About the Ah to Coulombs Converter
Battery capacity is printed in amp-hours or milliamp-hours, while physics problems use coulombs, the SI unit of electric charge. They measure the same thing: how much charge a battery can move. One amp flowing for one hour is 3,600 coulombs, so one amp-hour is exactly 3,600 C. This converter multiplies your amp-hours by 3,600 and shows the coulombs at once, together with milliamp-hours, millicoulombs, microcoulombs and the equivalent number of elementary charges. Use it for battery capacity questions, electrolysis and charge calculations. It is simple, private and works in your browser.
Updated October 2026
How to use the Ah to Coulombs Converter
- 1Type the charge in amp-hours (Ah).
- 2Read the coulombs at the top of the result.
- 3See mAh, mC, µC and elementary charges in the rows below.
- 4Press Copy to copy the sentence.
- 5Change the number for another battery or value.
The formula
coulombs = amp-hours × 3,600. Because current is charge per time, one amp for 3,600 seconds moves 3,600 coulombs.
To go back, use the Coulombs to Ah converter.
Examples
- 1 Ah = 3,600 C
- 0.5 Ah = 1,800 C
- 2.5 Ah = 9,000 C
- 100 Ah, a typical leisure battery, = 360,000 C
Charge, current and energy
Current in amps is charge per second. Charge in coulombs is current times time. Energy in joules is charge times voltage, so a 12 V, 100 Ah battery holds 360,000 C × 12 V = 4,320,000 J, or 1.2 kWh.
Real batteries cannot always deliver their full rated charge, especially when discharged fast or cold, so use the figure as a guide.
Worked example: a phone battery
A phone battery rated 4.2 Ah, which many labels write as 4,200 mAh, holds 4.2 × 3,600 = 15,120 coulombs. At a steady 0.5 A, that charge lasts 8.4 hours, and at 2 A it lasts 2.1 hours. The coulomb figure does not change with the current, which is why it is a useful way to describe capacity.
For a physics problem, the same charge corresponds to about 9.44 × 10^22 elementary charges, the number you see in the last row of the result.
Rated versus real capacity
The amp-hour figure on a battery is measured under set conditions. Drawing current faster, or using it in the cold, delivers fewer coulombs. Lead-acid batteries are often rated at the 20-hour rate, so a 100 Ah battery gives 5 A for 20 hours but less than 100 Ah if drained in one hour.
Phone and computer
Results appear as you type, in one column on a phone and beside the input on a computer. Going the other way? The Coulombs to Ah Converter reverses the result, and the mAh to Wh Calculator turns the capacity into energy.
Features
- Exact factor: 1 Ah = 3,600 C
- Milliamp-hours, millicoulombs and microcoulombs shown
- Number of elementary charges for physics work
- Ten significant digits
- Copy button
- Runs in your browser
Frequently asked questions
How many coulombs are in one amp-hour?
Exactly 3,600. One ampere is one coulomb per second, and an hour is 3,600 seconds.
How do I convert by hand?
Multiply the amp-hours by 3,600. A 2.5 Ah battery holds 9,000 C.
What about milliamp-hours?
Divide by 1,000 first: 1 mAh is 3.6 C, so a 3,000 mAh phone battery is 10,800 C.
Is charge the same as energy?
No. Charge in coulombs says how many electrons moved. Energy in joules also depends on the voltage: joules = volts × coulombs. Use the Volts to Joules calculator for that.
Does this tell me how long a battery lasts?
Not by itself. Divide the amp-hours by the current in amps to get hours, or use the Battery Runtime Calculator.
Why would I need coulombs for a battery?
Physics and electrochemistry problems, such as how much metal is deposited in electrolysis, use coulombs.
Is my number uploaded?
No.