The ounce (abbreviated oz) is a unit of mass (or weight); in the form fluid ounce (fl oz) it is a unit of volume. It’s commonly used in cooking, shipping, and pricing precious metals.
Explanation
- Origin: The word “ounce” comes from Latin uncia meaning “one-twelfth.”
- Abbreviations: use oz for weight/ mass ounce and fl oz (or “fl. oz.”) for fluid ounce.
Main types of ounce
- Avoirdupois ounce (common everyday weight): $1\text{ oz} = 28.349523125\text{ g}$.
- Relationship with pounds: $1\text{ lb} = 16\text{ oz}$ (avoirdupois).
- Troy ounce (used for precious metals like gold, silver): $1\text{ troy oz} = 31.1034768\text{ g}$.
- Note: the troy pound is $12\text{ troy oz}$ (different from avoirdupois pound).
- Fluid ounce (volume — different in US vs. Imperial):
- US fluid ounce: $1\text{ fl oz (US)} = 29.5735295625\text{ mL}$.
- Imperial (UK) fluid ounce: $1\text{ fl oz (Imp)} = 28.4130625\text{ mL}$.
Quick conversions (useful examples)
- Recipe: “2 oz butter” → $2\text{ oz}\times 28.3495\text{ g/oz}\approx 56.70\text{ g}$.
- Steak: “12 oz steak” → $12\text{ oz}\times 28.3495\text{ g/oz}\approx 340.19\text{ g}$.
- Gold price: “1 oz gold” usually means $1\text{ troy oz} = 31.1035\text{ g}$.
- Liquid: “1 US cup = 8 fl oz (US)” so $1\text{ cup (US)} = 8\times 29.5735\text{ mL} \approx 236.59\text{ mL}$.
- Beer: US pint = 16 fl oz (US); Imperial pint = 20 fl oz (Imp).
When to use which ounce
- Use avoirdupois ounce (oz) for food, postal weights, most everyday objects.
- Use troy ounce (troy oz) when dealing with precious metals and jewelry.
- Use fluid ounce (fl oz) for liquid volumes in recipes and beverages — check whether US or Imperial units apply.
Tip: If you see “oz” with no qualifier and the context is food or packages, it’s almost always the avoirdupois ounce. If the context is gold/silver, assume troy ounce. If the context is liquids, look for “fl oz.”
If you want, I can convert a specific quantity for you (e.g., convert 7 oz butter to grams, or convert 3 fl oz (US) to mL). Which example would you like?