Ounces to Kg Converter

An ounce is a US customary unit of weight, and a kilogram is the base unit of mass in the metric system. Converting between them takes one exact number, so the answer is never an estimate. This tool uses the avoirdupois ounce by default, the everyday ounce on kitchen scales, baby scales and postal scales, and has a troy ounce option for gold and silver.

What Ounces to Kilograms Conversion Measures

This tool changes the unit, not the weight. 120 ounces, 7 lb 8 oz and 3.4019 kg are one weight written three ways. It is built for amounts that scales show in ounces, such as a newborn, a block of cheese or a parcel. USPS Ground Advantage retail prices under one pound are set in ounce steps of 4, 8, 12 and 15.999 oz, then move to whole pounds³. It converts weight ounces only. Fluid ounces measure volume and need a different tool.

The Formula

The pound is exactly 453.59237 grams and holds 16 ounces, so one avoirdupois ounce is exactly 28.349523125 grams, or 0.028349523125 kg¹. The pound took this value after English-speaking nations agreed in 1958 to unify their standards of mass and length, with the new factors announced in 1959².

Kilograms = ounces x 0.028349523125

Grams = ounces x 28.349523125

Total ounces = (pounds x 16) + ounces

How This Calculator Computes Your Result

Choose Ounces or Pounds and ounces, then type a weight. Decimals are fine, and you can paste text like 7 lb 8 oz. Nothing is rounded until the last step. Kilograms show to 4 decimals and grams to 1 decimal. For a pounds and ounces line, total ounces are rounded to 1 decimal first (2 decimals under 1 oz) and then split, so 15.999 oz reads 1 lb 0.0 oz and never 0 lb 16.0 oz. An ounces field of 16 or more rolls into pounds. A troy ounce option and a swap button are included. Swap flips the tool to kilograms in, ounces out.

What Your Result Means

Your result is the same weight in metric units. Use these tables to check your answer.

A quick check: divide the ounces by 35 for a rough kilogram figure. It runs about 0.8 percent high.

Troy Ounces Are Not Everyday Ounces

Gold and silver bars use a different ounce. The troy ounce is 480 grains, or 31.1034768 g, while the avoirdupois ounce is 437.5 grains, or 28.349523125 g¹. That makes a troy ounce about 9.7 percent heavier. London gold bars are weighed in troy ounces, and a typical bar is about 400 troy ounces, roughly 12.5 kg⁴. Converted exactly, 400 troy ounces is 12.441 kg. Treated as everyday ounces, it would come out as 11.340 kg, over a kilogram short. If a jewelry or bullion listing says "ounce", check which one it means.

Weight Ounces Are Not Fluid Ounces

NIST Handbook 44 defines the fluid ounce as a unit of volume, and its notes say to name the avoirdupois ounce and the fluid ounce clearly so the two are not mixed up¹. A fluid ounce of oil and a fluid ounce of honey fill the same space but do not weigh the same, so a volume cannot become kilograms without the density. Food guides add a third meaning. In USDA MyPlate, an ounce-equivalent is a serving unit, such as one slice of bread, and is not a weight⁵. This converter reads only weight ounces.

Birth Weight in Pounds and Ounces

US families usually hear a newborn's weight in pounds and ounces, and a 7 lb 8 oz baby weighs 3.4019 kg. The World Health Organization publishes weight-for-age percentile tables built from its child growth standards. At birth, they list these values⁶:

A percentile shows where a weight sits among a reference group. The 50th is the middle value. The WHO tables are printed to 0.1 kg, so the pound figures are close, not precise. These numbers do not say whether any baby is healthy. To compare a child's weight and height over time, see the Child Growth Percentile Calculator.