Weight is defined as the force of gravity on an object. Mass is the total amount of matter in an object. Mass and weight are often used interchangeably. People usually refer to the mass and weight for the same purpose but both are differently measured. The weight of a person or a thing depends on the gravitational force of the place where that person or thing is right now. The mass of a person or a thing does not depend on the gravitational force but it remains the same irrespective of the place where the person or the thing is at the moment. A person weighing 60kg on the earth will weigh less on the moon as the gravity on the moon is less than that on the earth.
The formula of the weight is W = mg where m is the mass of the object and g is the acceleration due to gravity. When the weight is measured on a weighing scale, it measures the force of gravity on the object being measured and gives the result as the mass of that object. Thus, we often misconceive mass as weight.
The unit of weight in the SI unit system is Newton while the unit of mass in the SI unit system is kilogram. The other units of mass are derived from kilogram such as gram, milligram, microgram and so on. There is no different concepts of mass and weight in the British Imperial System and the United States Customary Units system. The most commonly used units of mass or weight in these systems are pound, ounce, stone, and ton.
| kg | mg | gram | pound | ounce | stone | metric ton | US ton | Imperial ton | |
| 1 kg | 1 | 1000000 | 1000 | 2.20462 | 35.274 | 0.157473 | 0.001 | 0.00110231 | 0.000984207 |
| 1 mg | 0.000001 | 1 | 0.001 | 2.20462e-6 | 3.5274e-5 | 1.57473e-7 | 1e-9 | 1.10231e-9 | 9.84207e-10 |
| 1 gram | 0.001 | 1000 | 1 | 0.00220462 | 0.035274 | 0.000157473 | 1e-6 | 1.10231e-6 | 9.84207e-7 |
| 1 pound | 0.453592 | 453592 | 453.592 | 1 | 16 | 0.0714286 | 0.000453592 | 0.0005 | 0.000446429 |
| 1 ounce | 0.0283495 | 28349.5 | 28.3495 | 0.0625 | 1 | 0.00446429 | 2.83495e-5 | 3.125e-5 | 2.79018e-5 |
| 1 stone | 6.35029 | 6.35e+6 | 6350.29 | 14 | 224 | 1 | 0.00635029 | 0.007 | 0.00625 |
| 1 Metric ton | 1000 | 1e+9 | 1000000 | 2204.62 | 35274 | 157.473 | 1 | 1.10231 | 0.984207 |
| 1 US ton | 907.185 | 9.072e+8 | 907185 | 2000 | 32000 | 142.857 | 0.907185 | 1 | 0.892857 |
| 1 Imperial ton | 1016.05 | 1.016e+9 | 1.016e+6 | 2240 | 35840 | 160 | 1.01605 | 1.12 | 1 |
