SunReckon → Watt-Hour to Amp-Hour Calculator
Watt-Hour to Amp-Hour Calculator
Convert between amp-hours and watt-hours for any battery. Enter the amp-hours and voltage to get watt-hours and kWh — or read it backwards to turn watt-hours into amp-hours.
Solar & off-grid explainer
Run the numbers first, then read the why. Start with the calculator below — the example values are pre-filled so you can see how it behaves — then keep scrolling for the method, a worked example, and the questions that trip people up. Everything runs in your browser; nothing you type is stored.
Calculator
Key takeaways
- Watt-hours = amp-hours × voltage (Wh = Ah × V).
- To go the other way, amp-hours = watt-hours ÷ voltage (Ah = Wh ÷ V).
- Divide watt-hours by 1,000 for kilowatt-hours — 1,200 Wh = 1.2 kWh.
- A 100 Ah, 12 V battery holds 1,200 Wh; the same energy is only 50 Ah at 24 V.
How to convert watt-hours and amp-hours
Amp-hours tell you how much charge a battery holds, but they hide the energy unless you know the voltage. Watt-hours fold both together, so they are the honest way to compare batteries. The whole conversion rests on a single definitional identity between power, current, and voltage.
Because energy is fixed but amp-hours depend on voltage, the same 1,200 Wh battery is 100 Ah at 12 V, 50 Ah at 24 V, or 25 Ah at 48 V. That is why two batteries with identical amp-hour labels can store wildly different amounts of energy.
Worked example: 100 Ah at 12 V
Start with a 100 Ah battery at 12 V. Watt-hours = 100 × 12 = 1,200 Wh, which is 1,200 ÷ 1,000 = 1.2 kWh. Reading it backwards, 1,200 Wh ÷ 12 V returns the original 100 Ah. Move that same energy to a 24 V bus and it becomes 1,200 ÷ 24 = 50 Ah — half the amp-hours for identical storage.
Watt-hours for common batteries at 12 V
| Amp-hours (12 V) | Watt-hours | Kilowatt-hours |
|---|---|---|
| 50 Ah | 600 Wh | 0.6 kWh |
| 100 Ah | 1,200 Wh | 1.2 kWh |
| 200 Ah | 2,400 Wh | 2.4 kWh |
| 300 Ah | 3,600 Wh | 3.6 kWh |
From energy to a real bank
Watt-hours are the starting point, not the finish line. Once you know the energy a battery stores, size the whole bank with the battery bank sizing calculator, then check how long it lasts under load with the battery backup runtime calculator. Remember to apply depth of discharge: rated watt-hours assume a full empty, but lead-acid only gives ~50% and LiFePO₄ 80–100%.
Frequently asked questions
How do I convert amp-hours to watt-hours?
Multiply amp-hours by voltage: Wh = Ah × V. A 100 Ah battery at 12 V holds 100 × 12 = 1,200 Wh (1.2 kWh).
How do I convert watt-hours to amp-hours?
Divide watt-hours by voltage: Ah = Wh ÷ V. So 1,200 Wh at 12 V is 100 Ah, but only 50 Ah at 24 V.
What is a watt-hour?
A watt-hour is one watt delivered for one hour — a unit of energy. It measures total stored energy regardless of voltage. 1,000 Wh = 1 kWh.
Why does voltage matter in the conversion?
Amp-hours alone hide the energy. A 100 Ah pack at 48 V holds 4,800 Wh — four times a 100 Ah pack at 12 V (1,200 Wh).
How many watt-hours are in a 100Ah 12V battery?
100 × 12 = 1,200 Wh, or 1.2 kWh. At 50% DoD that's ~600 usable Wh for lead-acid; LiFePO₄ gives ~960–1,200 Wh.
What's the difference between rated and usable watt-hours?
Usable Wh = rated Wh × depth of discharge. Lead-acid ~50%, LiFePO₄ 80–100%, so a 1,200 Wh battery gives 600–1,200 usable Wh.
The Wh = Ah × V relationship is a definitional electrical identity — see the watt-hour definition. All conversions here are exact arithmetic; usable energy depends on depth of discharge.
Last reviewed June 2026