mAh to Wh Converter

The mAh to Wh Converter turns a battery's capacity in milliamp-hours (mAh) into watt-hours (Wh) using its voltage — and then does the one thing most converters skip: it tells you whether that battery or power bank is allowed on a plane. Enter a capacity and voltage (or pick a battery-type preset) and you instantly get the watt-hour figure, the FAA/IATA carry-on verdict on a visual gauge, the usable mAh you would actually get at a 5 V USB port, and relatable run-time estimates. It also works in reverse (Wh to mAh).

mAh to Wh Formula

Watt-hours are just charge multiplied by voltage. Because mAh are milli-amp-hours, you divide by 1000 to get the answer in watt-hours:

Example: a 20,000 mAh power bank built from 3.7 V lithium cells stores \( \frac{20000 \times 3.7}{1000} = 74 \) Wh of energy.

Why Convert mAh to Wh at All?

mAh measures electric charge, and charge alone does not tell you how much energy a battery holds — a 10,000 mAh battery at 3.7 V holds half the energy of a 10,000 mAh battery at 7.4 V. Watt-hours fold voltage into the number, so they measure true energy and let you compare any two batteries fairly. That is exactly why airlines, shipping couriers, and manufacturers all quote limits in Wh rather than mAh.

Airline Rules for Batteries and Power Banks

Air-travel rules for spare lithium batteries and power banks are written around two watt-hour thresholds. This calculator checks your result against both automatically:

Spare batteries and power banks must always travel in your carry-on, never in checked luggage. Rules can vary slightly by carrier and country, so treat this as a guide and confirm with your airline before you fly.

What Voltage Should I Use?

Use the battery's nominal voltage — the average voltage the pack holds while discharging, not the fully charged peak. Common values:

Power Bank mAh vs Usable mAh

Here is the detail that confuses most shoppers. A power bank labelled "20,000 mAh" measures that charge at its internal cell voltage (~3.7 V). But it charges your phone through a 5 V USB port, and stepping the voltage up loses roughly 10–15% to heat. So the mAh you actually receive at 5 V is much lower — often around 12,000–13,000 mAh from a "20,000 mAh" bank. The energy in watt-hours does not change; only the mAh figure does, because mAh depends on voltage. This tool estimates that usable figure for you.

How to Use This Calculator

1. Choose a direction: mAh to Wh (the default) or Wh to mAh for the reverse.
2. Enter the capacity: type the mAh (or switch the unit to Ah), or the energy in Wh for the reverse direction.
3. Enter the voltage: type the nominal voltage, or click a battery-type preset to fill it in.
4. Review the result: read the watt-hour value, the airline verdict on the gauge, usable mAh at 5 V, real-world estimates, and the step-by-step formula.

Frequently Asked Questions

How do you convert mAh to Wh?

Multiply the capacity in milliamp-hours by the battery voltage, then divide by 1000: Wh = (mAh × V) / 1000. For example, a 20,000 mAh power bank at 3.7 V holds 20000 × 3.7 / 1000 = 74 Wh.

What voltage should I use for a power bank?

Most power banks rate their mAh at the internal lithium cell voltage of about 3.6 to 3.7 V, so use 3.7 V unless the label states otherwise. The 5 V printed on the USB port is the output voltage, not the rating voltage.

How many watt-hours can I take on a plane?

Spare lithium batteries and power banks up to 100 Wh are allowed in carry-on with no approval. From 100 Wh to 160 Wh you need airline approval and may carry at most 2 spares. Over 160 Wh they are banned from passenger aircraft.

Why is my usable mAh lower than the label?

A power bank stores energy at about 3.7 V but delivers it through a 5 V USB port with conversion losses of roughly 10 to 15 percent. So a 20,000 mAh bank delivers closer to 12,000 to 13,000 mAh at 5 V, even though the energy in Wh is unchanged.

How do you convert Wh back to mAh?

Multiply the watt-hours by 1000 and divide by the voltage: mAh = (Wh × 1000) / V. For example, 74 Wh at 3.7 V equals 74 × 1000 / 3.7 = 20,000 mAh.

What is the difference between mAh and Wh?

mAh (milliamp-hours) measures electric charge and depends on voltage, while Wh (watt-hours) measures energy and is voltage-independent. Wh is the fair way to compare batteries of different voltages, which is why airlines and shipping rules use Wh.

Additional Resources

• Ampere-hour - Wikipedia
• Watt-hour / Kilowatt-hour - Wikipedia