Calculator
Formula Used
Electric shaft HP: input kW × motor efficiency × drive efficiency × load ÷ 0.745699872.
Rated electric shaft HP: rated HP × load percentage.
Gas shaft HP: gas rated HP × gas load percentage.
Gas fuel kW: gas shaft HP × 0.745699872 ÷ gas engine efficiency.
Fuel units per hour: gas fuel kW ÷ fuel energy per unit.
Torque: HP × 5252 ÷ RPM for lb-ft.
Monthly savings: gas monthly cost − electric monthly cost.
Payback: conversion cost ÷ monthly savings.
How to Use This Calculator
- Select whether electric power is entered as input kW or rated HP.
- Enter electric efficiency, drive efficiency, load, RPM, and electricity price.
- Enter gas rated HP, engine efficiency, load, RPM, fuel energy, and fuel price.
- Add daily run hours, work days, and carbon factors if needed.
- Press Calculate to compare horsepower, torque, cost, savings, and payback.
- Use CSV or PDF buttons to download the current result.
Example Data Table
| Scenario | Electric Input | Electric Efficiency | Gas HP | Gas Efficiency | Run Hours | Use Case |
|---|---|---|---|---|---|---|
| Small pump | 3.0 kW | 90% | 6.5 HP | 22% | 4/day | Irrigation transfer |
| Shop compressor | 7.5 kW | 92% | 13 HP | 25% | 6/day | Air tools |
| Fan drive | 11.0 kW | 94% | 20 HP | 28% | 10/day | Ventilation |
Electric HP and Gas HP Comparison
Electric motors and gas engines do not feel the same at work. An electric motor can deliver strong torque from low speed. A gas engine usually needs higher rpm to reach rated horsepower. This calculator helps compare both power sources in a practical way.
Why the Comparison Matters
Nameplate horsepower is only the starting point. Useful output depends on efficiency, load factor, duty cycle, fuel cost, electricity price, runtime, and losses. A gas engine may advertise more horsepower, yet spend more energy through heat and friction. An electric motor may use less input energy for the same shaft work. This difference can change operating cost and equipment size.
What the Calculator Estimates
The tool converts electric power to mechanical horsepower. It also estimates equivalent gas horsepower at the shaft. It compares hourly energy use, energy cost, daily cost, monthly cost, torque, carbon output, and payback. You can enter motor efficiency, engine efficiency, load percentage, run hours, fuel price, and utility price. The result shows whether the electric setup or gas setup is more economical for the same job.
Practical Use Cases
Use it for pumps, compressors, shop tools, generators, carts, mowers, fans, winches, and small industrial machines. It is useful when replacing a gas engine with an electric motor. It also helps compare operating budgets before buying equipment. For mobile work, include battery capacity and charging losses. For fixed work, focus on grid power cost and runtime.
Reading the Results
A lower hourly cost means cheaper operation. Higher shaft horsepower means more useful output at the machine. Torque depends on horsepower and rpm. A motor with lower horsepower may still feel stronger at low rpm because it delivers torque earlier. Always check starting load, surge load, cooling needs, duty rating, and manufacturer limits before final selection.
Better Decisions
This calculator is an estimate, not a safety approval. Real performance depends on altitude, temperature, fuel quality, wiring, gearing, belts, batteries, and maintenance. Use conservative values when data is unknown. Then compare several scenarios. Small changes in efficiency or runtime can create large cost differences over a month. Keep records from repeated jobs. They improve future estimates and make replacement choices easier for owners and technicians.
FAQs
1. What is electric HP?
Electric HP is the mechanical horsepower produced by an electric motor shaft. It depends on input power, motor efficiency, drive efficiency, and actual load. It is not always the same as electrical input power.
2. What is gas HP?
Gas HP is the rated mechanical output of a gasoline engine. Real output changes with throttle, load, rpm, altitude, temperature, maintenance, and fuel quality. The calculator uses rated HP and load percentage.
3. Why can a smaller electric motor replace a gas engine?
Electric motors often deliver strong torque at low speed. Gas engines usually need higher rpm to reach peak output. Because of this, a lower rated electric motor may perform well in some applications.
4. Does horsepower alone decide performance?
No. Torque, rpm, gearing, duty cycle, cooling, starting load, and efficiency also matter. Two machines with the same HP can feel different in real work.
5. What fuel energy value should I use?
Use the energy content for your fuel unit. For gasoline, many estimates use about 33.7 kWh per gallon. You can change the value for diesel, propane, or local fuel data.
6. What does load percentage mean?
Load percentage is the share of rated capacity being used. An engine rated at 10 HP running at 70% load delivers about 7 HP at the shaft.
7. Why is payback not shown sometimes?
Payback needs positive monthly savings. If electric operation is not cheaper with your values, the tool shows no payback from entered costs.
8. Can this calculator choose a motor size?
It can guide early sizing. Final selection should include starting torque, surge load, duty rating, enclosure, voltage, gear ratio, safety factor, and manufacturer recommendations.