How To Calculate Torque? Here’s The Mathematical Equation

Posted: April 4, 2011 in technical info
Tags: , , , , ,

Whether you’re a science student, motorist or RC enthusiast, at some point you’d like to know how much torque is your motor good for. While there are elaborate tests to determine this, here’s a mathematical formula to determine your motor or engine’s torque, using existing information you may have on Horse Power (HP), and RPM. Assuming the information you have from the manufacturer’s manual is correct, you should have an accurate figure on the motor’s torque.

Remember, we’re talking about motor or engine torque here – not the torque at the wheels – for that, it’s a whole ballgame altogether where wheel weights and dimensions play a part, and you’ll need a dynometer.

Motor Torque = HP x 5252 / RPM

Let’s do a little case study example on the HPI Nitrostar K4.6 engine that comes stock on the Savage X 4.6 and the Savage X SS.

HP = 2.9

RPM= 35,000

Going by the above equation, the Nitrostar K4.6’s torque would then be as follows:

Torque (K4.6) = 2.9 x 5252 /35000
= 0.435

That’s pretty pathetic.

On the other hand let’s see how the SH .28 base model engine would do:

HP = 3.3

RPM = 28,000

Torque (SH .28) = 3.3 x 5252 / 28,000
= 0.62.

A good 50% more.


  1. Raag90 says:

    hey there…I was interested in actually trying to calculate the torque at the wheels of my electric hub motor for a final year project….I totally agree that you have to take weight transfer into account and all…but how would I actually theoretically go on about doing this?…your explanation above was fantastic, and I would really appreciate any help..cheers

    • If your assignment concerns purely the torque at the wheels, a wheel dynamometer should do the trick! Even if it doesn’t give a torque rating, but instead a hp rating, i presume you could use the equation given.

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