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Electric charge (Q) is fundamentally measured in coulombs (C), the SI unit, defined as the charge moved by 1 ampere of current flowing for 1 second (Q=I×t). But battery capacity is almost always quoted in ampere-hours (Ah) or milliampere-hours (mAh) instead — charge moved by a current over an hour, not a second, since batteries typically discharge over hours, not seconds. Since 1 hour=3600 seconds, the exact conversion is 1 Ah = 3600 C.
| Unit | Symbol | Value in Coulombs |
|---|---|---|
| Coulomb | C | 1 |
| Milliampere-hour | mAh | 3.6 |
| Ampere-hour | Ah | 3600 |
Divide by 1000: e.g. 5000 mAh = 5 Ah.
Multiply by 3600: e.g. 2 Ah = 7200 C, since 1 hour = 3600 seconds and charge = current × time.
Batteries discharge over hours rather than seconds, so ampere-hours (charge delivered over an hour at a given current) is a far more practically-sized and intuitive unit for battery specifications than the SI coulomb.
1 Ah = 3600 C exactly, derived directly from Q=I×t with I=1 ampere and t=1 hour=3600 seconds — this is an exact definitional conversion, not an approximation.
For the same device and discharge conditions, yes — higher mAh means more stored charge and typically longer runtime, but actual runtime also depends on the device's current draw, battery voltage, and discharge efficiency, not mAh alone.
Multiply Ah by the battery's voltage to get watt-hours, then divide by 1000 for kWh: e.g. a 100 Ah, 12 V battery = 100×12=1200 Wh = 1.2 kWh — see the Battery Capacity calculator for this conversion.
It is the fundamental definition of electric charge: charge (Q, in coulombs) equals current (I, in amperes) multiplied by time (t, in seconds). Ampere-hours simply use hours instead of seconds for the time unit, which is why the 3600 conversion factor appears.
Rarely directly — coulombs are more common in physics calculations, capacitor charge (Q=CV), and electrochemistry, while everyday consumer specifications (batteries, chargers) almost always use Ah or mAh instead.
Most modern smartphones use batteries in the 3000-5000 mAh range, equivalent to roughly 10,800-18,000 coulombs.
Yes — the unit conversion itself is identical regardless of whether the charge is flowing into (charging) or out of (discharging) a battery; only the direction of current flow differs, not the unit relationship.
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