Engineering
Electricity kWh and utility cost calculator formula (Watts to $ bill)
Estimate energy use and the energy component of a bill from average input power, operating hours and a flat tariff.
From Watts to Kilowatt-Hours (kWh) and monthly utility cost
Energy in kWh equals average input watts times operating hours divided by 1000.
Multiply energy by a flat rate per kWh to estimate the energy charge. The example compares two assumed constant loads, not a guaranteed equipment-upgrade saving.
| Load Scenario (8 hrs/day, 30 days, $0.18/kWh) | Monthly kWh | Monthly Cost |
|---|---|---|
| 1,500 W assumed load | 360.0 kWh | $64.80 |
| 450 W assumed load | 108.0 kWh | $19.44 (Saves $45.36/mo) |
Monthly kWh and utility cost formulas
Divide Watt-hours by 1000 before multiplying by the $/kWh utility rate.
=ROUND(((A2 * B2 * C2) / 1000) * D2, 2)Monthly energy consumption in kWh
Useful for carbon-footprint tracking (kg CO2 = kWh * GridEmissionFactor).
=(A2 * B2 * C2) / 1000Inputs and interpretation
Use measured average real input power while operating, not output ratings or apparent power. Require nonnegative power and days, and hours per day from 0 to 24. Duty cycles, standby loads and variable tariffs may need separate rows. The result covers the energy charge only, excluding fixed fees, demand charges and taxes. Compare equipment at equivalent useful output, not wattage alone.
Try the example
Use the original values or change them to test your understanding.