To convert mAh to Wh, multiply mAh by the battery voltage and divide by 1,000. A 10,000 mAh power bank at 3.7 V holds 37 Wh; a 20,000 mAh bank holds 74 Wh. Airlines set limits in watt-hours: up to 100 Wh is fine in carry-on, 101–160 Wh needs approval.
Battery capacity in mAh only makes sense with a voltage. Watt-hours (Wh) measure the energy actually stored, so they're what airlines, laptops and power stations use. Convert between mAh, Ah and Wh at any voltage, check airline limits and estimate runtime.
How to use this calculator
- Enter the capacity printed on the battery and pick its unit: mAh, Ah or Wh.
- Choose the nominal voltage. For phones and power banks use the cell voltage on the label (usually 3.7 V or 3.85 V), not the 5 V USB output.
- Read the energy in Wh, the equivalent mAh and Ah, and the flight rule that applies.
- Optionally enter the power draw of your device in watts to estimate runtime and phone charges.
How it's calculated
The FAA gives the rule directly: to calculate watt-hours, multiply the battery voltage by the amp-hours. Since 1 Ah = 1,000 mAh:
Wh = mAh × V ÷ 1000— V is the nominal voltage, mAh the rated capacity.mAh = Wh × 1000 ÷ V— the reverse, for labels that only give Wh.Ah = mAh ÷ 1000Runtime (h) = Wh × efficiency ÷ device watts— efficiency is an assumption (85%) covering voltage conversion and heat losses. Real losses vary by device and cable.
The flight check uses the FAA and 49 CFR 175.10(a)(18) thresholds: up to 100 Wh allowed, 101–160 Wh allowed with airline approval (two spares at most), over 160 Wh forbidden in passenger baggage.
Worked examples
1. A 26,800 mAh power bank
26,800 × 3.7 ÷ 1000 = 99.16 Wh. That is just under 100 Wh, so it can fly in carry-on without airline approval. Driving a 10 W load it would run for about 8.4 hours at 85% efficiency.
2. A 5,000 mAh phone battery at 3.85 V
5,000 × 3.85 ÷ 1000 = 19.25 Wh. If your phone battery is rated at 3.85 V, use that; 3.7 V instead would give 18.5 Wh, a small but real difference.
3. A 99 Wh laptop battery, in mAh
At 11.1 V (a three-cell pack), 99 Wh × 1000 ÷ 11.1 = 8,919 mAh. At 3.7 V the same energy would read 26,757 mAh. The Wh figure stays the same; the mAh number changes with voltage. That is why airlines ask for Wh.
mAh to Wh chart (3.7 V)
Common power bank and phone capacities at the standard 3.7 V lithium-ion cell voltage, with the FAA carry-on status for each.
| Capacity | Wh @ 3.7 V | Wh @ 3.85 V | Carry-on? |
|---|---|---|---|
| 3,000 mAh | 11.1 | 11.55 | Yes |
| 4,000 mAh | 14.8 | 15.4 | Yes |
| 5,000 mAh | 18.5 | 19.25 | Yes |
| 10,000 mAh | 37 | 38.5 | Yes |
| 15,000 mAh | 55.5 | 57.75 | Yes |
| 20,000 mAh | 74 | 77 | Yes |
| 25,000 mAh | 92.5 | 96.25 | Yes |
| 26,800 mAh | 99.16 | 103.18 | Yes |
| 27,000 mAh | 99.9 | 103.95 | Yes |
| 30,000 mAh | 111 | 115.5 | With airline approval |
| 40,000 mAh | 148 | 154 | With airline approval |
| 50,000 mAh | 185 | 192.5 | No |
Wh to mAh chart at common voltages
Use this when a label gives only watt-hours, or to see what 100 Wh and 160 Wh mean in mAh for different packs.
| Wh | 3.7 V | 7.4 V | 11.1 V | 14.8 V |
|---|---|---|---|---|
| 10 Wh | 2,703 mAh | 1,351 mAh | 901 mAh | 676 mAh |
| 20 Wh | 5,405 mAh | 2,703 mAh | 1,802 mAh | 1,351 mAh |
| 50 Wh | 13,514 mAh | 6,757 mAh | 4,505 mAh | 3,378 mAh |
| 74 Wh | 20,000 mAh | 10,000 mAh | 6,667 mAh | 5,000 mAh |
| 99 Wh | 26,757 mAh | 13,378 mAh | 8,919 mAh | 6,689 mAh |
| 100 Wh | 27,027 mAh | 13,514 mAh | 9,009 mAh | 6,757 mAh |
| 160 Wh | 43,243 mAh | 21,622 mAh | 14,414 mAh | 10,811 mAh |
Airline battery rules in plain English
The FAA's PackSafe guidance and 49 CFR 175.10(a)(18) set the limits for passengers on US flights:
- Up to 100 Wh per battery: allowed. The FAA says this covers nearly all lithium batteries the average person uses in their electronic devices.
- 101–160 Wh: allowed with airline approval, maximum two spare batteries per person.
- Over 160 Wh: forbidden in passenger baggage.
