Torque is a rotational force that’s critical in a lot of mechanical systems. It’s a measure of how much a force acting on an object causes that object to rotate.
This article will explain how to convert between kilogram-meters (kgm) and foot-pounds (ft-lbs). The kilogram-meter (kgm) and the foot-pound (ft-lb) are both units used to measure torque. You might also see torque measured in Newton-meters (Nm), Kilogram-force centimeter (kgf-cm), or even Joules per radian (J/rad).
Understanding the Units: Kilogram-Meters (kgm) and Foot-Pounds (ft-lbs)
Before we get to the conversion, let’s make sure we’re all on the same page about what these units mean.
Kilogram-Meters (kgm)
A kilogram-meter (kgm) is a unit of torque. Think of it as the amount of turning force that results from a one-kilogram weight acting at a right angle one meter away from the center of rotation.
Technically, kg-m should be written as kgf-m (kilogram-force meter) to really drive home the fact that we’re talking about the force of gravity acting on that kilogram mass.
Foot-Pounds (ft-lbs)
Foot-pounds (ft-lbs) measure torque in the imperial system. One foot-pound is the torque resulting from a one-pound force acting at a right angle one foot away from the axis of rotation.
Just to be clear, foot-pounds (ft-lbs) measure torque. That’s different from pounds-force, which measures just plain old force.
How to convert kgm to ft-lbs
The trick to converting kilogram-meters (kgm) to foot-pounds (ft-lbs) is to go through Newton-meters (Nm) first. Here’s how it works:
- kgm to Nm: 1 kgm equals 9.80665 Nm.
- Nm to ft-lbs: 1 Nm equals 0.7376 ft-lbs (or, flipped around, 1 ft-lb equals 1.3558 Nm).
So, to jump straight from kgm to ft-lbs, we do a little multiplication:
9.80665 Nm/kgm 0.7376 ft-lbs/Nm ≈ 7.233 ft-lbs/kgm
That means 1 kgm is about 7.233 ft-lbs. To convert from kgm to ft-lbs, multiply the kgm value by 7.233.
Example: 5 kgm is about 5 7.233 ft-lbs, which equals 36.165 ft-lbs.
How to use kg to ft lbs: Examples
Let’s say you’re working on your car. The repair manual specifies the torque needed to tighten a bolt in foot-pounds (ft lbs), but your torque wrench only displays kilogram-force meters (kg). You’ll need to convert kg to ft lbs to get the correct torque and avoid damaging the bolt or other parts.
This type of conversion is also important when designing gear trains. Using the wrong torque measurements in your calculations could lead to serious errors.
Other torque units and conversions
Torque can be expressed in various units, including Newton-meters (Nm), Kilogram-force centimeters (kgf-cm), and Joules per radian (J/rad).
A Joule per radian is equivalent to a Newton-meter (1 J/rad = 1 Nm).
Conversions to Nm
To convert from kilogram-force centimeters to Newton-meters, use this formula:
1 kgf-cm = 0.09807 Nm
To convert from kilogram-force centimeters to foot-pounds, use this formula:
1 kgf-cm = 0.07233 ft-lbs
Conversion to inch-lbs
To convert from Newton-meters to inch-pounds, use this formula:
1 Nm = 8.851 in-lbs
To convert from foot-pounds to inch-pounds, use this formula:
1 ft-lb = 12 inch-lbs
Conclusion
Knowing how to convert between kilogram-meters (kg-m) and foot-pounds (ft-lbs) is vital for anyone working with mechanical systems. These units measure torque, or rotational force.
To convert from kg-m to ft-lbs, remember that 1 kg-m equals 7.233 ft-lbs. Understanding and applying this conversion factor ensures that torque calculations are accurate.
Precise torque measurements are essential for the proper functioning and safety of mechanical devices, big and small.