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Electric & Combustion Motor Torque, Power (kW/HP) & RPM Calculator

Calculate mechanical torque (N·m / lb-ft), angular velocity (rad/s), and shaft horsepower from rotational speed.

Last reviewed by the myCalculator Editorial Team

Input Parameters

kW

e.g. 15 kW (approx 20.1 HP)

RPM

Standard 4-pole 50Hz induction motor runs at ~1450 RPM; 2-pole runs at ~2900 RPM

Standard IEC / NEMA continuous overload capacity factor (typically 1.0 to 1.25)

Calculation Results

Rated Output Torque
98.79 N·m (72.86 lb-ft)
Shaft Power (kW / HP)
15 kW (20.12 HP)
Rotational Speed
1,450 RPM (151.8 rad/s)
Service Factor Rated Torque
113.6 N·m (SF = 1.15)
Linear Work per Revolution
620.7 Joules / rev
Summary: A 15 kW (20.1 HP) motor spinning at 1450 RPM produces 98.79 N·m (72.9 lb-ft) of continuous torque at an angular velocity of 151.8 rad/s.

Visual Growth Breakdown

Step-by-Step Calculation Solution
1.Angular Velocity (ω) = 2 × π × N ÷ 60 = 2 × π × 1450 ÷ 60 = 151.844 rad/s
2.Torque (N·m) = (Power in Watts) ÷ ω = (15000 W) ÷ 151.844 = 98.79 N·m
3.Imperial Torque (lb-ft) = (HP × 5252) ÷ RPM = (20.12 × 5252) ÷ 1450 = 72.86 lb-ft
4.Shaft Power in HP = 15 kW × 1.34102 = 20.12 HP

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Formula & How Electric & Combustion Motor Torque, Power (kW/HP) & RPM Calculator Works

Mathematical Formula
Torque (N·m) = (Power in Watts) ÷ (2 × π × RPM ÷ 60) = (kW × 9548.8) ÷ RPM | HP = kW × 1.341

Shaft torque is power divided by angular speed. In kilowatts and RPM the shortcut is torque (N·m) = kW × 9,548.8 ÷ RPM. A 15 kW motor running at 1,450 RPM delivers 15 × 9,548.8 ÷ 1,450 = about 98.8 N·m, and 15 kW is about 20.1 hp. A service factor allows for demanding loads: applying 1.15 gives a design power of 17.25 kW and a design torque of about 113.6 N·m. Torque rises as speed falls for the same power, which is why a gearbox that slows the shaft multiplies the available torque. Always check the motor nameplate and the driven equipment's starting torque requirement.

How to Calculate Electric & Combustion Motor Torque, Power (kW/HP) & RPM Calculator (Step-by-Step)
  1. Enter Shaft Power Rating (kW) (kW): Input your target parameter value.
  2. Enter Rotational Speed (RPM) (RPM): Input your target parameter value.
  3. Enter Motor Service Factor (SF): Input your target parameter value.
  4. Apply Formula: Calculate using Torque (N·m) = (Power in Watts) ÷ (2 × π × RPM ÷ 60) = (kW × 9548.8) ÷ RPM | HP = kW × 1.341.
  5. Review Results: View exact computed answers, metrics, and worked mathematical proofs.
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MyCalculator.com.au. (2026). Electric & Combustion Motor Torque, Power (kW/HP) & RPM Calculator. Retrieved October 24, 2026, from https://www.mycalculator.com.au/calculators/engineering/motor-torque-rpm

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MyCalculator.com.au. (2026) 'Electric & Combustion Motor Torque, Power (kW/HP) & RPM Calculator'. Available at: https://www.mycalculator.com.au/calculators/engineering/motor-torque-rpm (Accessed: 24 October 2026).

Frequently Asked Questions (FAQs)

What is the relationship between motor RPM and torque?

At a constant power rating, torque is inversely proportional to rotational speed (RPM). Reducing motor speed via a gearbox increases output torque proportionally.

How do you convert kilowatts (kW) to horsepower (HP)?

1 metric Kilowatt equals approximately 1.34102 mechanical Horsepower ($1 \text{ HP} = 0.7457 \text{ kW}$).

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Calculations and mathematical logic on this page are grounded in published statutory rules, regulatory standards, and official government data published by the following bodies:

Standards AustraliaOfficial Standard
Peak Non-Government Standards Organization

Australian Standards including AS/NZS 3000 (Wiring Rules), AS 3600 (Concrete Structures), and AS 4100 (Steel Structures).

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