What is an amp-hours to watt-hours calculator?
An amp-hours to watt-hours calculator converts a battery’s charge capacity into the amount of energy it can store. Amp-hours (Ah) measure charge — how much current a battery can supply for how long — but two batteries with the same amp-hour rating can hold very different amounts of energy depending on their voltage. Watt-hours (Wh) fold the voltage in, giving a single figure that lets you compare batteries of different voltages on an equal footing.
This is why energy ratings, capacity labels, and shipping limits for lithium batteries are almost always quoted in watt-hours rather than amp-hours.
How does it work?
Energy equals charge multiplied by voltage. Multiply the capacity in amp-hours by the nominal voltage to get the stored energy in watt-hours:
Here is the energy in watt-hours, is the charge in amp-hours, and is the nominal voltage in volts.
How to use
- Enter the battery’s charge capacity in amp-hours (Ah).
- Enter the voltage of the battery in volts (V).
- Read the stored energy in watt-hours. The result appears automatically once both fields are filled.
Worked examples
A 12-volt battery rated at 8 amp-hours stores:
A smaller 12-volt pack rated at 5 amp-hours holds:
The same arithmetic scales to any voltage: a 5 Ah cell at 3.7 V stores 18.5 Wh, while a 100 Ah deep-cycle battery at 12 V stores 1200 Wh, or 1.2 kWh.
Practical notes
Use the nominal voltage printed on the battery rather than its momentary reading, which rises when fully charged and sags under load. The result is the theoretical energy capacity; usable energy is lower because most chemistries should not be drained completely, and conversion losses reduce what reaches the load.
To work in the opposite direction with power and time, the kWh to watts calculator turns energy and run time into an average power draw. If you need current instead of energy, the amps to watts calculator converts between current and power at a given voltage.