Wh to mAh Calculator - Battery Energy to Capacity

Agarapu Ramesh — Editor and content reviewer
Editorially reviewed Reviewed by Agarapu Ramesh, science educator (chemistry). LinkedIn
Last reviewed: May 2026 | Standard electrical engineering formulas

Wh is energy. mAh is charge capacity. To convert Wh to mAh, you need battery voltage. Without voltage, the answer is just a guess with extra digits.

Formula at a glance

  • mAh = Wh x 1000 / V
  • Wh = mAh x V / 1000
  • Ah = Wh / V

Field note: A giant mAh number can be marketing noise. Wh is the cleaner way to compare batteries with different voltages.

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Wh to mAh Calculator

Wh
V
Result
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Related Calculators

Mah To Wh Watts To Kwh Energy Consumption Joules To Watts Power Calculator

Common Voltages

Li-ion: 3.7V nominal
Li-Po: 3.7V nominal
NiMH: 1.2V per cell
Lead-acid: 2V per cell

How to use the Wh to mAh Calculator

Use this as a runtime estimate, then discount it for battery age, discharge rate, temperature and inverter losses. Battery labels are optimistic on their best day.

Worked example

Example: 37 Wh at 3.7 V is 10,000 mAh. The same 37 Wh at 12 V is 3,083 mAh.

Practical checks before you trust the number

  • Use nominal pack voltage, not USB output voltage unless that is what you are comparing.
  • Conversion losses mean delivered mAh can be lower than cell mAh.
  • Airline battery rules usually use Wh because voltage can vary.

Common mistake

A giant mAh number can be marketing noise. Wh is the cleaner way to compare batteries with different voltages.

Sources and references

Related calculators

Frequently Asked Questions

mAh = (Wh × 1000) ÷ V. Convert Wh to mWh, then divide by voltage. Example: 50 Wh at 3.7 V → (50 × 1000) ÷ 3.7 = 13,514 mAh. This is how you back-convert from energy ratings to charge ratings for cell selection.

mAh = (Wh × 1000) ÷ V. Voltage required because Wh is energy and mAh is charge. Example: 25 Wh at 5 V → 5000 mAh. Same 25 Wh at 12 V → 2083 mAh. Higher voltage means lower mAh for the same energy.

mAh = (50 × 1000) ÷ 3.7 = 13,514 mAh. So a 50 Wh battery at 3.7 V Li-ion has about 13,500 mAh of charge capacity. This kind of conversion is common when reading laptop or drone battery specs.

Same reason as the reverse: charge (mAh) and energy (Wh) are different physical quantities, linked by voltage. Without voltage, the conversion is undefined. Always specify the cell or pack voltage when converting energy ratings to charge ratings.

Wh is the energy stored — universal across chemistries. mAh is charge capacity at a specific voltage. Two batteries with the same Wh can have very different mAh if their voltages differ. Always compare on Wh for fair energy comparison; use mAh only within a single chemistry/voltage class.

Yes. Most power banks use 3.7 V Li-ion cells internally and report mAh at that voltage. So a 100 Wh power bank = (100 × 1000) ÷ 3.7 = 27,027 mAh nominal. The output through USB at 5 V will deliver less mAh due to the boost converter inefficiency — typically 70 to 80%.

Yes. Useful when manufacturers list one but not the other. Convert Wh ÷ V × 1000 to get mAh, or use the inverse for Wh. Always check the cell voltage assumption — laptop batteries vary from 7.2 V to 14.8 V depending on cell count and configuration.