An ounce can mean three different things: (1) Avoirdupois ounce (oz) = 28.3495 grams, used for general weighing; (2) Fluid ounce (fl oz) = 29.5735 mL (US) or 28.4131 mL (Imperial), used for liquid volume; (3) Troy ounce (oz t) = 31.1035 grams, used for precious metals.

Is a fluid ounce the same as a regular ounce?

No. A fluid ounce measures volume while a regular (avoirdupois) ounce measures weight. One fluid ounce of water weighs approximately one avoirdupois ounce, but this is a coincidence. Other liquids differ: a fluid ounce of honey weighs about 1.5 oz.

How many grams are in an ounce?

One avoirdupois ounce equals approximately 28.3495 grams. One troy ounce (used for gold and silver) equals approximately 31.1035 grams.

What Is an Ounce? Weight vs Fluid Ounces Explained

Three Types of Ounces

Type	Symbol	Measures	Equivalent
Avoirdupois ounce	oz	Weight/mass	28.3495 g
US fluid ounce	fl oz	Volume	29.5735 mL
Imperial fluid ounce	fl oz	Volume	28.4131 mL
Troy ounce	oz t	Weight (precious metals)	31.1035 g

Avoirdupois Ounce (Everyday Weight)

This is the standard ounce for weighing food, mail, and products. There are 16 avoirdupois ounces in one pound. The word "avoirdupois" comes from Old French meaning "goods of weight."

Fluid Ounce (Liquid Volume)

The fluid ounce measures volume, not weight. US and Imperial fluid ounces are different sizes. The US fluid ounce (29.57 mL) is slightly larger than the Imperial fluid ounce (28.41 mL).

Troy Ounce (Precious Metals)

When you hear "gold is $2,000 per ounce," that refers to troy ounces. A troy ounce is about 10% heavier than a regular ounce. There are 12 troy ounces in a troy pound (not 16).

Common Items Weighing About 1 Ounce

A slice of bread (~28 g)
A AA battery (~23 g, slightly under)
A standard letter envelope with paper
About 28 paper clips

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