Formula
mAh = Wh × 1000 ÷ V
Worked example
A 57 Wh laptop battery with an 11.4 V pack: mAh = 57 × 1000 ÷ 11.4 = 5,000 mAh.
Reference table
Quick reference
| Wh | mAh @ 3.7 V | mAh @ 5 V |
|---|---|---|
| 5 | 1,351.35 | 1,000 |
| 10 | 2,702.7 | 2,000 |
| 20 | 5,405.41 | 4,000 |
| 37 | 10,000 | 7,400 |
| 50 | 13,513.51 | 10,000 |
| 100 | 27,027.03 | 20,000 |
Where this shows up in the real world
Laptop batteries, e-bike packs and drone batteries are specced in Wh; the replacement-cell market and many spec sheets still speak mAh. Converting needs the pack voltage — a 57 Wh laptop battery at 11.4 V is 5,000 mAh — and doing it correctly is how you avoid buying a 'compatible' replacement with two-thirds the real capacity.
Common mistakes to avoid
mAh without a voltage is a meaningless number, and comparing mAh across different-voltage packs is the classic spec-sheet con. Convert everything to Wh first, compare, then convert back if you must. Also note nominal pack voltage (3.7, 7.6, 11.4 V…) is what the math uses — not the charger's output voltage printed on the adapter.
Frequently asked questions
Why does the same Wh give different mAh figures?
mAh depends on voltage. 37 Wh is 10,000 mAh at 3.7 V but only 3,243 mAh at 11.4 V — same energy, different bookkeeping.
Which figure should I compare when buying?
Wh is the honest energy figure. Comparing mAh across devices with different voltages is misleading.
Where do I find my battery's voltage?
Printed on the battery label or in the device specs — phone cells ~3.7–3.85 V, laptop packs commonly 7.6 V or 11.4 V.