Watt Hours
Calculate energy in watt-hours from amp-hours and voltage or from power and time. Free online watt-hour calculator with interactive charts for battery capacity and energy analysis.
About This Calculator
The Watt Hours Calculator computes electrical energy in watt-hours (Wh) using two methods: from amp-hours and voltage (Ah × V), or from power and time (W × h). This tool is essential for battery capacity analysis, energy consumption tracking, and comparing batteries across different voltages. Students, engineers, electricians, and renewable energy enthusiasts use it to size batteries for solar systems, UPS backups, and portable power stations.
The fundamental formula for watt-hours is Wh = Ah × V when working with battery specifications. For example, a 12V battery rated at 100Ah delivers 1200 Wh of energy. Alternatively, when measuring device consumption, use Wh = W × h — a 60W light bulb running for 5 hours consumes 300 Wh. The calculator also converts results to joules (1 Wh = 3600 J) and kilowatt-hours (1 kWh = 1000 Wh) for utility billing comparisons.
Regional Notes
India: Electricity bills use kWh units. Battery backup systems for inverters typically range from 100Ah to 200Ah at 12V. Solar installations use watt-hours to size battery banks.
United States: Utility bills measure consumption in kWh. Deep-cycle batteries for RVs and solar are rated in amp-hours at 12V. Laptop and power bank capacities are specified in watt-hours for air travel compliance.
United Kingdom: Energy bills use kWh (often called "units"). Car battery capacities are typically 40-100Ah at 12V. Portable power stations specify capacity in watt-hours for camping and off-grid use.
Frequently Asked Questions
What is a watt-hour?
A watt-hour (Wh) is a unit of energy equal to one watt of power sustained for one hour. It is commonly used to measure battery capacity and electrical energy consumption. One watt-hour equals 3600 joules.
How do I calculate watt-hours from amp-hours?
To calculate watt-hours from amp-hours, multiply the battery voltage by the charge in amp-hours using the formula Wh = Ah × V. For example, a 12V battery with 50Ah capacity delivers 600 watt-hours of energy.
How do I calculate watt-hours from power and time?
To calculate watt-hours from power and time, multiply the power in watts by the time in hours using the formula Wh = W × h. For instance, a 100W device running for 5 hours consumes 500 watt-hours of energy.
What is the difference between watt-hours and amp-hours?
Amp-hours (Ah) measure electric charge capacity, while watt-hours (Wh) measure total energy. Watt-hours account for both the charge capacity and voltage, making them a better metric for comparing batteries with different voltages.
How many joules are in a watt-hour?
One watt-hour equals 3600 joules. This conversion is based on the fact that 1 watt equals 1 joule per second, and there are 3600 seconds in one hour (1 Wh = 1 W × 3600 s = 3600 J).
How do I convert watt-hours to kilowatt-hours?
To convert watt-hours to kilowatt-hours, divide by 1000. For example, 5000 watt-hours equals 5 kilowatt-hours (kWh). Kilowatt-hours are the standard unit used by electricity utilities for billing.
What is a typical battery capacity in watt-hours?
Common battery capacities vary widely: smartphone batteries range from 10-20 Wh, laptop batteries from 30-100 Wh, power banks from 20-100 Wh, car batteries around 600-1200 Wh, and home backup batteries from 5000-15000 Wh.
Why should I use watt-hours instead of amp-hours for battery comparison?
Watt-hours provide a more accurate comparison because they incorporate voltage. Two batteries may have the same amp-hour rating but different voltages, resulting in different total energy capacities. Always use watt-hours when comparing batteries across different voltages.