Watts To Torque Calculator

Convert watts to torque in N·m from power and rpm, or find power in watts from torque, or speed from both, using P = T × ω for a rotating shaft.

• All Unit Converters
• Watts To Time Calculator
• Watts To Horsepower Calculator
• Watts To Seconds Calculator
• Watts to Volts

Calculator Functions

Function	What it does	What it requires
Torque from power and speed	Finds the torque a shaft delivers at a given power and speed	Requires the mechanical shaft power and the rotational speed
Power from torque and speed	Finds the mechanical power a shaft transmits	Requires the torque and the rotational speed
Speed from power and torque	Finds how fast a shaft turns for a given power and torque	Requires the mechanical shaft power and the torque

Power can be entered in W, kW or mechanical hp, speed in rpm or rad/s, and torque in N·m or lbf·ft. A torque result is also shown in lbf·ft and lbf·in, a power result in kW and hp, and a speed result in rad/s.

Watts to Torque Formulas

Watts do not convert to newton meters on their own, because the same power can be a small torque at high speed or a large torque at low speed. With the speed in rpm the formula becomes T = 9.5493 × P ÷ rpm. A shaft delivering 1,000 W at 1,000 rpm carries 9.549 N·m, which is 7.043 lbf·ft. The unit factors are 1 mechanical hp = 745.6999 W and 1 lbf·ft = 1.355818 N·m [1].

Torque from power and speed

A 250 W motor output at 3,000 rpm is 250 ÷ (3,000 × 2π ÷ 60) = 250 ÷ 314.16 = 0.796 N·m. The speed has to be above zero, because power divided by zero speed has no answer.

Power from torque and speed

A torque of 10 N·m at 1,500 rpm is 10 × 157.08 = 1,570.8 W, or 2.1065 hp.

Speed from power and torque

A shaft that transmits 1,000 W at 5 N·m turns at 1,000 ÷ 5 = 200 rad/s, which is 1,909.9 rpm.

Watts to N·m at Common Speeds

Speed (rpm)	N·m per 1,000 W	lbf·ft per 1,000 W
60	159.155	117.387
100	95.493	70.432
500	19.099	14.086
1,000	9.549	7.043
1,500	6.366	4.695
1,800	5.305	3.913
3,000	3.183	2.348
3,600	2.653	1.956
6,000	1.592	1.174

Torque scales in step with power at a fixed speed, so 250 W at 1,000 rpm is a quarter of the 1,000 W row: 2.387 N·m.

Limits of This Estimate

• The power is mechanical power at the shaft. The electrical watts drawn by a motor are higher, and its efficiency is needed to get from one to the other.
• Power, torque and speed must describe the same operating point. A motor’s rated watts and its no-load speed do not belong together.
• The result is not a stall or starting torque. At zero speed the shaft transmits no power whatever the torque.

Sources