Watt-Hours Calculator
Convert battery amp-hours and voltage to watt-hours.
Results update as you type.
How it works
Watt-hours measure the actual energy a battery stores, and this calculator converts amp-hours and voltage into watt-hours. You enter the battery's capacity in amp-hours and its voltage, and it returns the energy in watt-hours and kilowatt-hours. This conversion matters because amp-hours alone, the way many batteries are rated, measure only electric charge, not energy, and cannot be compared fairly across batteries of different voltages. A 100 amp-hour battery at 12 volts and a 50 amp-hour battery at 24 volts hold the same energy, 1,200 watt-hours, even though their amp-hour ratings differ. Multiplying amp-hours by voltage gives watt-hours because power in watts is voltage times current, so charge times voltage is energy over time, which is energy. Watt-hours are the standard energy unit for comparing batteries, sizing solar and off-grid systems, estimating device runtime alongside power consumption, and understanding electric vehicle and power-bank capacity. Dividing by a thousand gives kilowatt-hours, the unit utilities use for electricity billing, so this also links battery capacity to grid energy. Knowing watt-hours lets you calculate how long a battery can supply a given power draw: runtime in hours is watt-hours divided by the load in watts. Enter the amp-hours and voltage to compute the watt-hours.
Wh = amp-hours × voltage
Watt-hours, a measure of energy, equal the charge capacity in amp-hours multiplied by the voltage. Amp-hours alone measure charge, but multiplying by voltage converts it to energy, since power is voltage times current. Dividing by 1,000 gives kilowatt-hours. This lets you compare batteries of different voltages on a common energy basis.
Source:Electrical energy
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter capacity and voltage.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Energy updates instantly as you type — no button to press.
Frequently asked questions
How do you convert amp-hours to watt-hours?
Multiply the capacity in amp-hours by the battery voltage. A 100 amp-hour battery at 12 volts stores 1,200 watt-hours. This works because energy equals electric charge times voltage. The calculator returns the result in both watt-hours and kilowatt-hours as soon as you enter the amp-hours and the voltage.
Why not just use amp-hours?
Amp-hours measure electric charge, not energy, so they cannot be compared across batteries of different voltages. A 100 amp-hour 12-volt battery and a 100 amp-hour 24-volt battery hold very different amounts of energy. Watt-hours, which fold in voltage, give a true energy figure that allows a fair comparison between any batteries.
What are watt-hours used for?
Watt-hours are the standard measure of stored energy, used to size solar and off-grid battery banks, rate power banks and electric vehicles, and estimate how long a battery can run a device of known power draw. Dividing watt-hours by a load in watts gives the runtime in hours, a common practical calculation.
How do watt-hours relate to kilowatt-hours?
A kilowatt-hour is 1,000 watt-hours, so you divide watt-hours by a thousand to convert. Kilowatt-hours are the unit electric utilities use for billing, so expressing battery capacity in kilowatt-hours connects it directly to how much grid electricity it could store or replace, useful for home energy and solar planning.
How do I find runtime from watt-hours?
Divide the battery's watt-hours by the device's power consumption in watts. A 1,200 watt-hour battery running a 100-watt device lasts about 12 hours before losses. This is a useful companion calculation: watt-hours give the total energy, and dividing by the load's power gives how long that energy lasts.