What Is an Electric Charge Unit Calculator?
Electric charge is measured in coulombs in the SI system, but everyday devices like batteries almost always list their capacity in amp-hours (Ah) or milliamp-hours (mAh). This calculator converts freely between all three, using the exact relationship that defines the ampere itself.
Whether you're comparing a battery datasheet, sizing a power bank, or working through a physics problem, this tool removes the guesswork from switching between charge units.
How to Read Your Results
Coulombs (C)
The SI base unit of electric charge. One coulomb is the amount of charge transported by a steady current of one ampere in one second.
Amp-hours (Ah)
A practical unit for battery capacity: the charge delivered by one amp flowing continuously for one hour. Common on car batteries, solar batteries, and power tools.
Milliamp-hours (mAh)
One-thousandth of an amp-hour, used for smaller batteries like phones, cameras, and portable electronics where amp-hour values would be inconveniently small.
Real-World Example
A smartphone battery is rated at 4,000 mAh. How much charge is that in coulombs?
| Unit | Value |
|---|---|
| Milliamp-hours | 4,000 mAh |
| Amp-hours | 4 Ah |
| Coulombs | 14,400 C |
4,000 mAh equals 4 Ah, and multiplying by 3,600 gives 14,400 coulombs of total charge capacity — the amount the battery can theoretically deliver before it's fully drained.
Tips for Working With Electric Charge
- Charge is not energy — multiply amp-hours by voltage to get watt-hours, the actual energy stored.
- 1 Ah = 3,600 C exactly, since it comes straight from the SI definition of the ampere as coulombs per second.
- Battery capacity ratings are theoretical maximums — real-world usable capacity is usually lower due to voltage sag and discharge efficiency.
- When comparing batteries, make sure you're comparing the same unit (mAh vs Ah) and, ideally, the same nominal voltage.
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Last updated: August 2026 · Reviewed by: Simple Calculator Tools Editorial Team