About

Engineers often face the challenge of sizing motors for specific loads while navigating a mix of Imperial and Metric units. A conveyor system might be specified in Newton-Meters while the available motor catalog lists output in Horsepower. Miscalculations here lead to stalled machinery or expensive oversizing. This tool computes output torque based on power and rotational speed variables.

The calculator incorporates an efficiency factor to distinguish between theoretical electrical power input and actual mechanical shaft output. It handles unit conversions internally to prevent the common scaling errors associated with manual factor application (such as the 5252 constant). This utility is designed for mechanical designers, electrical engineers, and automation specialists requiring precise shaft torque data.

Formulas

The fundamental relationship between power, torque, and angular velocity is derived from rotational mechanics logic.

Standard SI Formula:

P = τ × ω

Where P is Power in Watts, τ is Torque in Nm, and ω is Angular Velocity in rad/s.

Engineering Formulas (Imperial & Metric):

When using Horsepower and RPM, the formula requires a unit conversion constant derived from 330002π.

{

T (lb-ft) = 5252 × HPRPMT (Nm) = 9550 × kWRPM

Accounting for Efficiency:

Mechanical output torque is always lower than electrical input implies due to thermal and friction losses.

T_real = T_ideal × η100

Reference Data

Motor Standard	Frame Size	Ref. Speed (RPM)	Power (HP)	Approx. Torque (lb-ft)	Approx. Torque (Nm)
NEMA	42	1725	0.06	0.18	0.24
NEMA	48	1725	0.25	0.76	1.03
NEMA	56	1725	0.50	1.52	2.06
NEMA	56C	1725	1.00	3.04	4.12
NEMA	143T	1750	1.50	4.50	6.10
NEMA	145T	1750	2.00	6.00	8.13
NEMA	182T	1750	3.00	9.00	12.20
NEMA	184T	1750	5.00	15.00	20.34
NEMA	213T	1750	7.50	22.50	30.51
NEMA	215T	1750	10.00	30.00	40.67
IEC	63	1400	0.24	0.90	1.22
IEC	71	1400	0.50	1.87	2.54
IEC	80	1400	1.00	3.75	5.08
IEC	90L	1400	2.00	7.50	10.17
IEC	100L	1400	4.00	15.00	20.34

Frequently Asked Questions

The number 5252 is a rounded conversion factor. One Horsepower equals 33,000 foot-pounds per minute. Since power equals torque times rotational speed (in radians), and one revolution is 2 * Pi radians, the division of 33,000 by 2 * Pi results in approximately 5252.1. This allows direct calculation using RPM and HP without manually converting to radians first.

No. This tool calculates Full Load Torque (FLT) based on the rated power and rated speed. Starting torque, or Locked Rotor Torque (LRT), is a specific characteristic of the motor design (NEMA Design A, B, C, or D) and is typically 150% to 300% of the Full Load Torque calculated here.

Power is the product of torque and speed. If power remains constant (as is the case in the constant power region of a motor's operation curve), increasing the speed requires the torque to decrease proportionally to maintain the equation balance. This is graphically represented as a hyperbola.

Efficiency is usually found on the motor's nameplate. Standard AC induction motors typically range from 80% to 96% efficiency depending on size and classification (e.g., IE3 or NEMA Premium). Gearboxes attached to the motor will significantly lower the total system efficiency, often by 5-15% per stage.

Yes. The physics relating Power, Torque, and Speed applies to both AC and DC motors. However, DC motor torque curves can vary significantly based on voltage applied, whereas this calculator assumes operation at a specific rated power point.