mAh to Wh Calculator

Convert milliamp-hours to watt-hours for any battery voltage and see the true energy capacity of phones, laptops, drones, and power banks. Wh is also how airlines measure carry-on battery limits, so this is the number you need before flying with a lithium pack.

Battery Capacity (mAh)

Battery Voltage (V)

= 18.5 Wh

See full breakdown for 5,000mAh at 3.7V

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What Is mAh vs Wh?

mAh (milliamp-hours) measures charge capacity: how much current a battery can deliver for how long. Wh (watt-hours) measures energy capacity: how much total work the battery can do. The difference is voltage. A 5000 mAh battery at 3.7V stores 18.5 Wh. The same 5000 mAh at 12V stores 60 Wh. Same charge, very different energy.

The Formula

Wh = (mAh × Voltage) ÷ 1000

You must know the battery's nominal cell voltage to convert accurately. Phone batteries and USB power banks are both 3.7V Li-ion internally, even though power banks expose a 5V USB output to charge downstream devices. The advertised mAh on a power bank is always quoted at the 3.7V cell, so use 3.7V here. Laptop batteries are typically 7.4V (2S), 11.1V (3S), or 14.8V (4S) depending on how many cells are wired in series. Lead-acid car batteries are 12V.

Why Wh Matters

Airline travel: FAA and ICAO passenger-aircraft rules tier lithium-ion batteries in watt-hours: up to 100 Wh is generally allowed in carry-on without airline approval; 100-160 Wh typically requires airline approval and is limited to a small number of spares per passenger; above 160 Wh is generally not permitted in normal passenger baggage. Spare batteries must travel in carry-on with terminals protected, and airlines can impose stricter limits on top of the baseline, so always check your carrier's dangerous-goods page. A 27,000 mAh power bank at 3.7V works out to 99.9 Wh nominal, landing in the first tier.
Comparing batteries: A 10,000 mAh phone bank (3.7V = 37 Wh) stores less energy than a 5,000 mAh laptop battery (11.1V = 55.5 Wh) despite the higher mAh rating.
Device runtime: Runtime (hours) = usable Wh ÷ device power draw (W), where usable Wh is typically 80-90% of nominal after DC-DC conversion and chemistry losses. A 37 Wh battery at 85% usable powers a 2W device for roughly 15-16 hours.

Common Battery Capacities

Device	Typical mAh	Voltage	Wh
Smartphone	4,500 mAh	3.7V	16.65 Wh
Power Bank (small)	10,000 mAh	3.7V	37 Wh
Power Bank (large)	20,000 mAh	3.7V	74 Wh
Laptop Battery	5,000 mAh	11.1V	55.5 Wh
Drone Battery	3,000 mAh	11.1V	33.3 Wh
Car Battery	50,000 mAh	12V	600 Wh
E-Bike Battery	15,000 mAh	48V	720 Wh

Related Calculators

Frequently Asked Questions

How do I convert mAh to Wh?expand_more

Wh = (mAh × Voltage) ÷ 1000. For example, a 5000 mAh battery at 3.7V has 18.5 Wh of energy. You need to know the battery voltage to convert.

Why do batteries show mAh instead of Wh?expand_more

mAh measures charge capacity (how much current for how long). Wh measures energy capacity (how much work the battery can do). mAh is simpler but Wh is more useful for comparing batteries at different voltages.

What voltage should I use for phones and power banks?expand_more

Always use 3.7V, the nominal Li-ion cell voltage. Phones, tablets, and USB power banks all print their mAh rating at 3.7V cell capacity, not the 5V USB output. Using 5V instead of 3.7V overstates Wh by about 35% and can wrongly push a 99 Wh pack past the 100 Wh tier where airline approval typically kicks in.

How does mAh relate to battery life?expand_more

mAh alone does not give you runtime; you need a watt load or the device voltage as well, because mAh is charge and runtime depends on energy. Convert to Wh first (Wh = mAh × V ÷ 1000), apply a usable-energy factor of about 85% to account for DC-DC conversion and chemistry losses, then divide by the device wattage: usable hours ≈ (Wh × 0.85) ÷ device watts. A 5,000 mAh cell at 3.7V holds 18.5 Wh nominal (about 15.7 Wh usable) which powers a 2W load for roughly 7.9 hours.

What is the FAA limit for batteries on planes?expand_more

The FAA and ICAO set three lithium-ion passenger-aircraft tiers by watt-hours, each with conditions rather than flat numeric rules: batteries up to 100 Wh are generally allowed in carry-on without airline approval; 100-160 Wh typically requires airline approval and is limited to a small number of spares per passenger; batteries over 160 Wh are generally not permitted in normal passenger baggage. Spare (uninstalled) batteries must travel in carry-on with terminals protected against short circuits, not in checked baggage; installed batteries inside a device follow different rules than spares; and individual airlines can impose stricter limits on top of the FAA/ICAO baseline. A 27,000 mAh power bank at 3.7V works out to 99.9 Wh nominal, which lands in the first tier, but the carrier's dangerous-goods page is the authoritative source for any specific trip.

This calculator provides estimates for reference purposes only. Actual battery capacity may vary with age, temperature, and discharge rate.

Standards & References

This page cites the following electrical codes and standards. Always consult the current edition of your local adopted standard for authoritative requirements.

FAA PackSafe: Lithium Batteries. Lithium-ion batteries in carry-on baggage: up to 100 Wh without airline approval; 100-160 Wh with airline approval; above 160 Wh prohibited.
Federal Aviation Administration. Reference →
UN 38.3. UN Manual of Tests and Criteria, Section 38.3. Required safety testing protocol for lithium cells and batteries shipped internationally: altitude simulation, thermal test, vibration, shock, external short circuit, impact, overcharge, and forced discharge.
United Nations Economic Commission for Europe. Reference →
DOT 49 CFR 173.185. US Department of Transportation hazardous materials regulation for lithium cells and batteries. Covers watt-hour limits, packaging, labeling, and quantity thresholds for ground, rail, and vessel transport within the US.
US Department of Transportation / PHMSA. Reference →
IATA Dangerous Goods Regulations. International rules for the air transport of dangerous goods, including lithium batteries. Defines watt-hour thresholds for passenger aircraft (spare batteries in carry-on only, 100/160 Wh tiers) and cargo aircraft shipments.
International Air Transport Association. Reference →

Disclaimer: The information on this page is provided for reference. Always consult a licensed electrician and the current edition of your local adopted electrical code before performing electrical work.