# US Standard Mass (Weight)

Mass: how much matter is in an object.

We measure mass by weighing, but Weight and Mass are not really the same thing.

These are the most common measurements of mass:

 Ounces Pounds Tons

### The Ounce

 The smallest unit of mass is ounces (oz).  One ounce weighs about the same as a slice of bread.  It is very light.   The abbreviation for ounce is "oz", because it came from the 15th century Italian word "onza".

But be careful: "Ounce" and "Fluid Ounce" are different!

• Ounce is mass
• Fluid Ounce is volume

Here we talk about ounce as a mass.

When you get lots of ounces you get a new label:

### The Pound

 If you have 16 ounces, it can also be called a pound (lb).  1 pound = 16 ounces The abbreviation is "lb", because it came from the Latin word "libra". Typically, this is the unit that you use to measure your own weight.  Pounds are used to measure lots of things from people to food to animals.

However, if something is very heavy we use yet another label:

### The Ton

 2,000 pounds is also one ton.  1 ton = 2,000 pounds That is really heavy!  Trucks, ships and heavy equipment are measured using tons instead of pounds. An elephant has a mass of about 7 tons
 And this car is about 2 tons.
 But in some countries a "ton" can mean 2,240 pounds, so to be clear use "short" and "long" in front of "ton", like this: A Short Ton is 2,000 pounds A Long Ton is 2,240 pounds

1 pound = 16 ounces

1 ton (also called "short ton") = 2,000 pounds = 32,000 ounces

1 long ton = 2,240 pounds

## Weight or Mass?

We have used the word "weight" only because that is what people commonly say.

But we really should say "Mass". See Weight or Mass to learn more.

"Ounce" normally means "Avoirdupois Ounce", but there is also "Troy Ounce"

• The International avoirdupois ounce is 28.349523125 grams (normal meaning of "ounce")
• The International troy ounce is 31.1034768 grams

## More Examples

An ounce of mass is:

• exactly 28.349523125 grams

A pound is:

• a bit less than half a kilogram
• exactly 453.59237 grams (so a pound has a metric definition)

A short ton is:

• about the weight of a small car
• exactly 907.18474 kilograms

A long ton is:

• very close to 1 tonne (1,000 kilograms)
• exactly 1016.0469088 kilograms