Watt Hour (Wh) Calculator
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Understanding Watt Hours: The Ultimate Guide
Whether you are calculating the runtime of a portable power station, sizing a solar battery, or trying to understand your electric bill, knowing how to calculate Watt Hours (Wh) is an essential skill. Watt Hours measure the total amount of energy used or stored over a specific period of time.
What is a Watt Hour (Wh)?
A Watt Hour is a unit of energy equivalent to one watt (1W) of power expended for one hour (1h) of time. Unlike "Watts," which measure instantaneous power (like a speedometer measures speed), "Watt Hours" measure total energy consumed (like an odometer measures distance).
The Watt Hour Formulas
Depending on the information you have available, there are two primary ways to calculate Watt Hours:
1. Using Power and Time
If you know the wattage of your device, use this simple formula:
Watt Hours (Wh) = Watts × Hours
2. Using Voltage and Amperage
In many battery applications, you only know the Voltage (V) and the Amp-hours (Ah) or Amps (A). Use this variation:
Watt Hours (Wh) = Volts × Amps × Hours
Practical Examples
| Device | Specifications | Time | Total Watt Hours |
|---|---|---|---|
| LED Light Bulb | 10 Watts | 5 Hours | 50 Wh |
| Laptop | 65 Watts | 3 Hours | 195 Wh |
| 12V Battery | 12V @ 10 Amps | 2 Hours | 240 Wh |
| Space Heater | 1500 Watts | 1 Hour | 1500 Wh (1.5 kWh) |
How to Convert Wh to kWh
Utility companies usually bill in Kilowatt Hours (kWh). Since "kilo" means one thousand, the conversion is simple:
- To get kWh: Divide Watt Hours by 1,000.
- Example: 2,500 Wh / 1,000 = 2.5 kWh.
Why Calculating Wh Matters
Calculating Wh is critical for anyone building a DIY solar setup or choosing a backup power supply. For example, if you have a 500Wh portable power station and you want to run a 50W CPAP machine, you can estimate the runtime by dividing the capacity by the load: 500Wh / 50W = 10 hours of runtime.