- Spares and power banks go in carry-on only. If a bag is checked at the gate or planeside, take spare batteries out and keep them in the cabin. TSA also lists power banks as carry-on yes, checked no.
- Protect the terminals from short circuit: retail packaging, tape over the terminals, a battery case or sleeve, or a snug plastic bag or pouch.
- Lithium metal (non-rechargeable) batteries are limited by lithium content instead of Wh: 2 grams per battery, or up to 8 grams with airline approval.
- Damaged or recalled batteries must not be carried unless removed or made safe.
The FAA notes that many airlines set stricter limits, including how many power banks each passenger may carry, whatever their Wh rating. Check your airline before you fly. The flight result in this calculator is general information, not a ruling on your specific battery.
Common mistakes
- Using 5 V for a power bank. The mAh on a power bank is normally quoted at the internal cell voltage (commonly 3.7 V), not the output voltage. Using the 5 V USB output voltage overstates the energy by about a third and can make a legal bank look over the limit.
- Comparing mAh across voltages. A 2,000 mAh 11.1 V drone pack holds three times the energy of a 2,000 mAh 3.7 V cell. Compare in Wh.
- Expecting 100% of the rating. Charging a phone involves stepping voltage up and back down, and some energy is lost as heat. The 85% figure here is an assumption, not a measured value for your device.
- Ignoring the printed Wh. If the battery states Wh, use that number. The FAA notes that newer lithium ion batteries have the Wh rating marked on them.
mAh vs Wh: which should you compare?
Compare mAh only between batteries of the same voltage, such as two phone power banks built on 3.7 V cells. For anything else, including laptop packs, drone batteries, e-bike packs, portable power stations or a 12 V leisure battery, convert to Wh first. Wh is also what you need to work out runtime, since device power is quoted in watts. For 12 V and 24 V systems, sizing the cable matters as much as the battery; see the wire size calculator.
Frequently asked questions
How do you convert mAh to Wh?
Wh = mAh × V ÷ 1000. A 20,000 mAh power bank at 3.7 V holds 20,000 × 3.7 ÷ 1000 = 74 Wh.
How do you convert Wh to mAh?
mAh = Wh × 1000 ÷ V. 100 Wh at 3.7 V is 27,027 mAh.
How many Wh is 10,000 mAh?
At the usual 3.7 V cell voltage, 10,000 mAh is 37 Wh. At 3.85 V it is 38.5 Wh.
Can I take a 20,000 mAh power bank on a plane?
Yes. At 3.7 V it's 74 Wh, under the FAA's 100 Wh limit. Power banks must go in carry-on, never checked bags. If your carry-on is checked at the gate, take the power bank out and keep it with you. Some airlines limit how many power banks you can bring, so check with yours.
Can I take a 30,000 mAh power bank on a plane?
At 3.7 V a 30,000 mAh bank is 111 Wh. That is over 100 Wh, so under FAA rules you need airline approval, and you may carry no more than two spare batteries in the 101–160 Wh range. Check the Wh figure printed on the bank, because it may use a different voltage.
What is the biggest power bank allowed on a plane?
Up to 100 Wh (about 27,027 mAh at 3.7 V) without approval. From 101 to 160 Wh (about 43,243 mAh) you need airline approval, with a maximum of two spares per person. Batteries over 160 Wh are forbidden in passenger baggage.
Is 27,000 mAh under 100 Wh?
Yes, just. At 3.7 V, 27,000 mAh is 99.9 Wh. The exact 3.7 V limit is 27,027 mAh, and a bank rated at a higher cell voltage crosses 100 Wh sooner.
Why does my power bank deliver less than its mAh rating?
mAh is rated at the 3.7 V cell voltage, but USB outputs 5 V or more, and conversion loses some energy (this calculator assumes 15%). A 10,000 mAh bank then delivers about 6,290 mAh at 5 V.
How many times will a power bank charge my phone?
Divide the bank's Wh by your phone battery's Wh, after allowing for losses. With the calculator's assumptions (85% efficiency, 15 Wh phone battery) a 10,000 mAh bank gives about 2.1 charges and a 20,000 mAh bank about 4.2.
Can lithium batteries go in checked luggage?
Spare lithium batteries and power banks cannot. The FAA requires spare lithium ion and lithium metal batteries, including power banks and phone charging cases, to travel in carry-on baggage only, with the terminals protected from short circuit.
What does mAh mean on a battery?
Milliamp-hours: the charge a battery can deliver, where 1,000 mAh means one amp for one hour. It does not include voltage, so it only compares batteries of the same voltage. Watt-hours include voltage and measure energy.
Sources & method
- FAA PackSafe — Lithium batteries (100 Wh; two spares 101–160 Wh with airline approval; carry-on only; 2 g lithium metal; terminal protection; Wh = V × Ah)
- FAA — Airline passengers and batteries (Wh = V × Ah; over 160 Wh forbidden)
- 49 CFR 175.10(a)(18) — lithium batteries carried by passengers
- TSA — Power banks: carry-on yes, checked no
Results are estimates for general information. Found an error? It helps everyone — see our methodology.