Free solar and battery calculators

Amp Hour Calculator (Ah to Wh)

Convert amp hours to watt-hours and back, find the Ah a load uses, or add up a series and parallel battery bank.

The amp hour calculator converts between amp-hours (Ah) and watt-hours (Wh), works out the amp-hours a load uses over a set time, and totals a battery bank wired in series and parallel. It runs in your browser, is free, and needs no sign-up. Enter a battery’s capacity or energy, its voltage, and any load or wiring details, then read the result rows.

Use it when you are sizing a battery, comparing batteries that have different voltages, or checking how much charge a device will draw over a given number of hours. Because amp-hours alone can mislead when voltages differ, the tool also shows watt-hours, which compare batteries fairly.

Amp hour calculator example

How to use the Amp hour calculator

  1. Open the “What do you want to find?” drop-down and choose a mode: Watt-hours from amp-hours (Ah → Wh), Amp-hours from watt-hours (Wh → Ah), Amp-hours used by a load (current × hours), or Battery bank in series and parallel.
  2. Enter the “Battery voltage (V)” as the nominal voltage printed on the battery, such as 12 V, 24 V or 48 V.
  3. For Ah → Wh, type your value in “Battery capacity (Ah)”. Milliamp-hours (mAh) also work.
  4. For Wh → Ah, type your value in “Energy (Wh)”. Kilowatt-hours (kWh) are also accepted.
  5. For a load, set “Load is given as” to Current in amps (A) or Power in watts (W). Then fill in “Load current (A)” or “Load power (W)”, and enter “Time (h)”.
  6. For a battery bank, enter “Batteries in series” and “Strings in parallel” as whole numbers, plus the capacity of one battery.
  7. Read the result rows. Then open “How it was calculated” to check each step against your own numbers.

The example buttons above the form (100 Ah, 12 V, 200 Ah, 48 V, 4 × 12 V 100 Ah, 2s2p and 5 A for 8 h) fill the form with a sample you can change. Copy result copies the result lines and a link. Copy link saves every input in the page address, so the same calculation reopens later. Print / save as PDF produces a copy with inputs, results, steps and the date. Reset restores the starting example.

How do you calculate amp hours?

Amp-hours used equal current multiplied by time: amp-hours = current (A) × hours. A 5 A load running for 8 hours uses 40 Ah. To turn amp-hours into watt-hours, multiply by voltage: watt-hours = amp-hours × voltage. So 100 Ah at 12 V gives 1,200 Wh. To go the other way, divide: amp-hours = watt-hours ÷ voltage.

If a load is rated in watts, convert it to amps first by dividing watts by battery voltage: current = watts ÷ voltage. A 60 W load on a 12 V battery draws 5 A, so running for 10 hours uses 50 Ah.

What is the difference between amps and amp hours?

Amps measure current, which is how fast charge flows at a moment. Amp-hours measure charge, which is the total amount of flow over time. Because they measure different things, you cannot convert Ah to A without knowing the time.

Amp-hours also cannot compare batteries at different voltages on their own. A 100 Ah battery at 12 V stores 1,200 Wh, while a 100 Ah battery at 24 V stores 2,400 Wh. The 24 V battery holds twice the energy even though the amp-hour rating is the same, so watt-hours are the fair comparison.

Ah to Wh conversion and back

The Ah to Wh conversion (amp hour to watt hour conversion) is the most useful one, because watt-hours compare batteries of any voltage: ampere hour to watt hour is Ah × V, so a 50 Ah 24 V battery holds 1,200 Wh, the same as a 100 Ah 12 V battery. Going from watt hour to ampere hour divides by the voltage: 2,400 Wh at 48 V is 50 Ah. An Ah to watt conversion is not possible without time, since watts are a rate; an Ah to watt hour conversion is what most people mean. Likewise, ampere hour to ampere needs the hours: 100 Ah delivered over 20 hours is 5 A.

Worked examples

InputResult
100 Ah, 12 V1,200 Wh
9.6 kWh, 48 V200 Ah
5 A, 8 h40 Ah
60 W, 12 V, 10 h50 Ah
2 × 2, 12 V, 100 Ah24 V, 200 Ah, 4,800 Wh

Calculated by the tool above with these values.

Frequently asked questions

How do you convert Ah to Wh?

Multiply the amp-hours by the battery voltage. For example, 100 Ah at 12 V is 100 × 12 = 1,200 Wh. In the Ah → Wh mode, this shows in the Energy (Wh) row.

How many watts is 100 Ah?

100 Ah cannot be turned into watts on its own, because amp-hours measure charge and watts measure power. At 12 V, 100 Ah stores 1,200 Wh, which is enough for 100 W for 12 hours, or 1,200 W for one hour, ignoring losses.

How do series and parallel batteries add up?

Series connections add the voltages and keep the amp-hours the same. Parallel connections add the amp-hours and keep the voltage the same. Watt-hours add either way. Four 12 V 100 Ah batteries wired 2 in series and 2 in parallel give 24 V 200 Ah, or 4,800 Wh.

Can I enter mAh instead of Ah?

Yes. The battery capacity box accepts milliamp-hours (mAh) as well as Ah. One amp-hour equals 1,000 mAh.

Does the calculator upload my numbers?

No. Everything runs in your browser and nothing is uploaded. There is no sign-up, and the tool is free.

Can I use the results in a quote or report?

Yes. Results, charts and printouts can be used freely in commercial work such as quotes, proposals, reports and service records, with no attribution needed.

Sources