Grams to Ounces Calculator

Background.

A grams-to-ounces calculator solves a kitchen problem that comes up every time an imported ingredient or a translated recipe lists a weight in grams while the measuring cups and kitchen scale on the counter are calibrated in ounces. A 340 g bag of pasta, a 400 g can of tomatoes, or a European baking recipe calling for 250 g of flour all need the same conversion before a US cook can weigh out the right amount with an ounce-only scale.

The factor behind the conversion, 1 ounce = 28.349523125 grams, is not an approximation rounded for convenience — it is derived directly from the exact 1959 international definition of the avoirdupois pound (0.45359237 kg, divided by the 16 ounces in a pound), so it carries no measurement uncertainty of its own. A 340 g bag of pasta converts to exactly 11.9931470629 oz, just a hair under 12 oz — close enough that a cook eyeballing '12 oz' on a US-labeled box would be off by less than a gram in practice, but the exact figure matters more as quantities scale up in a recipe.

Because recipe weights often need to be scaled — doubled for a dinner party, halved for a single serving — this calculator keeps every step in arbitrary-precision decimal arithmetic rather than ordinary floating point, so repeated conversions and unit-scaling do not accumulate the small rounding drift that floating-point division can introduce.

What is grams to ounces calculator?

Grams and ounces both measure mass, but they belong to different systems: the gram is a decimal subdivision of the SI kilogram, while the avoirdupois ounce is a US customary unit equal to 1/16 of a pound. The two are linked through the same fixed constant that defines the pound: because 1 avoirdupois pound is exactly 0.45359237 kilograms (set by the 1959 international yard-and-pound agreement) and there are exactly 16 ounces in a pound, 1 ounce is exactly 0.45359237 ÷ 16 = 28.349523125 grams. That value is a mathematical consequence of a legal definition, so it is exact to as many decimal places as you care to compute — there is no experimental uncertainty anywhere in the chain. This calculator converts grams to ounces by dividing the gram value by 28.349523125, giving a precise decimal-ounce figure suitable for a kitchen scale, a nutrition label cross-check, or scaling a recipe written in metric units.

How to use this calculator.

1. 01Enter the weight in grams — the default (340 g) is a common packaged-food net weight.
2. 02Read the result: the equivalent weight in ounces, computed to full decimal precision.
3. 03Round to the precision your kitchen scale supports (most digital scales read to the nearest 0.1 oz or 1 g).
4. 04Repeat for each ingredient in a metric recipe to build a full ounce-based shopping or measuring list.

The formula.

The calculator uses one fixed constant: 1 avoirdupois ounce equals exactly 28.349523125 grams. That number is not independently defined — it falls directly out of the 1959 international agreement that fixed the avoirdupois pound at exactly 0.45359237 kilograms, combined with the standard division of a pound into 16 ounces: 0.45359237 kg ÷ 16 = 0.028349523125 kg = 28.349523125 g. Because every input to that derivation is exact, the result is exact too.

To convert grams to ounces, the calculator divides the gram value by 28.349523125: ounces = grams ÷ 28.349523125. For the 340 g worked example, that division gives 11.9931470629 oz, computed with Decimal.js so the result holds ten decimal places of genuine precision rather than the rounding noise ordinary floating-point division would introduce at that scale. The same division applies uniformly whether the input is a single spice measurement in single-digit grams or a multi-kilogram bulk ingredient — there is no separate formula or lookup table involved.

A worked example.

Frequently asked questions.

References& sources.

1. [1]National Bureau of Standards (1959). Refinement of Values for the Yard and the Pound — establishes the international avoirdupois pound as exactly 0.45359237 kilograms, from which the ounce (1/16 lb = 28.349523125 g) is derived.
2. [2]National Institute of Standards and Technology (2008). NIST Special Publication 811: Guide for the Use of the International System of Units (SI), Appendix B — Conversion Factors.