PRIMARY UNITS IN THIS GUIDE ARE METRIC
(SI - THE INTERNATIONAL SYSTEM OF UNITS):

LENGTH

m

METER

MASS

g

GRAM

FORCE

mN

MILLINEWTON

TORQUE

mN·m

MILLINEWTON METER

INERTIA

g·m²

GRAM METER²

In this system, mass is always in kilograms or grams. Force, or weight is always in newtons or millinewtons.

Force (or weight) = Mass × Acceleration

F = ma

when a = 9.81 m/sec² (acceleration due to gravity), then F would be the weight in newtons.

A spring scale reading of 1 kg means that you are measuring a mass of 1 kg.

A spring scale reading of 2.2 lb also is measuring a mass of 1 kg.

If you use that same spring scale to measure a force, the 1 kg reading must be multiplied by 9.8 to give a force of 9.8 newtons. The reading of 2.2 lb us a force and is equal to 9.8 newtons.

If the same scale is used to measure torque (T = FR) at one meter radius, the reading of 1 kilogram × 1 meter = 1 kgm must be multiplied by 9.8 to give a torque of 9.8 newton meters (N·m).