--- title: "mAh to Wh Calculator: Convert mAh to Watt Hours" description: "Convert mAh to Wh and Wh to mAh for phones, power banks and laptops. Wh = mAh × V ÷ 1,000. Check if a power bank is under the 100 Wh airline limit." canonical: https://batteryruntimecalculator.com/mah-to-wh-calculator language: en updated: 2026-11-10 source_revision: 59f9d32 maintainer: Battery Runtime Calculator (hello@batteryruntimecalculator.com) --- # mAh to Wh Calculator Convert milliamp-hours to watt-hours and back for phones, power banks, laptops, drones and any lithium battery. Updated November 10, 2026 Quick answer Wh = mAh × V ÷ 1,000. A 10,000 mAh power bank with 3.7 V cells holds **37 Wh**, and a 20,000 mAh one **74 Wh**, both under the 100 Wh airline carry-on limit. Capacity in watt-hours 37 Wh 10,000 mAh at 3.7 V Under the 100 Wh airline carry-on limit Amp-hours 10 Ah Milliamp-hours 10,000 mAh Watt-hours 37 Wh Kilowatt-hours 0.037 kWh 10,000 mAh × 3.7 V ÷ 1,000 = 37 Wh ## How to convert mAh to Wh Multiply milliamp-hours by the voltage and divide by 1,000: ``` Wh = mAh × V ÷ 1,000 ``` Example: a 5,000 mAh phone battery at 3.85 V holds 5,000 × 3.85 ÷ 1,000 = 19.3 Wh. ## How to convert Wh to mAh ``` mAh = Wh × 1,000 ÷ V ``` Example: a 99 Wh laptop battery at 11.55 V is 99 × 1,000 ÷ 11.55 = 8,571 mAh. Larger batteries are usually rated in amp-hours; the [Ah to Wh calculator](https://batteryruntimecalculator.com/ah-to-wh-calculator) handles those, and 1 Ah = 1,000 mAh. ## Power bank mAh to Wh chart Power banks are rated at the 3.7 V of their lithium-ion cells. Airline rules for spare lithium batteries (FAA and IATA): up to 100 Wh in carry-on only, 100–160 Wh with airline approval, over 160 Wh not allowed. Power banks are never allowed in checked bags. | Power bank | Watt-hours | On a plane | | --- | --- | --- | | 5,000 mAh | 18.5 Wh | Allowed in carry-on | | 10,000 mAh | 37 Wh | Allowed in carry-on | | 20,000 mAh | 74 Wh | Allowed in carry-on | | 26,800 mAh | 99.2 Wh | Allowed in carry-on | | 30,000 mAh | 111 Wh | Needs airline approval | | 40,000 mAh | 148 Wh | Needs airline approval | | 50,000 mAh | 185 Wh | Not allowed | The largest power bank you can fly with without approval is about 27,027 mAh at 3.7 V. Many airlines also limit how many you carry and ban using them in flight, so check your airline before you travel. If the label already shows Wh, that figure is the one security staff go by. ## Watt-hours of common devices | Device | Typical capacity | Voltage | Watt-hours | | --- | --- | --- | --- | | Wireless earbuds case | 500 mAh | 3.7 V | 1.9 Wh | | Smartwatch | 300 mAh | 3.85 V | 1.2 Wh | | Smartphone | 5,000 mAh | 3.85 V | 19.3 Wh | | Tablet | 8,000 mAh | 3.8 V | 30.4 Wh | | Drone battery | 5,000 mAh | 15.4 V | 77 Wh | | Laptop battery | 4,500 mAh | 11.6 V | 52 Wh | Check the label of your own device for exact figures. mAh alone does not compare batteries of different voltages: a 5,000 mAh drone pack holds four times the energy of a 5,000 mAh phone battery, because it has four cells in series. ## Why the 5 V USB output does not change the rating A power bank’s mAh is the capacity of its cells at 3.7 V. When it charges a phone, a converter steps the voltage up to 5 V (or 9–20 V for fast charging), so fewer milliamp-hours come out of the USB port than the label says, even before losses. Watt-hours avoid that confusion, which is why airlines and laptop makers use them. To estimate how long a device runs on a battery, use the [battery life calculator](https://batteryruntimecalculator.com/battery-life-calculator) for mAh and mA, or the [battery runtime calculator](https://batteryruntimecalculator.com/) for Wh and watts. ## Frequently asked questions ### How many Wh is 10,000 mAh? About 37 Wh. Power banks are rated at their internal 3.7 V lithium-ion cell voltage, so 10,000 mAh × 3.7 V ÷ 1,000 = 37 Wh. ### How many Wh is 20,000 mAh? About 74 Wh at 3.7 V, comfortably under the 100 Wh limit for carrying a power bank on a plane without airline approval. ### How many mAh is 100 Wh? About 27,027 mAh at 3.7 V. That is why the largest power banks you can fly with freely are sold as 26,800 mAh: at 3.7 V that is 99.2 Wh, just under the limit. ### Which voltage should I use to convert mAh to Wh? Use the battery’s nominal voltage, printed next to the mAh on the label. For phones, power banks and most lithium-ion packs it is 3.6–3.85 V per cell; laptop and drone packs have several cells in series (7.4 V, 11.1 V, 14.8 V and so on). Do not use the 5 V USB output voltage: the mAh rating refers to the cells, not the USB port. ### Why doesn’t a 10,000 mAh power bank charge a 5,000 mAh phone twice? Because energy is lost converting the 3.7 V cells to 5 V USB and back again inside the phone, usually 30–40% in total. A 10,000 mAh bank holds 37 Wh; a 5,000 mAh phone at 3.85 V holds 19.3 Wh. 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