What is the difference between mechanical and metric horsepower?

Mechanical (imperial) horsepower is 745.7 W and is standard on US nameplates. Metric horsepower, also called PS or cheval, is 735.5 W and appears on many European and Asian motors. They differ by about 1.4 percent, so a 100 HP rating means slightly less power if it is metric.

Why is electrical input power higher than the rating?

The nameplate horsepower or kW is the mechanical power delivered at the shaft. The motor draws more electrical power because of copper, iron, and friction losses. Dividing shaft power by efficiency, for example 0.90, gives the real input draw used for wiring and breaker sizing.

How is shaft torque calculated?

Power equals torque times angular speed. In SI the tool uses T = 9.5488 × kW × 1000 / RPM for newton-metres. In imperial units the classic relation T = 5252 × HP / RPM gives pound-feet, where 5252 is 33,000 divided by 2π.

Which horsepower should I use for sizing wire?

Size conductors and overloads from the electrical input, not the shaft rating. Use the motor's full-load current from its nameplate or the NEC motor tables. This converter helps you cross-check the input kW that current implies.

Is electrical HP the same as mechanical HP?

Electrical horsepower is defined as exactly 746 W, a rounded figure used in some electrical contexts, while mechanical horsepower is 745.7 W. The difference is tiny, about 0.04 percent, and rarely matters in practice.

Motor Horsepower to kW Converter

Motor nameplates come in mechanical horsepower, metric horsepower (PS), or kilowatts depending on where the motor was made, and comparing them needs the exact conversion constants. This tool converts between all of them, derives the electrical input power from efficiency, and computes shaft torque at any speed.

How it works

Each unit maps to watts through its defining constant, then back to the others:

1 mechanical HP = 745.700 W
1 metric HP (PS) = 735.499 W
1 electrical HP  = 746.000 W

Electrical input power accounts for motor losses, and torque follows from the power-speed relationship:

input kW = shaft kW / efficiency
T (N·m)  = 9.5488 × kW × 1000 / RPM
T (lb·ft)= 5252 × HP / RPM

Example and notes

A 10 HP mechanical motor delivers 7.457 kW at the shaft. At 90 percent efficiency it draws about 7.457 / 0.90 ≈ 8.29 kW electrically. Running at 1750 RPM it produces roughly 40.7 N·m, or 30 lb·ft, of torque. Always size the supply circuit from the electrical input and the nameplate full-load current, not from the mechanical rating, because the loss component is real load on the wiring.