Enter the energy consumption and power rating into the calculator to determine the time it takes for the energy to be consumed. This calculator can also evaluate any of the variables given the others are known.

Watts To Time Calculator

Enter any 2 values to calculate the missing variable

Watts To Time Formula

The following formula is used to calculate the time it takes for a certain amount of energy to be consumed.

T = E / P

Variables:

  • T is the time (in hours when units are consistent, such as Wh with W, or kWh with kW)
  • E is the energy used (watt-hours, Wh, or kilowatt-hours, kWh)
  • P is the power (watts, W, or kilowatts, kW)

To calculate the time, divide the energy used by the power after converting units so they match (for example, convert kWh to Wh if your power is in W, or convert W to kW if your energy is in kWh). This will give you the duration (time) in hours, which can then be converted to minutes or seconds if needed. This can be useful in estimating the operating cost or energy efficiency of an appliance or system.

Watts to Time Conversion Table (Assumes Energy E = 1.00 kWh = 1000 Wh)
Power (W) Time (hours) Time (minutes) Time (seconds)
5200.00012000720000
10100.0006000360000
1566.6674000240000
2050.0003000180000
2540.0002400144000
3033.3332000120000
4025.000150090000
5020.000120072000
6016.667100060000
7513.33380048000
10010.00060036000
1506.66740024000
2005.00030018000
2504.00024014400
3003.33320012000
4002.5001509000
5002.0001207200
7501.333804800
10001.000603600
20000.500301800
*Assumes fixed energy E = 1.00 kWh (1000 Wh). Time t = E ÷ P. Hours rounded to 3 decimals.

What is Watts To Time?

Watts to Time is a calculation used to determine how long it takes to use a given amount of energy (for example, in watt-hours (Wh) or kilowatt-hours (kWh)) at a given power draw (in watts (W) or kilowatts (kW)). The time is calculated by dividing energy by power. For the result to be in hours, the units must be consistent (Wh with W, or kWh with kW); otherwise, convert units first (for example, 1 kWh = 1000 Wh).

How to Calculate Watts To Time?

The following steps outline how to calculate the Watts To Time using the formula T = E / P.


  1. First, determine the energy used (E) in watt-hours (Wh) or kilowatt-hours (kWh).
  2. Next, determine the power (P) in watts (W) or kilowatts (kW).
  3. Convert units so they are consistent (Wh with W, or kWh with kW).
  4. Calculate the time (T) using T = E / P. With consistent units, T will be in hours.
  5. After calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

energy consumption (E) = 500 watt-hours

power rating (P) = 100 watts