Watt-hours and amp-hours measure different things: Wh measures total energy, Ah measures charge capacity at a given voltage. Converting between them is simple division, but getting the voltage wrong gives you a wildly incorrect answer. This calculator handles the math cleanly.
How to Convert Wh to Ah (Step by Step)
- Identify the watt-hour rating. Find the Wh value on the battery label, product spec sheet, or manufacturer website. Power banks, laptop batteries, and some solar batteries list Wh prominently. If only mWh is listed, divide by 1,000 to get Wh.
- Identify the nominal voltage. Common voltages: 3.7V (lithium-ion cells and power banks), 12V (car and marine batteries), 12.8V (LiFePO4 "12V"), 24V (larger systems), 48V (off-grid solar). Using the wrong voltage gives the wrong amp-hour number.
- Divide. Amp-hours = Watt-hours / Voltage. A 1,000Wh battery at 12V = 83.3Ah. That same 1,000Wh at 48V = only 20.8Ah — but it stores the same energy.
- Verify units. If your source lists kWh (kilowatt-hours), multiply by 1,000 to get Wh first. A 5kWh home battery = 5,000Wh.
Wh to Ah Quick Reference Table
| Wh | At 3.7V (Ah) | At 12V (Ah) | At 24V (Ah) | At 48V (Ah) |
|---|---|---|---|---|
| 37 Wh | 10 Ah | 3.1 Ah | 1.5 Ah | 0.8 Ah |
| 74 Wh | 20 Ah | 6.2 Ah | 3.1 Ah | 1.5 Ah |
| 500 Wh | 135 Ah | 41.7 Ah | 20.8 Ah | 10.4 Ah |
| 1,000 Wh | 270 Ah | 83.3 Ah | 41.7 Ah | 20.8 Ah |
| 2,400 Wh | 649 Ah | 200 Ah | 100 Ah | 50 Ah |
| 5,000 Wh | 1,351 Ah | 416.7 Ah | 208.3 Ah | 104.2 Ah |
Remember: higher voltage systems use fewer amp-hours for the same stored energy. This means thinner cables, smaller fuses, and lower current — one of the main reasons large off-grid systems run at 48V instead of 12V.
Frequently Asked Questions
Sizing a solar battery bank? The <a href="/solar/solar-battery-bank-size-calculator">solar battery bank size calculator</a> uses Wh to match storage to daily generation.
Wh to Ah conversion is the most fundamental battery math skill. Whenever you see a battery rated in one unit and need the other, divide by voltage. Get comfortable with this conversion and every other battery calculation becomes straightforward.
Last updated:
Written and maintained by Dan Dadovic, Developer & Off-Grid Energy Enthusiast. On the energy side, Dan has hands-on experience with residential solar panel installation, DIY battery bank construction, off-grid power systems, and wind power — all from building and maintaining his own systems..
Disclaimer: Calculator results are estimates based on theoretical formulas. Actual performance varies with temperature, battery age, load patterns, and equipment condition. For critical electrical work, consult a licensed electrician.