Why do I need the voltage?

Milliamp-hours measure charge, not energy. The same charge at a higher voltage stores proportionally more energy, which is why mAh figures are only comparable at equal voltage.

What voltage should I use?

Use 3.7 V for standard lithium-ion and lithium-polymer cells, 3.2 V for LiFePO4, and 1.2 V for NiMH rechargeables.

Why does my power bank deliver less than its rating?

The rating is at cell voltage. Boosting to 5 V USB loses 10–20%, so a 10,000 mAh bank typically delivers around 6,000–6,500 mAh at 5 V.

Can I take a 26,800 mAh power bank on a plane?

26,800 mAh at 3.7 V is 99.2 Wh, just under the 100 Wh threshold — which is exactly why that capacity is so common.

mAh to Wh Converter | Battery Capacity Calculator

Conversion Formula

Wh = (mAh × 3.7 V) ÷ 1,000

Charge alone is not energy. Multiply milliamp-hours by the nominal cell voltage — 3.7 V for standard lithium-ion — and divide by 1,000 to get watt-hours.

This formula uses the nominal cell voltage currently set in the calculator (3.7 V). Change it above and this formula updates with it — the relationship is not a fixed unit pair.

Complete Guide to Milliamp-hours to Watt-hours Conversion

What is a Milliamp-hours?

A milliamp-hour (mAh) measures electric charge: one milliampere flowing for one hour. Phone, tablet and power bank marketing uses it because the numbers look impressive, but it says nothing about energy on its own.

What is a Watt-hours?

A watt-hour (Wh) measures energy. It already includes voltage, which makes it the only fair way to compare batteries of different chemistries and cell configurations — and the basis of aviation safety limits.

How the Conversion Works

Energy equals charge multiplied by voltage. Milliamp-hours become watt-hours by multiplying by the nominal cell voltage and dividing by 1,000 to convert milli-units. This calculator uses 3.7 V, the nominal voltage of a standard lithium-ion cell; substitute 3.2 V for LiFePO4 or 1.2 V for NiMH.

Why This Conversion Matters

Airlines, shipping regulations and honest product comparisons all run on watt-hours. A power bank advertised as 20,000 mAh and a laptop battery advertised as 60 Wh sound unrelated, but converted they are 74 Wh and 60 Wh — nearly the same battery.

Scientific Context

Nominal voltage is an average across the discharge curve. A lithium-ion cell starts near 4.2 V and ends near 3.0 V, and 3.7 V represents the working midpoint. Using the peak voltage instead overstates capacity by roughly 13%.

Step-by-Step Conversion Guide

Follow these steps to convert milliamp-hours to watt-hours manually:

Start with your value in milliamp-hours

Example: You want to convert 3000 mAh

Apply the conversion formula

Use the formula: Wh = (mAh × 3.7 V) ÷ 1,000

Calculate the result

3000 mAh = 11.1 Wh

✓

Verify your answer

Use our calculator above to double-check your manual calculation.

Quick Mental Math Tip

Charge alone is not energy. Multiply milliamp-hours by the nominal cell voltage — 3.7 V for standard lithium-ion — and divide by 1,000 to get watt-hours.

Common Conversions

Calculated at 3.7 V (nominal cell voltage). Change the value in the calculator above and this table recalculates.

Milliamp-hours to Watt-hours conversion table at 3.7 V
Milliamp-hours (mAh)	Watt-hours (Wh)	Watt-hours → Milliamp-hours
1000	3.7	1000 Wh = 270270.2703 mAh
2000	7.4	2000 Wh = 540540.5405 mAh
3000	11.1	3000 Wh = 810810.8108 mAh
5000	18.5	5000 Wh = 1351351.3514 mAh
10000	37	10000 Wh = 2702702.7027 mAh
20000	74	20000 Wh = 5405405.4054 mAh
26800	99.16	26800 Wh = 7243243.2432 mAh
50000	185	50000 Wh = 13513513.5135 mAh

When You'll Need This Conversion

Airline battery compliance

Carry-on lithium batteries are limited to 100 Wh without airline approval, and 160 Wh with it.

Comparing power banks honestly

Convert competing mAh claims into watt-hours before deciding.

Device runtime planning

Divide watt-hours by device power draw to estimate hours of use.

Tool battery packs

18 V tool packs quoted in Ah convert to watt-hours the same way.

Pro Tips for Accurate Conversions

Always ask "at what voltage?"

An mAh figure without a voltage is marketing, not a specification.

100 Wh ≈ 27,000 mAh at 3.7 V

The number to remember before flying.

Expect 60–70% real output from a power bank

Voltage boosting and conversion losses eat the rest.

Common Mistakes to Avoid

Comparing mAh across voltages

A 3.7 V and a 12 V pack with the same mAh differ by more than three times in energy.

Convert both to watt-hours first.

Using 5 V instead of cell voltage

Power banks are rated at cell voltage, not USB output voltage.

Use 3.7 V for the rating, then apply a 0.6–0.7 efficiency factor for delivered 5 V charge.

Assuming a bigger battery charges a phone more times

Conversion losses and phone battery size both matter.

Usable Wh ÷ phone battery Wh × 0.85 gives a realistic charge count.

History & Background

Milliamp-hour marketing arrived with mobile phones in the 1990s. Watt-hour labelling became mandatory when aviation authorities needed a consistent way to regulate lithium battery energy in the cabin.