mAh to Wh Converter
mAh ↔ Wh at the battery’s voltage, power-bank output and the airline Wh limits.
How it was calculated
Air travel (lithium-ion)
IATA Dangerous Goods Regulations (67th edition), IATA’s guidance for passengers travelling with lithium batteries and FAA PackSafe. Airlines and countries can set stricter limits on carrying and using power banks — check with your airline before you fly.
| Capacity | Energy | On a plane |
|---|
Power bank: what reaches your phone
About the mAh to Wh Converter
Milliamp-hours say how much charge a battery holds; watt-hours say how much energy, and you need the battery’s voltage to get from one to the other: Wh = mAh × V ÷ 1000. A 10,000 mAh power bank with 3.7 V cells holds 37 Wh, and a 100 Ah, 51.2 V home battery holds 5.12 kWh.
The converter works both ways, and it tells you what that means in practice: how much a power bank really delivers at its 5 V USB port after conversion losses, how many times that refills a phone, and whether you may take it on a plane. Up to 100 Wh is allowed in carry-on; spare batteries of 101–160 Wh need the airline’s approval (two at most); nothing over 160 Wh may go in passenger baggage. Power banks have tighter limits under IATA’s passenger guidance: two per person and none over 100 Wh.
How to use it
- Choose mAh → Wh or Wh → mAh, and enter the capacity (mAh or Ah) or the energy (Wh or kWh).
- Enter the battery’s nominal voltage, or tap a preset: 3.6–3.85 V for most lithium-ion cells and power banks, 3.2 V for LiFePO4, 12 V or 12.8 V for 12 V batteries. Use the cell voltage, not the 5 V USB output.
- Under Air travel, say whether it is a power bank, a spare battery (camera, laptop, drone) or sits inside a device, and how many you carry, to see how airlines treat it.
- Under Power bank, enter the bank’s capacity and, if you like, your phone’s battery, to see what reaches the phone. If the label prints a “rated capacity” at 5 V, enter it and the calculator uses the real efficiency instead of an assumption.
Examples
10,000 mAh at 3.7 V
10,000 × 3.7 ÷ 1000 = 37 Wh — allowed in carry-on (two power banks at most under IATA’s passenger guidance)
26,800 mAh at 3.7 V
99.16 Wh — under the 100 Wh limit; at 3.85 V the same mAh would be 103.2 Wh, so check the voltage on the label
30,000 mAh at 3.7 V
111 Wh — over 100 Wh, so IATA’s passenger guidance does not accept it as a power bank; a spare battery of this size needs the airline’s approval
100 Ah at 51.2 V (LiFePO4)
5,120 Wh = 5.12 kWh
99 Wh at 3.7 V
99 ÷ 3.7 × 1000 = 26,757 mAh
37 Wh of cells, 80% conversion, 5 V output
29.6 Wh = 5,920 mAh at 5 V — about 1.4 charges of a 5,000 mAh, 3.85 V phone battery (90% charging efficiency)
The formulas
- mAh to Wh: Wh = mAh × V ÷ 1000 (Ah × V for amp-hours)
- Wh to mAh: mAh = Wh ÷ V × 1000
- kWh: kWh = Wh ÷ 1000
- Power bank at its output: Wh_out = Wh_cells × η and mAh_out = Wh_out ÷ V_out × 1000
- Phone charges: n = Wh_out × η_phone ÷ Wh_phone
The voltage is the battery’s nominal voltage: the rated energy printed on lithium-ion batteries is the rated capacity multiplied by the nominal voltage (IEC 61960-3), and the FAA tells travellers to work out Wh the same way — volts times amp-hours.
Lithium-ion batteries on passenger flights
These are the international rules (IATA Dangerous Goods Regulations, 67th edition, Table 2.3.A), IATA’s passenger guidance and the FAA’s PackSafe guidance:
- Spare batteries up to 100 Wh: carry-on baggage only, never checked — take them out of a cabin bag that is checked at the gate — with the terminals protected from short circuit. IATA allows up to 20 spares per person unless the airline approves more.
