Start only when the input source is clear
This page is for a chosen watts-and-runtime scenario. It does not decide whether a label wattage is representative of a cycling appliance, and it does not replace a kWh reading you already measured. For that decision, use the watts vs kWh guide or price a labeled period with the kWh to Cost Calculator.
The worksheet formula
Selected-period usage cost = watts x hours x quantity / 1000 x rate per kWh. Keep the inputs at full precision through the calculation and round only the displayed result.
For this formula, write the rate in currency units: 17.3 cents per kWh is 0.173 dollars per kWh, not 17.3 dollars. Convert minutes to hours by dividing by 60. Quantity assumes identical devices with the same runtime; calculate different wattages or schedules separately, then add their costs.
Check each formula step before moving on
Use this table to pause at the step where an input is missing. Move to a calculator only after watts, runtime, and rate are clear enough for the estimate you want to make.
Scroll horizontally to see all columns.
| Formula step | Input needed | Stop if... | Continue when... |
|---|---|---|---|
| Define the load | Watts, operating mode, and quantity | You only have volts, amps, or a mode label. Find wattage first, or use known kWh when you measured energy use. | You have a watt value tied to the device and mode you are estimating. |
| Runtime to kWh | Hours of use | The runtime does not match the session, day, or month you want to estimate. | You have hours that match the habit or period you are comparing. |
| kWh to cost | Rate per kWh | The number is a total bill amount, fixed charge, or unclear bill line. | You have a per-kWh rate or a rough fallback that you will label as approximate. |
| Interpret result | Usage-cost estimate | You are comparing it directly with the full bill total. | Keep fixed fees and charges excluded from the selected rate separate. Do not add per-kWh delivery charges again if the rate already includes them. |
Worked worksheet: one work-light session
This is an illustrative labeled-watts example, not a measured result. The goal is to show what must be recorded so another reader can reproduce the estimate or replace an assumption.
- Load: one portable work light, labeled 42 W in the selected mode
- Period: one 6.5-hour work session
- Rate: 0.173 per kWh in the example currency
- Excluded: standby use, other devices, fixed bill charges, taxes, and delivery adjustments
Worksheet line 1: confirm watts, mode, and quantity
The selected load is 42 W because the worksheet covers one light in that labeled mode. If several matching lights were used, quantity would be part of the load before continuing.
Worksheet line 2: convert the session into energy
42 W x 6.5 hours / 1000 = 0.273 kWh. This value belongs to one 6.5-hour session. If energy use is the only result you need, the Watts to kWh Calculator performs this conversion without the remaining worksheet.
Worksheet line 3: apply the recorded rate
0.273 kWh x 0.173 per kWh = 0.047229, which displays as about 0.05 in the same currency as the example rate. If your rate source is unclear, resolve it with the electricity rate guide before replacing 0.173.
Worksheet line 4: state what the result does and does not cover
The result estimates this light's usage cost for one documented work session. It is not a monthly pattern until the number of matching sessions is known, and it is not the full bill total. Keep the unrounded 0.047229 value for any later scaling, then round the final displayed amount.
Replace assumptions one at a time
To adapt the worksheet, first replace the wattage and operating mode, then the runtime and quantity, and finally the rate. Do not copy the sample's 6.5-hour period unless it matches the use you are estimating. For a recurring daily pattern, the Appliance Electricity Cost Calculator keeps use days separate from the one-session calculation.
Use another path when watts are not the best input
- If you do not know what the printed number represents, diagnose it with Watts vs kWh.
- If the device cycles or changes power substantially, use measured kWh for a defined interval when available.
- If you already have kWh, skip this worksheet and use the kWh to Cost Calculator.
- If the estimate is being compared with a bill total, separate appliance usage from other charges with the bill difference guide.