Question 1

What is the difference between mass and weight?

Accepted Answer

Mass (kg) is the amount of matter and never changes with location. Weight (newtons) is the force of gravity and depends on g. On the Moon a 70 kg mass weighs about 114 N — one sixth of its Earth weight. In everyday speech "weight" usually means mass, which is fine.

Question 2

Why are pounds and ounces different in different systems?

Accepted Answer

History left several systems. Avoirdupois (trade): 1 pound = 16 ounces = 453.6 g. Troy (precious metals): 1 troy pound = 12 troy ounces = 373.2 g, with a troy ounce of 31.1 g — gold is priced per troy ounce.

Question 3

What is a "metric pound"?

Accepted Answer

It is an informal unit equal to 500 g. Historically the Russian pound was 409.5 g, and "half a kilo" was loosely called a pound in old shops. The term is now obsolete.

Question 4

How are gold and diamonds weighed?

Accepted Answer

Gold and silver are weighed in troy ounces (31.1035 g). Diamonds and other gemstones use carats (1 carat = 0.2 g). A 1-carat diamond is about the size of a little-fingernail tip. The largest rough diamond, the Cullinan, was 3,106.75 carats.

Question 5

Is a "ton" metric or imperial?

Accepted Answer

A metric tonne is 1,000 kg. The long (British) ton is 1,016 kg = 2,240 pounds, and the short (US) ton is 907 kg = 2,000 pounds. When importing coal or metal, check whether it is "MT" (metric ton) or "short ton" — the 10% difference changes the numbers.

Mass & Weight Converter — Free Online Calculator