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Battery Capacity & Watt-Hour Calculator

Convert battery capacity and nominal voltage into watt-hours, or calculate mAh and Ah from watt-hours and voltage. Useful for power banks, electronics and battery-rating checks.

Example: a 10,000 mAh battery has a nominal voltage of 3.7 V. How many watt-hours is that?
Battery energy 37 Wh 10 Ah × 3.7 V = 37 Wh
Equivalent values 10,000 mAh · 10 Ah · 37,000 mWh · 0.037 kWh Capacity and energy are shown in common units for quick comparison.
Air-travel note Use the Wh result as the battery-rating reference Lithium-battery rules can vary by airline and authority; verify current requirements before travel.

✓ FAA guidance calculates watt-hours as volts × ampere-hours; for mAh, divide capacity by 1,000 first

How is it calculated? Nominal battery energy is calculated with Wh = V × Ah. For milliampere-hours, use Wh = V × mAh ÷ 1,000. In reverse, Ah = Wh ÷ V or mAh = Wh × 1,000 ÷ V. This is a nominal rating from rated capacity and nominal voltage, not an exact estimate of usable energy or runtime.

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Battery watt-hour formulas and quick examples

  • Watt-hours: Wh = V × Ah
  • From milliampere-hours: Wh = V × mAh ÷ 1,000
  • Ampere-hours: Ah = Wh ÷ V
  • Milliampere-hours: mAh = Wh × 1,000 ÷ V
  • 10,000 mAh × 3.7 V ÷ 1,000 = 37 Wh
  • 20,000 mAh × 3.7 V ÷ 1,000 = 74 Wh
  • 8 Ah × 12 V = 96 Wh

How it works

  1. Choose whether you want to calculate watt-hours from battery capacity, or calculate capacity from watt-hours.
  2. Enter the battery capacity or energy value, then enter the battery’s nominal voltage.
  3. For capacity to energy, use Wh = V × Ah. If capacity is in mAh, divide by 1,000 first.
  4. For energy to capacity, use Ah = Wh ÷ V or mAh = Wh × 1,000 ÷ V.
  5. Example: 10,000 mAh at 3.7 V equals 37 Wh. In reverse, 37 Wh at 3.7 V equals 10,000 mAh.
  6. The result is a nominal battery rating based on rated capacity and nominal voltage; actual usable energy and runtime depend on the battery, device and operating conditions.
Formula and travel-reference sources

FAQ

How do I convert mAh to Wh?

Multiply mAh by the battery voltage, then divide by 1,000. For example, 10,000 mAh × 3.7 V ÷ 1,000 = 37 Wh.

How do I convert Wh to mAh?

Divide Wh by voltage to get Ah, then multiply by 1,000. For example, 37 Wh ÷ 3.7 V × 1,000 = 10,000 mAh.

Can I convert mAh to Wh without voltage?

No. mAh is electric charge while Wh is energy, so the battery voltage is required to relate them.

Should I use nominal voltage?

Yes. Battery watt-hour ratings are normally calculated from rated capacity and nominal voltage.

Can I use this calculator for airline travel?

You can use it to determine a battery’s Wh rating. Before traveling, compare the result with the current rules from your airline and the relevant aviation authority because requirements can change or be stricter.

Does the calculated Wh equal the exact energy I can use?

Not necessarily. It is a nominal rating; actual usable energy can differ because of conversion losses, discharge conditions, battery age and device behavior.

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