How to Convert Between Coulombs, Amp-Hours, and mAh

A battery’s rated capacity is printed in mAh, a physics problem expresses charge in coulombs, and a larger battery pack’s spec sheet lists Ah — three units for the same underlying quantity, electric charge, but scaled and defined differently enough that converting between them isn’t just moving a decimal point the same way every time. Coulombs and amp-hours in particular aren’t related by a simple factor of a thousand the way milli- and base units usually are — the relationship between them involves the number of seconds in an hour, which is a much less obvious multiplier to keep in your head.

Getting this right matters for anything comparing a battery’s rated capacity against a device’s actual current draw, or converting between a physics-context charge figure and a practical battery-capacity one.

What converting between coulombs, Ah, and mAh actually involves

The coulomb is the base SI unit of electric charge, defined directly in terms of current and time — one coulomb is the charge transferred by one amp of current flowing for one second. Amp-hours, by contrast, is a more practically-scaled unit used for battery capacity: one amp-hour is one amp of current sustained for one hour, which works out to 3,600 coulombs, since there are 3,600 seconds in an hour. Milliamp-hours is simply a thousandth of an amp-hour, following the more familiar milli-scaling. This means converting between coulombs and amp-hours involves that less-obvious factor of 3,600, not a round factor of a thousand, which is exactly where a mental conversion attempt tends to go wrong — people often assume the relationship is a clean order-of-magnitude shift when it actually isn’t.

Getting the conversion right matters practically for anything comparing a battery’s rated capacity, typically in mAh, against a calculated charge requirement that might be expressed in coulombs from a physics-based calculation.

Why people get stuck here

• Coulombs and amp-hours aren’t related by a simple factor of a thousand. The actual relationship involves 3,600 — the number of seconds in an hour — which is a far less intuitive multiplier than the round-number scaling most unit conversions follow.
• mAh and Ah do follow the familiar thousand-fold milli-scaling, which can create a false sense that all these units scale the same way. Assuming coulombs fit the same simple pattern as mAh and Ah leads directly to an incorrect conversion.
• Battery specs and physics calculations default to different units. A device’s rated capacity in mAh and a charge requirement calculated in coulombs from a physics problem need to be converted to the same unit before they can be meaningfully compared.
• Manual conversion involving the 3,600 factor is easy to get wrong under time pressure. Multiplying or dividing by 3,600 by hand, especially combined with a milli-scale adjustment, is where calculation slips tend to happen.

What a good charge converter looks like

Applies the correct 3,600-second relationship between coulombs and Ah

Getting this specific, less-intuitive factor right is what distinguishes an accurate conversion from one that mistakenly assumes a simple thousand-fold scale.

Handles the mAh-to-Ah milli-scaling correctly alongside it

Combining both the coulomb-to-Ah relationship and the standard milli-scaling accurately in one calculation avoids compounding errors.

Converts instantly between all three units

Fast, accurate conversion between coulombs, Ah, and mAh removes the need to manually chain two different scaling relationships together.

Common mistakes to avoid

• Assuming coulombs and amp-hours are related by a simple factor of a thousand rather than the actual 3,600-second relationship.
• Comparing a battery’s mAh rating against a coulomb-based charge calculation without converting one to match the other first.
• Making an arithmetic mistake when manually multiplying or dividing by 3,600 during a coulomb-to-Ah conversion.
• Overlooking the milli-scale adjustment between mAh and Ah when the conversion also involves coulombs.

How to do it with Charge Converter

Online Tool Store’s Charge Converter takes an electric charge value in coulombs, amp-hours, or milliamp-hours and converts it to every other unit instantly, entirely in your browser.

1. Enter your charge value and its unit.
2. Get it converted to every other unit instantly.
3. Use the accurate figure to compare against a battery spec or calculation.
4. Apply the correctly converted value to your analysis or design decision.

Because the specific 3,600-second relationship between coulombs and amp-hours is applied correctly alongside the standard milli-scaling, you get an accurate conversion without manually chaining two different factors together.

Frequently asked questions

Why isn’t the conversion between coulombs and amp-hours a round number?

Because an amp-hour is defined as one amp sustained for one hour, and there are 3,600 seconds in an hour — the conversion factor comes directly from that time relationship, not a simple decimal scale.

Is converting between mAh and Ah the same as converting between coulombs and Ah?

No — mAh to Ah follows the familiar thousand-fold milli-scaling, while coulombs to Ah involves the less intuitive 3,600-second factor; the two conversions use genuinely different relationships.

Why would I need to convert a battery’s mAh rating to coulombs?

This comes up when comparing a battery’s practical capacity rating against a charge requirement calculated from a physics-based formula, which is typically expressed in coulombs rather than amp-hours.

Final thought

Coulombs and amp-hours look like they should convert with a simple round factor, but the real relationship runs through the number of seconds in an hour. Convert it correctly, and compare battery capacity against any charge calculation with confidence.

Try the free Charge Converter