mAh to Wh Calculator
Convert a battery rating in milliamp-hours (mAh) to watt-hours (Wh), and back, using the battery's nominal voltage. Watt-hours are the honest way to compare cells of different voltages, which raw mAh cannot do.
Method based on Wh = mAh x V / 1000 · reviewed June 2026 · method rev 1.0
Why voltage turns charge into energy
How the conversion works
A milliamp-hour is a unit of charge: how much current a cell can supply for how long. A watt-hour is a unit of energy. Energy is charge times voltage, so to turn a mAh rating into watt-hours you multiply by the nominal voltage and divide by 1000 to get from milli-units to whole units:
Wh = mAh × V ÷ 1000 and mAh = Wh × 1000 ÷ V
So a 5000 mAh lithium cell at a nominal 3.7 V holds 5000 × 3.7 ÷ 1000 = 18.5 Wh. The same 5000 mAh at 3.2 V (LiFePO4) holds only 16 Wh - which is exactly why watt-hours, not milliamp-hours, are the fair way to compare cells of different chemistries.
Nominal voltage by chemistry
The conversion is only as good as the voltage you put in. Use the cell's nominal voltage - the average over a discharge - not the fully charged peak.
| Chemistry | Nominal V (per cell) | Notes |
|---|---|---|
| Li-ion / LiPo | 3.7 V | 4.2 V charged, ~3.0 V empty |
| LiFePO4 | 3.2 V | flatter curve, safer chemistry |
| NiMH / NiCd | 1.2 V | per cell; multiply by cells in series |
| Alkaline | 1.5 V | nominal; sags under load |
| Lead-acid | 2.0 V | 12 V for a six-cell battery |
The power-bank trap
This is the most common mistake. A power bank is almost always rated in mAh at its internal 3.7 V lithium cell, but it outputs 5 V over USB. If you convert a 10,000 mAh power bank using 5 V you get 50 Wh, but the real stored energy is 10,000 × 3.7 ÷ 1000 = 37 Wh. Always convert with the voltage the capacity was specified at, which is the cell voltage unless the label clearly says otherwise. This also matters for air travel, where the 100 Wh carry-on limit is checked against the true cell-voltage figure.
Nominal energy is not usable energy
The watt-hour figure from this formula is the nominal stored energy. What you can actually use is lower: a power bank steps the cell voltage up to 5 V and loses energy as heat doing it, the cell's internal resistance wastes more under load, cold weather reduces deliverable capacity, and your device stops drawing current at its cut-off voltage before the cell is truly empty. Treat the result as the ceiling, not the guarantee.
Where engineers use this
Comparing power banks and packs
Two cells with the same mAh can hold very different energy if their voltages differ. Converting both to Wh is the only fair comparison.
Air travel and shipping limits
Lithium battery carry-on and shipping rules are written in watt-hours (commonly 100 Wh and 160 Wh thresholds), so a mAh rating has to be converted first.
Sizing solar and backup storage
Runtime and storage sizing work in watt-hours, so cell and pack mAh ratings get converted to Wh against their nominal voltage before adding them up.
Frequently asked questions
How do I convert mAh to Wh?
Why do I need the voltage?
Which voltage should I use for a power bank?
What nominal voltage does each chemistry use?
Will I actually get that many watt-hours out?
How this relates to other tools
| Standard / tool | Relationship | What it means |
|---|---|---|
| Capacitor code calculator | commonly used with | Both decode a printed component rating into a usable engineering quantity. |
| AWG to mm converter | related calculator | Battery packs feed the conductors this gauge tool sizes for current. |
Related tools and standards
Sources: Energy (Wh) = charge (Ah) x nominal voltage (V) - a definitional relationship, not a product standard · IATA, lithium battery guidance (defines the Wh rating as Ah x nominal voltage; basis of the 100 Wh and 160 Wh air-travel limits). Verify against the current edition.