About the Electric Charge Converter
Electric charge shows up in two very different unit families: coulombs and millicoulombs from physics and electrical engineering, and amp-hours and milliamp-hours from battery and consumer electronics specs. This calculator converts between all four so a charge value from a physics problem or a battery datasheet can be expressed in whichever unit you need.
How It Works
Enter a charge value and select the unit it's currently in and the unit to convert it to. The calculator converts your input into coulombs using each unit's fixed multiplier, then divides that coulomb value by the target unit's multiplier to produce the converted result. A table below the main result also repeats the same conversion for input values of 1, 5, 10, 25, 50, and 100, making it easy to scan how a range of charge or capacity readings line up in the target unit.
Formula & Methodology
The amp-hour and milliamp-hour factors come directly from the definition of an amp: one amp is one coulomb of charge per second, so one amp-hour is one amp sustained for 3600 seconds, or 3600 coulombs. A milliamp-hour is a thousandth of that, giving a factor of 3.6 coulombs. Converting 3000 mAh to coulombs, for example, multiplies 3000 by 3.6 to get 10,800 coulombs of stored charge.
Examples
A 3000 mAh phone battery
Converting 3000 milliamp-hours to amp-hours gives 3 Ah, and to coulombs gives 10,800 C, the total charge the battery can deliver.
One amp-hour in coulombs
Converting 1 amp-hour directly to coulombs gives exactly 3600 C, matching the definition of an amp-hour as one amp of current sustained for one hour.
Advantages
- Bridges the physics unit, coulombs, with the consumer electronics unit, amp-hours, that appears on every phone, laptop, and power bank battery label.
- Handles the 3600x scale difference between coulombs and amp-hours automatically, a conversion that's easy to get an order of magnitude wrong by hand.
- Includes a comparison table across multiple input values, useful for scanning how a range of battery capacities translate into coulombs at a glance.
Common Mistakes
- Assuming amp-hours measure energy the same way watt-hours do, when amp-hours measure charge only and say nothing about voltage.
- Mixing up milliamp-hours and amp-hours, a factor-of-1000 error that's easy to make when copying a spec from a datasheet.
- Forgetting that a device's actual runtime also depends on its current draw, not just the battery's charge rating, so charge alone doesn't predict usage time.
Edge Cases to Watch For
- Coulombs is used as the internal base unit for every conversion, so a conversion between two derived units, like milliamp-hours to amp-hours, still passes through a coulombs intermediate step even though it isn't shown separately.
- The amp-hour and milliamp-hour units describe charge capacity only. They say nothing about the voltage a battery operates at, so this converter cannot be used on its own to compare the actual stored energy of two batteries rated at different voltages.
- Results display with up to 6 significant figures of precision, which can render very small millicoulomb-to-amp-hour conversions in a long decimal form, since one amp-hour is 3.6 million times larger than one millicoulomb.
Common Use Cases
- Electronics hobbyists and engineers converting battery datasheet specs given in mAh into coulombs for a physics or circuit calculation.
- Students working through electricity and magnetism problems that mix coulombs with amp-based battery specs.
- Anyone comparing battery capacities listed in different unit conventions, such as a power bank in mAh against a lab power supply spec in coulombs.