at an outlet, for two reasons that stack.

Depth of discharge comes first. Lead-acid and AGM lose cycle life badly below roughly 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 it applies only to AC loads: converting DC to 120V AC costs about 10%, and more at very small loads. Run a DC appliance — a 12V compressor fridge, LED lighting — straight from the bank and that stage disappears entirely, which is worth 10% of your capacity for free.

The table below assumes LiFePO4 at 90% depth of discharge and an inverter at 90% efficiency.

On a lead-acid or AGM bank held to 50% depth of discharge, halve the DC column and then apply the inverter loss: a 12V 200Ah AGM bank rated 2.4 kWh delivers about 1.08 kWh to AC appliances. That difference, rather than the price per amp hour, is the real argument for lithium in a storage application.

Which voltage to multiply by

Use the nominal voltage, never the voltage you measure. A 12V lead-acid battery rests at about 12.7V when full and can read 14.4V while charging. Multiply by 14.4 instead of 12 and your answer is 20% too high, which is exactly the kind of optimism that ruins a sizing calculation.

The same 100Ah, at every nominal voltage you are likely to meet:

The LiFePO4 rows catch people out. Packs sold as 12V, 24V and 48V are built from 3.2V cells and are really 12.8V, 25.6V and 51.2V, so the honest energy figure is about 6% higher than the round-number multiplication.

Small packs work the same way at a different scale. A 3.7V cell rated 5,000mAh is 5Ah × 3.7V = 18.5Wh, or 0.0185 kWh — for power banks and phone cells, mAh to Wh keeps the decimal point in the right place. An e-bike pack marked 48V 20Ah is 0.96 kWh.

Where a manufacturer publishes both an amp hour and a watt hour rating, trust the watt hour rating and skip the conversion: it already reflects the exact cell arrangement in that product. Convert only when the watt hour figure is missing, which on loose batteries is most of the time. For a whole system rather than one battery, the solar battery calculator returns a bank size in both units.

Frequently asked questions