Quick Values
Formula
Grams = Ounces × 28.3495
Ounces to Grams Converter
Type any weight in international avoirdupois ounces — meat portion from a US recipe, postage scale reading, baby weight, gym supplement scoop — and the page renders the equivalent in grams. The avoirdupois ounce (~28.35 g) is the everyday weight ounce used in US cooking, US shipping, and most English-language fitness contexts. It is NOT the same as the troy ounce (31.1035 g) used for precious metals like gold, silver, and platinum, nor is it the same as the fluid ounce (a volume unit, not a weight unit, ~29.57 mL US or 28.41 mL Imperial). If a recipe says "4 oz of butter" it means avoirdupois weight; if a precious-metals dealer quotes "1 oz of gold" it means troy weight; if a US drink recipe says "2 fl oz" it means volume.
About this tool
The conversion uses the international 1959 definition: 1 international avoirdupois ounce = 1/16 of an international avoirdupois pound = 28.349523125 grams exactly (since 1 lb = 0.45359237 kg exactly per the 1959 IYPA, Federal Register Doc 59-5442). Same factor in NIST SP 811:2008 (Thompson & Taylor) and the UK Weights and Measures Act 1985. The avoirdupois system originates from medieval Anglo-French wool trading and has been the everyday weight system in English-speaking commerce since the 14th century. Common reference points: 1 oz = 28.35 g, 2 oz = 56.70 g, 4 oz = 113.40 g (1 stick US butter), 8 oz = 226.80 g (½ pound), 16 oz = 453.59 g (1 pound), 20 oz = 566.99 g, 32 oz = 907.18 g (2 pounds, the typical US ground-beef family pack). For precious metals you need the troy ounce (1 troy oz = 31.1034768 g, used in gold/silver/platinum quotes — there's a separate Troy converter for those), and for US/UK liquid recipes you need the fluid ounce volume converter (US fl oz = 29.5735 mL, UK fl oz = 28.4131 mL).
- Exact international avoirdupois ounce factor (1 oz = 28.349523125 g)
- Distinguishes from troy ounce (31.10 g, precious metals)
- Distinguishes from fluid ounce (volume, ~29.57 or 28.41 mL)
- Live conversion as you type — no Convert button
- Quick presets for cooking-relevant weights (4 oz butter stick, 16 oz pound)
- Swap button to flip to the reverse grams-to-oz page
- Copy result with a single click
- Accepts decimal oz input for fractional ounces
- No upload — every conversion runs locally in your browser
- Useful for US recipes, postage, fitness, baby weight, ammo casings
Free. No signup. Your inputs stay in your browser. Ads via Google AdSense (consent required).
Frequently asked questions
Why is "1 oz = 28.349523125 g" exact?
The avoirdupois ounce is anchored to the international avoirdupois pound, which the 1959 International Yard and Pound Agreement (Federal Register Doc 59-5442, effective 1 July 1959) defined as exactly 0.45359237 kg for six countries — the United States, the United Kingdom, Canada, Australia, New Zealand and South Africa. Dividing by 16 ounces per pound yields 0.45359237 / 16 = 0.028349523125 kg = 28.349523125 g per ounce, exact by definition. Before 1959 each country had a slightly different ounce (the US "old" pound differed from the UK by parts per million); the agreement froze the value at the level of measurement uncertainty in the kilogram itself. Same factor in NIST SP 811:2008 and the UK Weights and Measures Act 1985.
What's the difference between avoirdupois ounce and troy ounce?
Two distinct units sharing the name "ounce". The avoirdupois ounce (28.349523125 g, 16 oz per avoirdupois pound) is the everyday weight ounce — used in US cooking, US shipping, postage, and most English-language fitness contexts. The troy ounce (31.1034768 g, 12 troy oz per troy pound, established by the Verdict of the Trial of the Pyx of 18 Henry VIII (1527, preceded by royal proclamation 5 November 1526) replacing the earlier tower pound) is the precious-metals quotation unit — gold, silver, platinum and palladium are quoted per troy oz, as are pharmaceutical grain weights. The two ounces differ by 9.7%: 1 troy oz = 31.1034768 / 28.349523125 ≈ 1.0971 avoirdupois oz. Common confusion: a "1 oz gold coin" weighs 31.1 g, not 28.3 g; conversely a "16 oz package" of food (1 lb avoirdupois) = 453.6 g, NOT 16 × 31.1 = 497.7 g. If the context is food, postage, or general retail, assume avoirdupois; if precious metals or pharmacy, assume troy.
Why is "fluid ounce" different from a regular ounce?
They measure different things: the avoirdupois ounce is mass (weight), and the fluid ounce is volume. The two share the name only because historically a fluid ounce of water at room temperature weighed roughly one avoirdupois ounce — a convenient approximation, not a definition. Modern values: 1 US fluid ounce = 29.5735295625 mL (1/128 of a US gallon = 1/128 × 3.785411784 L); 1 UK Imperial fluid ounce = 28.4130625 mL (1/160 of an imperial gallon = 1/160 × 4.54609 L). Recipe pitfall: "4 oz butter" = 113.4 g (mass; cooking ingredient); "4 fl oz milk" = 118.3 mL US (volume; cooking ingredient). When in doubt: liquids (water, milk, oil) → fluid ounces (volume); solids (butter, flour, meat) → avoirdupois ounces (mass). US recipes often drop the "fl" abbreviation for liquids — context tells you which.
