Motor Torque Calculator: Find Torque from Power and RPM

Motor Torque Calculator

Find shaft torque from motor power and speed using T ft-lb = hp x 5252 / RPM and the metric form T Nm = 9548.8 x kW / RPM. Flip the calculation to solve for horsepower from torque and speed, or find the RPM a motor must spin to deliver a target torque, with instant conversion between Nm, ft-lb, kW, and hp.

⚙Choose What to Solve For

🔧Real Motor Presets

📝Motor Inputs

Motor power (rated output)

Rated shaft power the motor delivers.

Power unit

1 hp = 0.7457 kW = 745.7 W.

Rotational speed (RPM)

Shaft speed in revolutions per minute.

Torque value

Used when solving for power or speed.

Torque unit

Applies to the torque field above.

Result significant figures

Controls rounding on every result card.

Torque 0 Nm newton-meters at the shaft

Torque 0 ft-lb pound-feet at the shaft

Power 0 kW kilowatts and horsepower

Angular speed 0 rad/s omega = 2 PI RPM / 60

🔢Formula Snapshot

5252hp-rpm constant

9548.8kW-rpm constant

1.35582ft-lb to Nm

0.7457hp to kW

📋Horsepower and RPM to Torque

Power	Speed (RPM)	Torque (ft-lb)	Torque (Nm)
0.5 hp	1725	1.52 ft-lb	2.06 Nm
1 hp	1800	2.92 ft-lb	3.96 Nm
1 hp	3600	1.46 ft-lb	1.98 Nm
2 hp	1750	6.00 ft-lb	8.14 Nm
5 hp	1750	15.01 ft-lb	20.35 Nm
10 hp	1800	29.18 ft-lb	39.57 Nm
25 hp	1180	111.3 ft-lb	150.9 Nm
50 hp	1770	148.4 ft-lb	201.2 Nm

🧭Kilowatts and RPM to Torque

Power (kW)	Speed (RPM)	Torque (Nm)	Torque (ft-lb)
0.75 kW	1440	4.97 Nm	3.67 ft-lb
1.5 kW	1450	9.88 Nm	7.29 ft-lb
2.2 kW	2880	7.30 Nm	5.38 ft-lb
3 kW	1450	19.76 Nm	14.57 ft-lb
4 kW	1465	26.07 Nm	19.23 ft-lb
5.5 kW	2900	18.11 Nm	13.36 ft-lb
7.5 kW	1470	48.72 Nm	35.94 ft-lb
11 kW	1460	71.94 Nm	53.06 ft-lb

📏Unit Conversions and Constants

Quantity	Equals	Reverse	Note
1 hp	0.7457 kW	1 kW = 1.341 hp	Mechanical horsepower
1 hp	745.7 W	1 W = 0.001341 hp	Watt form of hp
1 ft-lb	1.35582 Nm	1 Nm = 0.73756 ft-lb	Torque conversion
hp constant	5252 hp-rpm	33000 / (2 PI)	ft-lb basis
kW constant	9548.8 kW-rpm	60000 / (2 PI)	Nm basis
1 RPM	0.10472 rad/s	2 PI / 60	Angular speed

🔁RPM to Angular Speed

Speed (RPM)	Omega (rad/s)	Revolutions/s	Common Use
750	78.54 rad/s	12.5 rev/s	8-pole 60Hz motor
1180	123.6 rad/s	19.7 rev/s	6-pole load rating
1450	151.8 rad/s	24.2 rev/s	4-pole 50Hz motor
1750	183.3 rad/s	29.2 rev/s	4-pole 60Hz motor
3000	314.2 rad/s	50.0 rev/s	2-pole 50Hz servo
3600	377.0 rad/s	60.0 rev/s	2-pole 60Hz motor

🗃Power vs Torque Comparison Grid

Power (hp)	Power (kW)	Torque @ 1800 rpm	Torque @ 3600 rpm	Omega @ 1800	Typical Use
0.5 hp	0.37 kW	1.46 ft-lb	0.73 ft-lb	188.5 rad/s	Small fan, blower
1 hp	0.75 kW	2.92 ft-lb	1.46 ft-lb	188.5 rad/s	Bench grinder
2 hp	1.49 kW	5.84 ft-lb	2.92 ft-lb	188.5 rad/s	Air compressor
3 hp	2.24 kW	8.75 ft-lb	4.38 ft-lb	188.5 rad/s	Table saw, pump
5 hp	3.73 kW	14.59 ft-lb	7.29 ft-lb	188.5 rad/s	Dust collector
7.5 hp	5.59 kW	21.88 ft-lb	10.94 ft-lb	188.5 rad/s	Conveyor drive
10 hp	7.46 kW	29.18 ft-lb	14.59 ft-lb	188.5 rad/s	Hydraulic pump
15 hp	11.19 kW	43.77 ft-lb	21.88 ft-lb	188.5 rad/s	Machine tool
25 hp	18.64 kW	72.94 ft-lb	36.47 ft-lb	188.5 rad/s	Large blower
50 hp	37.29 kW	145.9 ft-lb	72.94 ft-lb	188.5 rad/s	Process pump

🔧Formula Breakdown

T ft-lb = hp x 5252 / RPMTorque in pound-feet equals horsepower times 5252 divided by speed. The 5252 comes from 33000 ft-lb per minute per hp divided by 2 PI, so it is the RPM where the hp and torque curves cross on a dyno chart.