- Spare batteries over 100 Wh, up to 160 Wh: only with the airline’s approval, at most two per person, in carry-on only.
- Power banks: carry-on only. IATA’s passenger guidance limits each passenger to two power banks of up to 100 Wh, lists power banks over 100 Wh as forbidden, and says they must not be recharged from the aircraft’s power, should not go in the overhead locker and should not power other devices during taxi, take-off and landing. IATA calls these proposed limits that airlines are adopting ahead of the regulations; the FAA still treats power banks as spare batteries, so a 101–160 Wh one needs the airline’s approval in the US.
- Over 160 Wh: not allowed in passenger baggage — it must travel as cargo. Mobility aids such as wheelchairs have their own rules.
- Devices with batteries up to 100 Wh are permitted in carry-on and checked baggage (switched completely off in checked bags); IATA allows up to 15 per person and advises keeping them with you in the cabin. Devices with 101–160 Wh batteries need the airline’s approval.
Airlines and countries can set stricter limits on carrying and using power banks. Check with your airline before you fly.
Why a 10,000 mAh power bank does not charge a 5,000 mAh phone twice
The big number on a power bank is the capacity of its cells at about 3.7 V. Its USB port works at 5 V (or 9–20 V for fast charging), so the same energy is fewer milliamp-hours there — 10,000 mAh at 3.7 V is 7,400 mAh at 5 V before any losses. The boost converter, the cable and the phone’s own charging circuit then lose some more. Some power banks print a “rated capacity” for the output, such as 6,000 mAh at 5 V; enter it and the calculator works out the real conversion efficiency from it.
Sources
- IATA, Dangerous Goods Regulations, 67th edition, Table 2.3.A — provisions for dangerous goods carried by passengers or crew
- IATA, Guidance Document for Passengers Travelling with Lithium Batteries — power banks, Table 1
- FAA PackSafe, Lithium Batteries
- IEC 61960-3:2017, Secondary lithium cells and batteries for portable applications — rated capacity and rated energy
Limitations
- Airline rules here are the IATA and FAA baseline. Individual airlines and countries can set lower limits or ban power banks in flight, and the rules change — check before you travel.
- Non-rechargeable lithium metal batteries are limited by lithium content (2 g per battery for passengers), not watt-hours, so this calculator does not classify them.
- Power-bank efficiency is an estimate unless you enter the rated output capacity from the label; it also changes with the output voltage, the current and the temperature.
- Nominal voltage is an average; a battery’s voltage falls as it discharges, so the energy you get also depends on the load and the cut-off voltage.
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Frequently asked questions
How many Wh is a 20,000 mAh power bank?
At the usual 3.7 V cell voltage, 20,000 × 3.7 ÷ 1000 = 74 Wh — under the 100 Wh limit, so you can take it in your carry-on (not in checked bags). At 3.85 V it is 77 Wh. IATA’s passenger guidance allows two power banks per person.
What is the biggest power bank I can take on a plane?
A power bank of up to 100 Wh: about 27,000 mAh at 3.7 V (100 ÷ 3.7 × 1000 = 27,027 mAh). IATA’s passenger guidance does not accept power banks over 100 Wh and allows two per person. The FAA still lets you carry up to two spare batteries of 101–160 Wh with the airline’s approval, but airlines are adopting the IATA limit — ask yours before flying with anything larger.
Why use 3.7 V and not 5 V?
The mAh rating is for the cells inside, which work at about 3.6–3.85 V. Using the 5 V USB voltage overstates the energy by about 35% — and airlines check the watt-hours at the cell voltage, as printed on the label.
How do I convert Ah to kWh?
Multiply the amp-hours by the voltage and divide by 1000. A 100 Ah, 12.8 V LiFePO4 battery holds 1.28 kWh; a 100 Ah, 51.2 V one holds 5.12 kWh.
How many times will my power bank charge my phone?
Divide the energy that reaches the phone by the phone battery’s energy. A 10,000 mAh, 3.7 V bank (37 Wh) at 80% conversion delivers 29.6 Wh; after 90% charging efficiency, that refills a 5,000 mAh, 3.85 V phone battery (19.25 Wh) about 1.4 times.