How to calculate the capacity of a lithium ion battery

The capacity of a lithium battery may be expressed as energy stored (Wh) or ampere hours (Ah).

This article explains the difference between ampere hours (Ah) and watt hours (Wh), how to calculate and convert from one to the other by providing a worked calculation or by simply using our online calculator!

Lithium battery capacity in ampere hours (Ah), is a rough indication of how many hours the battery can provide a specified amount of current(A). For example a 4 Ahr battery can provide approximately 1 A for 4 hours or 2 A for 2 hours before it is depleted.

Watt hours (Wh), on the other hand gives an indication of how long a battery can provide a certain amount of energy (w) when to an appliance. Laptop batteries usually have their capacity in Wh or mAh.  For example:5000 mAh/ 55Wh for a 10.8V laptop battery.

Laptop battery

10.8V, 55Wh battery equivalent to 5,000  mAh

To work out how to convert from Wh to Ah, you may use the calculator below or follow the worked example.

Worked example

To calculate the Watt Hours (Wh) of a lithium battery, simply multiply the battery voltage (volts) by the battery capacity in Ah.

For example:
A DELL laptop battery with a voltage of 14.8V and a battery capacity of 2600 mAh has an equivalent capacity of 14.8 x 2600/1000= 38.48Wh approx 40Wh. To calculate the Ah (Ah) of a lithium battery, simply divide the battery capacity in Wh by the battery voltage

For example, a laptop battery with a voltage of 11.1V and a capacity of 97 Wh has an equivalent capacity of 8,738 mAh or approx. 8,700 mAh.

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