Convert Ounces to Grams

The formula

To convert ounces to grams, multiply the ounce value by the exact conversion factor:

g = oz × 28.349523125

• g — the result in grams.
• oz — the input weight in avoirdupois ounces.
• 28.349523125 — the exact number of grams per ounce, fixed by the 1959 International Yard and Pound Agreement (1 lb = 0.45359237 kg exactly; 1 oz = 1/16 lb, so 1 oz = 0.45359237/16 = 0.028349523125 kg = 28.349523125 g).

Worked example

Using the calculator’s default input of 8 oz:

1. Take the ounce value: 8.
2. Multiply by 28.349523125: 8 × 28.349523125 = 226.796.

So 8 oz ≈ 226.80 g. A half-pound (8 oz) is a useful benchmark — roughly 227 g.

Conversion table

Common ounce values converted to grams (avoirdupois):

Ounces (oz)	Grams (g)
0.5	14.17
1	28.35
2	56.70
3	85.05
4	113.40
5	141.75
6	170.10
7	198.45
8	226.80
10	283.50
12	340.19
16	453.59
24	680.39
32	907.18

History & standards

The avoirdupois ounce descends from the medieval “avoir de pois” (French: goods of weight) system used for trade across England and France. It is defined as 1⁄16 of an avoirdupois pound, making 16 oz = 1 lb. Since the 1959 International Yard and Pound Agreement fixed 1 lb = 0.45359237 kg, the ounce has an exact metric equivalent: 28.349523125 g.

There is also a troy ounce (31.1035 g, or about 10% heavier), descended from the Troyes market in medieval France and used for precious metals — gold, silver and platinum are still priced per troy ounce on commodity markets. Always check which ounce a source means; this calculator uses the avoirdupois ounce.

The gram is one thousandth of the kilogram — the SI base unit of mass. Since 2019 the kilogram is defined by fixing the Planck constant, giving the gram a permanent, artefact-free definition.

Common applications

• Cooking and baking. Adapting US recipes (which use ounces) to metric scales, or converting European/UK recipes to US cups and ounces.
• Food labelling. US nutrition labels display serving sizes in both grams and ounces; cross-checking between products from different countries.
• Postal and parcel services. Many carriers, particularly in the US, charge by the ounce for small items; kitchen and postal scales typically read in grams.
• Craft and hobby. Yarn is sold by ounces in the US and grams elsewhere; knitting and crochet patterns specify amounts in one or both units.
• Coffee and tea. Specialty coffee is sold in 12 oz or 16 oz bags in the US, while European roasters sell in 250 g or 500 g bags.

Reverse conversion

To convert grams back to ounces, divide by 28.349523125: oz = g ÷ 28.349523125 — or use our grams to ounces calculator.

Limitations & gotchas

• Avoirdupois vs troy. Precious-metal prices are quoted in troy ounces (31.1035 g). Using this calculator for gold or silver will give you the wrong answer — use a troy-ounce converter instead.
• Fluid ounces are not weight ounces. A US fluid ounce measures volume (≈29.57 mL), not mass. Converting fluid ounces to grams requires knowing the density of the liquid.
• Rounding. The exact factor is 28.349523125 g; rounding to 28.35 introduces an error of <0.0002% — negligible for everyday purposes but worth noting for precise pharmaceutical or scientific work.

Sources & references

• NIST SP 811 — Guide for the Use of the International System of Units (SI).
• BIPM — The International System of Units (SI), 9th edition (2019).
• 1959 International Yard and Pound Agreement (fixing 1 lb = 0.45359237 kg exactly).