OctaBattery Capacity Converter — mAh to Wh
Convert battery capacity between milliamp-hours (mAh) and watt-hours (Wh). Enter any two values and the third calculates instantly.
For educational and reference use only. Always verify results before use in real-world designs or safety-critical applications. For more information, see Calculation Assumptions and Disclaimer.
How to Use This Battery Capacity Converter
Fill in any two of the three fields — capacity (mAh), voltage (V), or energy (Wh) — and the third calculates automatically. Common battery voltages: 1.5V (AA/AAA), 3.7V (Li-ion cell), 3.2V (LiFePO4), 7.4V (2S Li-ion pack), 11.1V (3S Li-ion pack), 12V (lead acid).
Battery Capacity Formula
mAh = milliamp-hours (charge capacity), V = nominal voltage, Wh = watt-hours (energy capacity).
Example
Wh = (4000 × 3.7) / 1000 = 14.8 Wh
Laptop battery: 56 Wh at 11.4V
mAh = (56 × 1000) / 11.4 = 4912 mAh
Frequently Asked Questions
Why do batteries show both mAh and Wh?
mAh tells you the charge capacity — how many milliamps can flow for how many hours. Wh tells you the energy
content — the ability to do actual work. Wh is more useful for comparing batteries of different voltages, which
is why EU regulations require Wh labelling on devices.
What is the nominal voltage to use for Li-ion cells?
Use 3.7V for standard Li-ion and Li-polymer cells. For LiFePO4 (lithium iron phosphate), use 3.2V. These are
average discharge voltages — actual voltage varies from 4.2V (full) to 2.5–3.0V (empty).
Can I compare the capacity of different battery types using Wh?
Yes — Wh is the most accurate way to compare energy across different chemistries and voltages. A 9V 500 mAh
battery (4.5 Wh) stores the same energy as a 3.7V 1216 mAh Li-ion cell (approximately).
Why does the calculator also show Joules?
Joules is the SI unit of energy. 1 Wh = 3600 J. This is useful in physics and engineering contexts where energy
must be expressed in SI units.