T Nm = 9548.8 x kW / RPMThe metric form. 9548.8 equals 60000 divided by 2 PI, converting kilowatts and RPM directly into newton-meters. For example 7.5 kW at 1470 rpm gives 9548.8 x 7.5 / 1470 = 48.7 Nm.

hp = T ft-lb x RPM / 5252Rearranged to find power from a measured torque and speed. A shaft turning 1750 rpm at 15 ft-lb produces 15 x 1750 / 5252 = 5.0 hp.

kW = T Nm x RPM / 9548.8The metric power form. 48.7 Nm at 1470 rpm returns 48.7 x 1470 / 9548.8 = 7.5 kW, closing the loop with the example above.

omega = 2 PI x RPM / 60Angular speed in radians per second. At 1750 rpm, omega = 2 PI x 1750 / 60 = 183.3 rad/s. This links the two forms since Power in watts = Torque in Nm x omega.

Unit bridges1 hp = 0.7457 kW and 1 ft-lb = 1.35582 Nm. Multiply ft-lb by 1.35582 to reach Nm, and multiply hp by 0.7457 to reach kW, which is how all four result cards stay consistent.

💡Motor Sizing Tips

Torque trades against speed: At fixed power, halving the RPM doubles the torque. A 5 hp motor makes about 15 ft-lb at 1750 rpm but roughly 7.3 ft-lb at 3600 rpm. If your load needs more torque, a gearbox that drops output speed 10 to 1 raises available torque nearly 10 to 1, minus gear losses of a few percent.

Watch the 5252 crossover: Because T ft-lb = hp x 5252 / RPM, every motor produces its rated horsepower and its rated torque as equal numbers at exactly 5252 rpm. Below 5252 rpm torque exceeds the hp figure, and above it torque is smaller. Use the rated nameplate RPM, not the synchronous speed, for accurate sizing on induction motors that slip 1 to 3 percent.

In motors, we don’t pick them by their horsepower rating. We pick them by amount of torque they deliver so that as load increases, the motor won’t stall out. Torque is what let the motor begin working immediately. Power is how much work the motor can do over time. In industry, this makes all the difference because a stalled motor will cost more then an hour’s worth of someone’s time.

Once you know speed and rated power, calculator does the math for you. Removing the conversions and coefficients from equation allows it to stay physically accurate without the guesswork. Power is torque times rotational speed. The standard SI units for that equation are Newtons-meter × Radians/second, which works out to watts. Since no one displays their nameplate with radians on a motor, or often even watts, engineers simply bake some unit conversion into a couple handy constants.

How to Choose the Right Motor Torque

The constant 5252 ties horsepower to pound-feet; 9548.8 links newton-meters to kilowatts. These values comes from dividing the usual power-per-minute definition by two pi radians. It’s not magic, it’s just arithmetic expressed in terms you’re used to. One of those handy numbers to remember when trying to get your head around things is the magic 5252.

For example, if you have a motor turning 5,252 RPM, it’s producing an equal amount of pounds of torque as it is horsepower. Anything over or under will see the horsepower and torque figure flip-flop. Why is that important? On some dyno charts, you’ll notice where two lines cross somewhere in the mid-range speeds. That crossover number happen to be 5,252 RPM. So what does that tell us? Not to assume something is high horsepower because it must also have high torque at low rpm.

Mostly it’s solving for torque. Multiply rated power by constant and divide by speed. At 1750 RPM, a five horsepower motor will generate roughly fifteen pound-feet of torque. Double that speed to 3500 RPM and the torque halve to seven point five pound-feet while power output stays the same. It figures out your answer in imperial units as well as metric, letting you read newton-meters without having to run a conversion on a different calculator. That’s good since it’s easy to make transcription errors when copying values from spec sheets.

Sometimes we must make those reverse calculations. Perhaps you know the amount of twist in a shaft, measured by some sort of load cell. Or maybe you want to calculate how much power is demanded by given torque. Or perhaps you have a desired torque, but you already have a motor and it cannot spin any faster. What gear ratio should be used to multiply the force and slow the shaft? The calculator will rearrange it with ease. If you feed in all but one variable, it will make that variable the output rather than the input. This allows for flexibility when specs is missing or conflicting.

Whenever there’s power, there’s a tradeoff between speed and torque. Add more power, and you can give up some rotation speed or get more turning force. That’s where gearboxes comes into play. Reducing the output speed by 10:1 multiplies the torque by almost 10:1, before any losses from heat and friction.

Remember when sizing a drive (use nameplate RPM), not the theoretical synchronous speed. Induction motors will slip one to three percent under load, which if ignored will shift your torque estimate enough to cause startup trouble. Experienced engineers are surprised at how often they gets confused by unit conversions. A pound-foot is approximately equal to 1.36 newton-meters. Similarly, one horsepower is about 0.75 of a kilowatt. When browsing an international datasheet, it can help to remember those ratios.

Fortunately, most common motor sizes convert between systems as shown in the reference tables on page. If the tool will do the conversion for you then there’s no need to memorize, but understanding the rough ratios allows you to catch glaring mistakes in your input data. Torque matters, too little and your motor will stall when loaded down; too much and it’s wasted money and energy from an oversized motor. Getting torque wrong is actualy expensive.

What this tool does well is that it provides answers for either torque or speed needs. From a technician sizing a conveyor drive to a student studying the fifty-two-fifty-two rule, you can input variables and have confidence in quick results. It starts where it should of: with physics and ends at the appropriate motor selection.