Introduction
Electric charge is measured in coulombs (C) in SI; the ampere-hour (Ah) is the practical unit for batteries. One coulomb is the charge transferred by one ampere flowing for one second. An AA battery holds ~2.5 Ah (9,000 C) of charge at 1.5 V. An iPhone 15 battery is ~3.3 Ah at 3.87 V = 12.8 Wh of energy.
Why electric charge units exist and how they diverged
The coulomb (C) is the SI unit of charge, defined as the charge of 6.242 × 10¹⁸ elementary charges (electrons or protons). The ampere-hour (Ah) = 3,600 C is more practical for batteries — a battery rated 3,000 mAh delivers 3 Ah = 10,800 C. Battery capacity in Ah doesn't tell you energy directly; multiply by voltage to get watt-hours.
How to convert electric charge
Ah to coulombs: multiply by 3,600. mAh to Ah: divide by 1,000. Battery energy (Wh) = capacity (Ah) × voltage (V).
Units supported by this electric charge calculator
- Coulomb (C)
- Millicoulomb (mC)
- Microcoulomb (µC)
- Nanocoulomb (nC)
- Ampere-hour (Ah)
- Milliampere-hour (mAh)
- Abcoulomb
- Statcoulomb (esu)
- Elementary charge (e)
- Faraday constant
Common electric charge conversion mistakes
- Ah vs Wh. Ah is charge capacity; Wh is energy. An 18650 cell rated 3,500 mAh at 3.7 V has 13 Wh. A 12 V car battery rated 50 Ah has 600 Wh. You can't compare 3,500 mAh to 50 Ah without accounting for voltage.
- mAh in phone batteries. At the phone's 3.87 V nominal, not at 5 V (USB). Converting to watt-hours requires the battery voltage, not the charging voltage.
- Coulomb as a large unit. 1 C is huge — a lightning bolt transfers ~5-30 C.
Real-world electric charge examples
- 1 electron's charge: 1.602 × 10⁻¹⁹ C.
- AA alkaline: 2.5 Ah (9,000 C) at 1.5 V.
- iPhone 15 battery: 3,349 mAh = 3.35 Ah at 3.87 V nominal = 12.8 Wh.
- Tesla Model 3 battery: ~190 Ah at 350-400 V = 75 kWh.
- Car starter battery: 50-80 Ah at 12 V = 600-960 Wh.
- Lightning bolt: 5-30 C total charge transferred.
Tips for accurate electric charge conversion
- Compare batteries by Wh (energy), not mAh or Ah. Voltage matters.
- For phone banks, a '20,000 mAh power bank' at 3.7 V is 74 Wh. Airline carry-on limit is typically 100 Wh per battery.
Related: Electric Current Converter · Capacitance Converter · Energy Converter.