What are common cooking weight references for ounces?
Quick reference table for US recipe conversion: 1 oz = 28.35 g · 2 oz = 56.70 g · 4 oz = 113.40 g (1 stick US butter, ¼ lb) · 6 oz = 170.10 g · 8 oz = 226.80 g (½ lb; common cheese block size) · 12 oz = 340.19 g (¾ lb) · 16 oz = 453.59 g (1 lb; standard ground-meat tray). 1 large egg ~50 g ≈ 1.76 oz. 1 cup butter (½ lb) = 226.80 g. 1 cup white sugar ≈ 200 g. The FDA Nutrition Facts label (21 CFR 101.9) declares serving sizes in g for solids and mL for liquids; the "oz" appearing on US food packaging is almost always the avoirdupois weight ounce, except on alcoholic beverages where US labels use fluid ounces (volume). For postage, USPS First-Class Mail rates step up at 1, 2, 3, … 13 oz before transitioning to flat-rate parcel pricing.
How is the avoirdupois ounce derived historically?
The avoirdupois system traces to the medieval Anglo-French wool trade (avoir-de-pois, "goods of weight") in the 14th-15th centuries, replacing the tower pound (~350 g) that earlier Plantagenet England had used. The base unit of the system is the grain (~64.79891 mg, originally a barley grain), with 16 ounces per pound and 7000 grains per pound. Compare the troy system (5760 grains per troy pound, 12 troy oz of 480 grains each) which retained the older Roman unciae structure. The 1959 IYPA fixed the avoirdupois pound at exactly 7000 × 0.06479891 g = 453.59237 g = 0.45359237 kg, anchoring the grain by definition. Modern usage retains avoirdupois for everyday US weighing (food, postage, retail packaging) and continues troy for precious metals and apothecary contexts; the metric kilogram (SI base unit since the 1875 Convention du Mètre, redefined via Planck constant in 2019) superseded both for scientific work.
Sources (6)
- U.S. National Bureau of Standards (1959). Refinement of Values for the Yard and the Pound — International Yard and Pound Agreement (1 lb avoirdupois = exactly 0.45359237 kg → 1 oz avoirdupois = 1/16 lb = 28.349523125 g exactly). Federal Register Doc 59-5442, published 30 June 1959, effective 1 July 1959 (joint declaration with the United Kingdom, Australia, Canada, New Zealand, and South Africa).
- Thompson, A., & Taylor, B. N. (2008). Guide for the Use of the International System of Units (SI) — NIST Special Publication 811, 2008 edition; codifies the international avoirdupois ounce factor for U.S. usage. U.S. National Institute of Standards and Technology (NIST), Gaithersburg, MD — physics.nist.gov/cuu/pdf/sp811.pdf.
- UK Parliament (1985). Weights and Measures Act 1985, Schedule 1 — pound defined as 0.45359237 kg, ounce as 1/16 of pound (28.349523125 g). UK statute (legislation.gov.uk); aligns the United Kingdom with the 1959 International Yard and Pound Agreement.
- Verdict of the Trial of the Pyx, 18 Henry VIII / British Royal Mint Museum historical record (1527). Troy ounce adopted as Britain's legal standard for gold and silver — 12 troy oz per troy pound; 1 troy oz ≈ 31.1034768 g (vs avoirdupois 28.349523125 g, a 9.7% difference); the troy system remains the precious-metals quotation standard. Verdict of the Trial of the Pyx, 18 Henry VIII (parchment roll, Chapter House, Westminster, 1527), preceded by royal proclamation 5 November 1526; US Mint formalized troy-pound standard at Philadelphia in 1828.
- U.S. Code of Federal Regulations (1993). 21 CFR 101.9 — Nutrition labeling of food (FDA): codifies the avoirdupois-vs-fluid-ounce distinction in food labelling. Serving sizes for liquids are declared in mL/fl oz (volume), for solids in g/oz (mass). 1 US fl oz = 29.5735295625 mL = 1/128 US gallon = 1/128 × 3.785411784 L exact. U.S. Food and Drug Administration; 21 CFR 101.9 implemented under the Nutrition Labeling and Education Act 1990 (Public Law 101-535) via final rule published 6 January 1993 (58 FR 2079), effective 8 May 1994.
- World Wide Web Consortium (W3C) (2018). Web Content Accessibility Guidelines (WCAG) 2.1 — Success Criterion 4.1.3 Status Messages. W3C Recommendation 5 June 2018; carried unchanged into WCAG 2.2 (Recommendation 5 October 2023).
These are the original publications the formulas in this tool are based on. Locate them by journal name and year on Google Scholar or PubMed.
By Marco B. ·