mAh to mWh Calculator
Convert milliamp-hours to milliwatt-hours to compare phone, wearable and power bank batteries by real energy.
Quick answer
To convert mAh to mWh, multiply the milliamp-hours by the nominal voltage. mWh = mAh × V. A 5,000 mAh phone battery at 3.85 V stores 5,000 × 3.85 = 19,250 mWh, which is 19.25 Wh. The same 5,000 mAh at 3.7 V is 18,500 mWh, so always use the voltage printed on the battery.
How to use the mAh to mWh calculator
- Enter the capacity in mAh. Type the milliamp-hour rating from the battery, device box or spec sheet, such as 300 mAh for a smartwatch, 5,000 mAh for a phone or 10,000 mAh for a power bank.
- Enter the nominal voltage. Use the cell or pack voltage printed beside the mAh figure. Modern phones are usually 3.85 V or 3.87 V, older phones and power banks 3.7 V, NiMH AA cells 1.2 V and two cell packs 7.4 V.
- Read the energy in mWh. The large number is the stored energy in milliwatt-hours. The cards show it in Wh and kWh, and for low voltage cells they show the mAh that the same energy equals at 5 V USB.
mAh to mWh formula
mAh tells you how much charge a battery holds. mWh tells you how much energy that charge carries, which depends on the voltage it is delivered at. Multiply the two and the milli prefixes stay together, so the result is already in milliwatt-hours.
Where:
- mWh is the energy in milliwatt-hours.
- mAh is the rated charge capacity in milliamp-hours.
- V is the nominal voltage of the cell or pack.
- Wh is the same energy in watt-hours. 1 Wh = 1,000 mWh.
If your battery is listed in mWh and you need the charge rating, use the mWh to mAh calculator instead.
Worked examples
Example 1: comparing two phones
Phone A has a 5,000 mAh battery at 3.85 V. Phone B has a 4,900 mAh battery at 3.87 V.
Phone A holds about 1.5% more energy. The 100 mAh gap on the spec sheet is close to the real difference here because the voltages are similar. Against an older 3.7 V phone the mAh comparison would be misleading.
Example 2: smartwatch and earbuds
Small wearables are often rated in mAh only. A watch with a 300 mAh cell at 3.85 V and an earbud case with a 500 mAh cell at 3.7 V:
Both are tiny next to a phone. A 10,000 mAh power bank at 3.7 V holds 37,000 mWh, enough in theory for about 32 watch charges before losses.
Example 3: rechargeable AA batteries
A NiMH AA cell is rated 2,000 mAh at 1.2 V. A lithium-ion 18650 cell is rated 3,000 mAh at 3.6 V.
The 18650 has 1.5 times the mAh but 4.5 times the energy, because its voltage is three times higher.
mAh to mWh conversion table
Values in mWh, calculated as mAh × V.
| Capacity (mAh) | 3.7 V | 3.85 V | 7.4 V | 11.1 V | 14.8 V |
|---|---|---|---|---|---|
| 1,000 | 3,700 | 3,850 | 7,400 | 11,100 | 14,800 |
| 2,000 | 7,400 | 7,700 | 14,800 | 22,200 | 29,600 |
| 3,000 | 11,100 | 11,550 | 22,200 | 33,300 | 44,400 |
| 4,000 | 14,800 | 15,400 | 29,600 | 44,400 | 59,200 |
| 5,000 | 18,500 | 19,250 | 37,000 | 55,500 | 74,000 |
| 10,000 | 37,000 | 38,500 | 74,000 | 111,000 | 148,000 |
| 20,000 | 74,000 | 77,000 | 148,000 | 222,000 | 296,000 |
| 26,800 | 99,160 | 103,180 | 198,320 | 297,480 | 396,640 |
The last row shows why voltage matters for travel. A 26,800 mAh bank is 99,160 mWh at 3.7 V, just under 100 Wh, but 103,180 mWh at 3.85 V, just over it.
What affects the result
Cell chemistry sets the voltage
Standard lithium-ion cobalt cells are rated 3.6 V or 3.7 V. Newer high voltage phone cells run at 3.85 V to 3.89 V, so the same mAh holds about 4% more energy. LiFePO4 is 3.2 V, NiMH 1.2 V and alkaline 1.5 V. Pick the right one or the mWh will be off by that ratio.
Cells in series and in parallel
Wiring cells in series adds their voltage and keeps the mAh. Wiring them in parallel adds the mAh and keeps the voltage. Either way the total mWh is the sum of the cells. A two cell 7.4 V pack rated 5,000 mAh and a parallel 3.7 V pack rated 10,000 mAh both hold 37,000 mWh.
USB output voltage
A power bank boosts its 3.7 V cells to 5 V or more for USB. At 5 V the same energy equals fewer milliamp-hours, which is what the third card shows. Some brands print this “rated capacity” at 5 V alongside the cell rating, and it is always lower.
Losses on the way out
The calculator gives stored energy. Boost converters, cables and the charging circuit in your phone each waste some of it, so only part of the mWh reaches the battery you are charging. For energy totals in watt-hours, the mAh to Wh calculator also checks airline limits.
Frequently asked questions
How many mWh is 5,000 mAh?
At 3.85 V, 5,000 mAh is 19,250 mWh. At 3.7 V it is 18,500 mWh and at 3.6 V it is 18,000 mWh. For a two cell 7.4 V pack it doubles to 37,000 mWh. The voltage always changes the answer, so read it from the battery label rather than assuming a value.
Why do some batteries list mWh instead of mAh?
mWh describes energy, which is what actually powers a device and what airlines and regulators care about. Laptops and many EU labels show Wh or mWh because packs of different voltages can then be compared directly. mAh is still common on phones and power banks because it produces a larger, familiar number.
Can I convert mAh to mWh without the voltage?
No. mAh is charge and mWh is energy, and the voltage links them. If the label shows no voltage, 3.7 V is a reasonable guess for a single lithium-ion cell and 3.85 V for a recent phone, but treat the result as an estimate within about 5%.
Is mWh the same as mAh?
No. They only match numerically at exactly 1 V, which almost no battery uses. A 3.7 V cell has 3.7 times as many mWh as mAh. Mixing them up is the most common error when comparing power banks with laptop batteries or reading Windows battery reports.
How many phone charges is a 20,000 mAh power bank?
A 20,000 mAh bank at 3.7 V holds 74,000 mWh. A 5,000 mAh phone at 3.85 V holds 19,250 mWh. Dividing gives 3.8, but after losses of roughly 30% for boosting and charging, expect about 2.5 to 3 full charges in practice.