Question 1

How are power, torque and RPM related?

Accepted Answer

Mechanical power is torque times angular velocity: P = T × ω, where ω = 2πN/60 with N in rpm. Combining them gives P = 2πNT/60. So for T = 10 N·m at N = 1500 rpm, P = 2π × 1500 × 10 / 60 = 1570.8 W ≈ 1.571 kW.

Question 2

How do I find torque from power and speed?

Accepted Answer

Rearrange the relation to T = 60P / (2πN) = 9.5493 × P / N, with P in watts and N in rpm. For example, 1500 W at 3000 rpm gives T = 9.5493 × 1500 / 3000 = 4.775 N·m.

Question 3

How do I convert watts to horsepower?

Accepted Answer

Mechanical (imperial) horsepower is P[HP] = P[W] / 745.7, and metric horsepower is P[PS] = P[W] / 735.5. So 1570.8 W is about 2.106 HP or 2.136 PS. The tool shows both alongside the result.

Question 4

Is this the motor's input electrical power?

Accepted Answer

No. This is the ideal shaft (mechanical) relation P = T × ω. The electrical input power of a motor is higher because of efficiency losses, and for AC it also involves power factor. Divide shaft power by efficiency to estimate input power.

Question 5

What units should I use?

Accepted Answer

Use SI: torque in newton-metres (N·m), speed in revolutions per minute (rpm) and power in watts (W). The 2πN/60 factor converts rpm to radians per second. The tool accepts W or kW and N·m, mN·m or kN·m and handles the conversion for you.

Power · Torque · RPMCalculator

Power · Torque · RPM
Calculator