An ounce is a customary and imperial unit used for small weights. It appears on food labels, postal and shipping scales, recipes, packaged goods, cosmetics, supplements, precious metals, and many consumer products.
Quick facts
- Unit name
- ounce
- Plural
- ounces
- Symbol
- oz
- Quantity
- mass in everyday conversion
- System
- US customary and imperial
- Gram relation
- 1 oz = 28.349523125 g
- Pound relation
- 16 oz = 1 lb
- Kilogram relation
- 1 oz = 0.028349523125 kg
Visual scale
One ounce is much smaller than a pound and a little under 30 grams, making it useful for small goods and portions.
Definition and exact value
In ordinary weight conversion, ounce usually means the avoirdupois ounce. One avoirdupois ounce is exactly one sixteenth of a pound and equals exactly 28.349523125 grams.
Symbol and writing rules
The common symbol for ounce is oz. Unit symbols are not pluralized in technical writing, so use 1 oz and 12 oz. In prose, write "1 ounce" and "12 ounces".
Avoirdupois, troy, and fluid ounces
The word ounce can refer to different units. The avoirdupois ounce is used for ordinary weight. The troy ounce is used for precious metals. The fluid ounce measures volume, not weight.
| Ounce type | Measures | Typical use | Relationship |
|---|---|---|---|
| avoirdupois ounce | mass | food, packages, everyday weight | 1 oz = 28.349523125 g |
| troy ounce | mass | gold, silver, precious metals | different from ordinary oz |
| fluid ounce | volume | liquids, recipes, beverages | not a weight unit |
How heavy is one ounce?
One ounce is useful for small weights and portions. It is common when a pound is too large and grams are not the expected unit for the audience.
Food scale
Snack packages, meat portions, coffee, cheese, and dry ingredients may use ounces.
Package scale
Small parcels and postal weights often use ounces before reaching pound-scale values.
Retail scale
Cosmetics, supplements, household products, and small goods may list ounce weights.
Ounce vs gram
The ounce is customary; the gram is metric. One ounce equals exactly 28.349523125 grams, so ounce-to-gram conversion commonly produces decimals.
Visual comparison
Ounce vs pound
Ounces and pounds are part of the same everyday customary weight system. Use ounces for smaller quantities and pounds for larger quantities. One pound equals exactly 16 ounces.
Common uses
- Food labels, recipe weights, snacks, coffee, meat, cheese, and dry ingredients.
- Postal weights, small parcels, ecommerce packages, and carrier labels.
- Cosmetics, supplements, soaps, candles, and consumer packaged goods.
- Fitness, nutrition, meal prep, and US customary kitchen measurements.
How ounces are measured
Ounces are measured with scales that support small weights. Kitchen scales, postal scales, and retail scales often display ounces, pounds and ounces, grams, or kilograms.
- Check whether the scale is showing oz, lb, g, or kg.
- Tare the container if it should not be included.
- For pounds and ounces, remember that 16 oz equals 1 lb.
Precision and rounding
For recipes and small packages, one decimal place in ounces may be enough. For labels, postage, supplements, or product specifications, follow the required precision and avoid rounding before conversion.
Conversion formulas
Ounce conversion table
| Ounces | Grams | Pounds | Kilograms |
|---|---|---|---|
| 1 oz | 28.349523125 g | 0.0625 lb | 0.028349523125 kg |
| 4 oz | 113.3980925 g | 0.25 lb | 0.1133980925 kg |
| 8 oz | 226.796185 g | 0.5 lb | 0.226796185 kg |
| 16 oz | 453.59237 g | 1 lb | 0.45359237 kg |
| 32 oz | 907.18474 g | 2 lb | 0.90718474 kg |
Common mistakes
- Confusing oz and fl oz: ounce is weight or mass; fluid ounce is volume.
- Confusing ordinary ounces and troy ounces: precious metals use troy ounces, not ordinary avoirdupois ounces.
- Forgetting 16 oz per pound: 8 oz is half a pound, not eight tenths of a pound.
- Using 28 g as exact: 1 oz equals exactly 28.349523125 g.
- Rounding too early: small package weights can be affected by early rounding.
Related Xunits pages
Ounce converters
Weight references
FAQ
How many grams are in one ounce?
One avoirdupois ounce equals exactly 28.349523125 grams.
How many ounces are in one pound?
One pound equals exactly 16 ounces.
What is the symbol for ounce?
The common symbol is oz.
Is ounce the same as fluid ounce?
No. Ounce is a weight or mass unit. Fluid ounce is a volume unit.
Is a troy ounce the same as a regular ounce?
No. A troy ounce is used for precious metals and has a different mass from the ordinary avoirdupois ounce.
Should I use ounces or grams?
Use ounces for US customary labels and recipes. Use grams for metric labels, nutrition, lab work, and international product specifications.
Reference notes
This guide uses the ordinary avoirdupois ounce used in everyday weight conversion: 1 oz = 28.349523125 g and 16 oz = 1 lb.