Convert battery capacity between mAh and Wh, check airline carry-on limits and see how many phone charges a power bank really gives.
This free mAh to Wh converter turns a battery's milliamp-hour rating into watt-hours, and Wh back into mAh. Use it to
check whether a power bank or camera battery is allowed on a plane under the 100 Wh and 160 Wh airline rules, to
compare batteries with different voltages, and to see how many phone charges a power bank really gives.
mAh to Wh formula
Wh = mAh × V ÷ 1000
mAh = Wh × 1000 ÷ V
Milliamp-hours (mAh) measure charge, not energy, so you need the voltage to compare batteries. Watt-hours (Wh) are the
true measure of stored energy — that's why airlines set their limits in Wh.
mAh to Wh chart for common power bank sizes
Energy at 3.7 V, whether the power bank can go in carry-on luggage, and roughly how many charges it gives a
4,500 mAh phone at 85% efficiency.
How many phone charges will I get?
Phone charges = (power bank Wh × efficiency) ÷ phone battery Wh. A 74 Wh bank at 85% efficiency delivers about 63 Wh. A
4,500 mAh phone battery at 3.85 V holds 17.3 Wh, so you get about 3.6 charges — not the 4.4 that
comparing mAh numbers directly suggests.
Related calculations
Frequently asked questions
How do I convert mAh to Wh?
Multiply mAh by the battery voltage and divide by 1000. A 20,000 mAh power bank with 3.7 V cells holds 20,000 × 3.7 ÷ 1000 = 74 Wh.
How do I convert Wh to mAh?
Multiply Wh by 1000 and divide by the voltage: mAh = Wh × 1000 ÷ V. A 100 Wh battery at 3.7 V is 100 × 1000 ÷ 3.7 ≈ 27,027 mAh. Type a value in the Wh box above to convert it.
How many Wh is a 10,000 mAh power bank?
At the standard 3.7 V cell voltage, 10,000 mAh is 37 Wh. That is well under the 100 Wh airline limit and gives about 1.8 charges of a 4,500 mAh phone after conversion losses.
What is the biggest power bank I can take on a plane?
Without airline approval, up to 100 Wh — about 27,027 mAh at 3.7 V. That is why many large power banks are rated just under it, at 26,800 mAh (99.2 Wh). Between 100 and 160 Wh you need the airline's approval.
Can I take a 20,000 mAh power bank on a plane?
Yes, in most cases. At the standard 3.6–3.7 V cell voltage, 20,000 mAh is about 72–74 Wh, below the 100 Wh limit for carry-on without airline approval. Power banks and spare lithium batteries must always go in carry-on luggage, never in checked bags.
What is the airline limit for power banks?
Under FAA and IATA rules, lithium-ion batteries up to 100 Wh are allowed in carry-on. Batteries from 100 to 160 Wh need airline approval and are usually limited to two spares. Batteries over 160 Wh are not allowed on passenger aircraft. Individual airlines can be stricter, so check before you fly.
Why does my 10,000 mAh power bank not charge my phone 3 times?
The mAh rating is at the internal cell voltage (about 3.7 V), but USB delivers 5 V or more, and the voltage conversion wastes 10–20%. A 10,000 mAh bank really delivers about 6,000 mAh at 5 V — enough for roughly 1.5–2 charges of a modern phone.
What voltage should I use?
Use the nominal cell voltage printed on the battery: 3.6–3.7 V for most lithium-ion power banks and phones, 3.85 V for many newer phones, 3.2 V for LiFePO4, 1.2 V for NiMH and 12 V for a car battery.