100 HP motor electricity cost calculator
Convert motor horsepower into estimated electrical input, monthly kWh, and energy cost. Unlike a simple horsepower conversion, this calculator includes motor efficiency and average load.
100 HP motor electricity cost
Adjust the nameplate horsepower, efficiency, average load, operating schedule, and electricity rate. The default is an illustrative 100-horsepower motor running at 75% load.
How much does a 100 HP motor cost to operate?
A 100 HP motor operating at 75% average load and 92% efficiency draws an estimated 60.8 kW. At 10 hours per day, 22 days per month, and $0.12/kWh, that equals approximately 13,378 kWh and $1,605 per month in energy charges. At full load, the same motor would draw about 81.1 kW and cost roughly $9.73 per operating hour at that energy price.
The calculation
The U.S. Department of Energy uses the same core relationship in its motor-system guidance: horsepower, the 0.746 kW/hp conversion, operating hours, load factor, motor efficiency, and electricity price. The formula is a screening estimate. A true three-phase power measurement from a suitable meter is preferable when a purchasing or retrofit decision depends on the result.
Why 74.6 kW is not the full-load electrical input
Multiplying 100 HP by 0.746 gives 74.6 kW of mechanical output. Because a motor loses some energy as heat and other losses, its electrical input must be higher than its shaft output. Dividing by 92% efficiency gives approximately 81.1 kW at full load.
The nameplate efficiency applies under specified test conditions, and efficiency can change at part load. For a careful estimate, use measured input power or manufacturer performance data at the actual operating point.
Energy charge versus demand charge
| Bill component | Motor effect | Calculation |
|---|---|---|
| Energy charge | Accumulates whenever the motor runs | Input kW × hours × $/kWh |
| Demand charge | Depends on whether the motor overlaps the facility peak | Incremental billed kW × $/kW |
| Power-factor charge | May apply under some commercial or industrial tariffs | Utility-specific tariff method |
Starting current is important for electrical design and protection, but a brief start does not automatically equal the billed demand. The result depends on the utility’s demand interval, metering, and tariff rules.
When a more detailed motor study is worthwhile
- The motor operates for thousands of hours per year.
- Its actual load is uncertain or changes substantially.
- A pump, fan, or compressor uses throttling or bypass control.
- The motor regularly overlaps the facility’s billed peak.
- You are comparing a replacement, rewind, premium-efficiency motor, or variable-frequency drive.
DOE recommends a motor-system approach rather than evaluating only the motor. Pumps, fans, compressed-air systems, controls, process requirements, maintenance, and right-sizing can determine whether a proposed change produces real savings.
Frequently asked questions
How many kW does a 100 HP motor use?
One hundred mechanical horsepower equals 74.6 kW of output at full load. Electrical input is higher because the motor is not 100% efficient. At 92% efficiency, full-load input is approximately 81.1 kW.
How much does a 100 HP motor cost to run per hour?
At full load, 92% efficiency, and $0.12/kWh, the energy charge is approximately $9.73 per hour. The actual cost changes with measured load, efficiency, tariff price, and demand charges.
Does power factor change the kWh formula?
If horsepower, load, and motor efficiency are known, the simplified input-kW estimate does not require a separate power-factor term. Power factor is needed when estimating three-phase real power from volts and amps.