What this result means
One avoirdupois ounce (oz) is exactly 28.349523125 grams (g). Divide grams by 28.349523125 to get ounces; multiply ounces by that value to get grams. This converter rounds the result once to two decimals. It uses mass ounces, not fluid or troy ounces. [1][2]
Where the exact factor comes from
The mass definitions in Schedule 1 give a pound as 0.45359237 kilogram and an ounce as one sixteenth of that pound. NIST lists 1,000 grams per kilogram. Therefore 0.45359237 Ă— 1,000 Ă· 16 = exactly 28.349523125 grams per ounce. [1][3]
NIST’s conversion table prints some factors to a limited number of significant digits. This tool uses the full factor derived from the unit definitions; the shortened table entry is a presentation of the same conversion, not a different ounce. [2]
Mass ounces, fluid ounces and troy ounces differ
NIST lists avoirdupois ounces, troy ounces and U.S. or Imperial fluid ounces separately. Avoirdupois and troy ounces measure mass with different factors; fluid ounces measure volume. A container marked in fluid ounces does not provide an ingredient mass by itself. [2]
Even if the ingredient is a liquid, use a measured gram mass for this tool. Converting a volume into grams requires information about density. This page does not assume that a milliliter weighs one gram or that all ingredients share a density.
An illustrative food-mass conversion
A measured 100 g ingredient portion gives 100 ÷ 28.349523125 = 3.527396… oz, displayed as 3.53 oz. In the other direction, 2 oz gives 56.69904625 g, displayed as 56.70 g. These examples illustrate arithmetic, rather than suggesting how much to eat.
Sixteen ounces gives exactly 453.59237 g before display rounding, matching the pound definition. The picture shows one mass expressed in two units around an unmarked kitchen scale. Its labels describe the definition, not a real scale reading. [1]
Do not add accuracy by adding decimals
The converter keeps the exact unit ratio during calculation and rounds only the output. For example, 0.141747615625 g is exactly 0.005 oz and displays as 0.01 oz because halfway ties round upward. A positive value below that threshold displays as less than 0.01 oz.
Converting 100 g to the rounded display 3.53 oz and converting that rounded number back gives 100.07 g. Rounding discarded detail in the first step. Keep the original measurement when accuracy matters; a longer calculator result cannot correct an uncertain kitchen scale.
Choose the direction before entering the number
Both directions accept values from 0 to 1,000,000 in the starting unit. These are software bounds, not dietary limits. Enter plain decimal-point numbers. Blank values, negatives, unit text, fractions, scientific notation, comma separators and nonfinite numbers are rejected. Changing the direction clears the previous entry to avoid mixing units.
The calculation runs in your browser without an account. Reset or reload clears the entries. Share uses the page address without input values or results. The optional recently-used list stores the tool identifier rather than the mass you entered.
Formula and assumptions
- Version
- International avoirdupois ounce and gram mass conversion, avoirdupois-ounce-exact-28-349523125-g-v1
- Rounding
- Use the exact fraction 226796185/8000000 for grams per ounce or its reciprocal; round once to two decimals with nonnegative halfway ties upward. Preserve the precision of the original measurement.
- Worked example
- For a measured 100 g ingredient mass: 100 ÷ 28.349523125 = 3.527396… oz, displayed as 3.53 oz. For 2 avoirdupois oz: 2 × 28.349523125 = 56.69904625 g, displayed as 56.70 g. The amount stays the same; only its unit changes.
Who this is for — and when not to use it
Intended use
Convert a known mass from grams to international avoirdupois ounces or back. Restate a measured food or ingredient mass in a different unit without changing its amount.
Not intended for
Convert fluid ounces, cups, milliliters or another volume into mass without measured density. Convert troy ounces or calculate precious-metal mass. Set food portions, nutrient intake, a supplement regimen or medicine doses.
Exclusions
- An unspecified ounce system, a volume-only quantity or unknown mass.
- Negative mass, unit text or values beyond the stated software bounds.
Evidence sources
- 1. Weights and Measures Act 1985: Schedule 1, mass definitions — UK legislation. Accessed Oct 11, 2026.
- 2. NIST Guide to the SI: Appendix B.8, conversion factors — National Institute of Standards and Technology. Accessed Oct 11, 2026.
- 3. SI Units: Mass — National Institute of Standards and Technology. Accessed Oct 11, 2026.