Ounces to Grams Formula Explained

4 min read•June 1, 2025•Reviewed: June 1, 2026

✓Reviewed by Apex Conversion Editorial Team · Last reviewed June 1, 2026

To convert ounces to grams, multiply by 28.3495. One avoirdupois ounce is defined as exactly 28.349523125 grams — a precise value established by international agreement in 1959. This is the ounce used for food, body weight, shipping, and all everyday contexts outside precious metal trading.

A common mistake is confusing fluid ounces (a volume unit, ≈ 29.6 mL) with weight ounces (a mass unit, 28.35 g). They are completely different. This article concerns weight ounces only.

The Formula

g = oz × 28.3495

Worked examples:
   1 oz × 28.3495 =   28.35 g
   2 oz × 28.3495 =   56.70 g
   4 oz × 28.3495 =  113.40 g  (¼ lb)
   8 oz × 28.3495 =  226.80 g  (½ lb)
  12 oz × 28.3495 =  340.19 g  (¾ lb)
  16 oz × 28.3495 =  453.59 g  (1 lb)
  32 oz × 28.3495 =  907.18 g  (2 lb)

Quick estimate: multiply oz by 28 (within 0.2%)
  8 oz × 28 = 224 g  (exact: 226.8 g)

Where 28.3495 Comes From

The avoirdupois ounce is 1/16 of a pound. The pound is defined as exactly 453.59237 grams. Therefore: 453.59237 g ÷ 16 = 28.349523125 g per ounce. This chain of exact definitions makes the conversion factor mathematically exact.

28.3495 is rounded to 4 decimal places. Using this value introduces an error of less than 0.0001% — far below what any kitchen scale or postal scale can measure. For almost all practical purposes, 28.35 is adequate.

Avoirdupois vs. Troy Ounce

The troy ounce used for precious metals equals 31.1034768 grams — about 10% heavier than the avoirdupois ounce. If you are converting gold, silver, or platinum weights, multiply troy ounces by 31.1035 instead of 28.3495.

Gold jewelry is often labeled in either troy ounces or grams. A 1-troy-oz gold coin weighs 31.10 g. If you mistakenly apply the avoirdupois formula, you would calculate 28.35 g — 2.75 g short, which represents significant value at precious metal prices.

Quick Tips

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Multiply by 28.35 for everyday cooking — accurate to 5 significant figures.
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Multiply by 28 for quick mental math — off by less than 1.2%.
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4 oz = 113.4 g, 8 oz = 226.8 g, 16 oz = 453.6 g — memorize these three.
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For precious metals only: multiply troy oz by 31.1035 instead.
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Don't confuse oz (weight) with fl oz (fluid ounces, a volume measure).

Frequently Asked Questions

What is 4 oz in grams?

4 × 28.3495 = 113.4 g. This is one quarter pound — a very common serving size for meat, fish, and cheese.

What is 8 oz in grams?

8 × 28.3495 = 226.8 g. Half a pound — the standard US medium package size for many dairy and deli products.

What is 16 oz in grams?

16 × 28.3495 = 453.6 g = exactly 1 lb. This is the fundamental relationship: 1 lb = 16 oz = 453.592 g.

Why do food packages sometimes show different gram values for the same ounce weight?

Rounding. A package labeled '8 oz' might show 226 g, 227 g, or 228 g on the metric side — these are all valid roundings of the exact 226.796 g. The difference is insignificant for food.

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