In physics, mass is usually measured in kilograms. Metric weighing-scales will usually display mass in kilograms, so this is a likely choice for the measurement of a person's mass.
The SI base unit for mass is the kilogram.
A Newton.
Kilograms
One US gallon of producer's milk (not skimmed, semi-skimmed, homogenised etc), weighs 10.1 pounds-force in customary measure and 44.5 newton in metric measure.
It is 10 grams. A gram is part of the metric system.
a metric tonne, 1000Kg or about 2207.6 lbs
There is no set measurement for this, because it varies from person to person. If you wish to measure it with existing metric units, however, the best option would be centimeters because a meter is much too large, while it is very difficult to come across something that measures in decimeters.
Metre, although the metric system also offers simple multiples of metres to measure much longer or shorter distances.
Either grams or kilograms - depending on the size of the potato.
Grams.
One US gallon of producer's milk (not skimmed, semi-skimmed, homogenised etc), weighs 10.1 pounds-force in customary measure and 44.5 newton in metric measure.
1 US gallon = 3.78541178 liters. Only if you mean pure water, then 1000 litres of water weighs 1 metric tonne. 1000 litres of water are 264.172052357 gallons that weigh 1 metric tonne.
CENTIMETERS
One metric ton weighs 1000kilograms.
As a potato chip is light weight I would use grams and milligrams.
A metric ton weighs 2200 pounds. Also called a "long ton".
Acrocanthosaurus weighed 6.17 metric tons/ 6.8 short tons.
For a desk like one used in schools the best unit would be pounds. Good luck on your measuring!
That's about 2,205 pounds if the object is on the earth. The same metric ton weighs about 360 pounds on the moon.
1 mile = 1.609344 kilometres.