Mobile & Electronics

Ah to Wh Calculator

Amp-hours into watt-hours - the conversion for inverter, UPS and vehicle batteries, where Ah is the usual label.

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Your figures

The Ah figure on the battery. Inverter and vehicle batteries are labelled this way.

The battery's nominal voltage - 12 V is usual for a single inverter or car battery, 24 V or 48 V for banks wired in series.

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Result

Your result

Enter your figures and the result appears here.

Estimates only. Rates, fees and specifications change. Confirm against the official source before you rely on a figure — see our disclaimer.

About this calculator

Amp-hours tell you how much charge a battery holds; watt-hours tell you how much energy it holds. A 100 Ah battery at 12 V stores 1,200 Wh. The identical 100 Ah at 48 V stores 4,800 Wh — four times as much, from the same headline number.

This matters when comparing inverter batteries or sizing a system, because a supplier quoting Ah has told you only half of what you need to know.

How to use this calculator

  1. Enter the capacity in Ah, or in mAh for a smaller pack.
  2. Enter the nominal voltage — 12 V for a single inverter or car battery, 24 V or 48 V for a series bank.
  3. Read the watt-hours. That is what you compare against another battery and what you divide by a load to get a runtime.

The formula

Wh = Ah x V

For a bank of batteries wired in series, the voltages add and the Ah stays the same: four 12 V 100 Ah batteries in series are a 48 V 100 Ah bank holding 4,800 Wh. Wired in parallel, the voltage stays and the Ah adds: the same four give 12 V 400 Ah, which is the same 4,800 Wh by a different route.

SymbolMeaningUnit
Ah Charge the battery holds Ah
V Nominal voltage V
Wh Energy the battery holds Wh

Worked example

A 100 Ah inverter battery at 12 V:

Wh = 100 x 12 = 1,200 Wh = 1.2 kWh

A 48 V bank of the same capacity:

Wh = 100 x 48 = 4,800 Wh = 4.8 kWh

Notes and limits

  • Compare batteries on watt-hours. Ah alone is only comparable between batteries at the same voltage.
  • This is nominal energy. A lead-acid battery should not be run flat — taking one below about half its capacity repeatedly shortens its life sharply — so usable energy is considerably less than this figure.
  • Lead-acid capacity is also rated at a particular discharge rate, usually over 20 hours. Drawing harder than that yields less than the rating, sometimes much less.
  • Series wiring adds voltage; parallel wiring adds amp-hours. Either way the watt-hours are the same.
  • For backup time from this energy, use the inverter backup calculator.

What this calculation assumes

  • The voltage entered is the battery's nominal voltage.
  • This is nominal energy; usable energy is lower, particularly for lead-acid.
  • The rated capacity assumes the manufacturer's discharge rate, usually over 20 hours.

Frequently asked questions

How do I convert Ah to Wh?

Multiply the amp-hours by the battery voltage. A 100 Ah battery at 12 V is 1,200 Wh.

How many watt-hours is a 150 Ah inverter battery?

At 12 V, 1,800 Wh. But usable energy is well below that: lead-acid batteries should not be discharged much past half, so plan on roughly 900 Wh of practical capacity.

Does wiring batteries in series or parallel change the energy?

No. Series adds voltage and keeps the amp-hours; parallel adds amp-hours and keeps the voltage. Either way the watt-hours are the same, which is another reason Wh is the figure to think in.

Why does my battery deliver less than its rating?

Lead-acid capacity is rated at a slow discharge, typically over 20 hours. Drawing harder gives less - sometimes substantially less. Age, temperature and depth of discharge all reduce it further.

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