Question 1

How do you convert mAh to Wh?

Accepted Answer

Multiply the capacity in mAh by the battery's voltage, then divide by 1,000: Wh = mAh × V ÷ 1,000. For example, a 20,000 mAh power bank at 3.7 V holds 20,000 × 3.7 ÷ 1,000 = 74 Wh. To go from Wh back to mAh, multiply by 1,000 and divide by the voltage.

Question 2

Why do I need the voltage to convert mAh to Wh?

Accepted Answer

Because mAh measures charge, not energy. Two batteries with the same mAh but different voltages store different amounts of energy. Watt-hours combine charge and voltage, which is why Wh is the fairer way to compare batteries — and why airlines rate carry-on power banks in Wh.

Question 3

What voltage should I use for a power bank?

Accepted Answer

Most power banks are built from 3.7 V lithium-ion cells, so the mAh on the label is usually at 3.7 V — that's the number to use for the Wh capacity, even though the USB output is 5 V. The Wh figure (often printed near the airline-limit text) is the true energy. When in doubt, use the voltage printed on the battery.

Question 4

How many Wh can I take on a plane?

Accepted Answer

US and international rules generally allow lithium power banks up to 100 Wh in carry-on without approval, 100–160 Wh with airline approval, and ban anything over 160 Wh. A 20,000 mAh bank at 3.7 V is 74 Wh, so it's fine — converting mAh to Wh tells you instantly whether a battery is allowed.

mAh to Wh Calculator

Frequently asked questions

Related tools

Related converters

Ah ↔ kWh

Watts ↔ Amps

kW ↔ Amps

Volts ↔ Watts

Sources & standards