An avoirdupois ounce is 1/16 pound.
Ounces to Kilograms Converter — oz to kg
Convert Ounce (oz) to Kilogram (kg) using the exact conversion factor (1 ounce = 0.0283495231 kilogram). See the formula, worked examples, conversion table, unit comparison, history, and common uses.
Ounces to Kilograms converter
Converter
Mass/Weight Converter
Convert SI mass, imperial weight, jewelry, atomic, and astronomy mass units.
Context values
Some unit families need one extra value for a physically accurate result.
Kilogram is 1000 gram units.
Result = input x 0.02834952313 / 1.
Mass uses the kilogram as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Ounces to Kilograms
Weight conversions between Ounce and Kilogram come up constantly in everyday commerce, shipping, and cooking, since US packaging is usually labeled in pounds while most of the rest of the world uses kilograms. Ounce is typically associated with united States (cooking, postal, retail), while Kilogram is typically associated with used as the standard mass unit in nearly every country except the United States and a few others that primarily use the pound..
Formula
kilograms = ounces × 0.028349523125
This factor comes from each unit's defined relationship to the category's base unit: 1 ounce equals 0.028349523125 base units, and 1 kilogram equals 1 base unit, so dividing one by the other gives the direct ounce-to-kilogram factor of 0.028349523125.
Simple example
1 oz × 0.02834952313 = 0.0283495231 kg
1 ounce = 0.0283495231 kilograms.
Real-world example
50 oz × 0.02834952313 = 1.417476156 kg
50 ounces = 1.417476156 kilograms.
Conversion table
| Ounce (oz) | Kilogram (kg) |
|---|---|
| 1 oz | 0.0283495231 kg |
| 5 oz | 0.1417476156 kg |
| 10 oz | 0.2834952313 kg |
| 25 oz | 0.7087380781 kg |
| 50 oz | 1.417476156 kg |
| 100 oz | 2.834952313 kg |
Reverse conversion: Kilogram to Ounce
0.0283495231 kg × 35.27396195 = 0.9999999991 oz
0.0283495231 kilograms = 0.9999999991 ounces.
ounces = kilograms × 35.2739619496
For a page dedicated to this direction, see Kilogram to Ounce.
Ounce vs. Kilogram
| Aspect | Ounce | Kilogram |
|---|---|---|
| Family | US/imperial customary unit | SI base unit |
| Typical use | US cooking and recipe measurement (small quantities) | Pricing and labeling goods sold by weight in retail and commodity trade |
| Where it's used | United States (cooking, postal, retail) | Used as the standard mass unit in nearly every country except the United States and a few others that primarily use the pound. |
Understanding the Ounce
Ounce (oz) measures mass. The avoirdupois ounce is 1/16 of a pound: exactly 28.349523125 grams. It is classified as a US/imperial customary unit.
Where it's used: United States (cooking, postal, retail) United Kingdom (informal/retail use)
Avoirdupois ounce vs. troy ounce. The everyday ounce (avoirdupois, 28.35 g) used for cooking and shipping is a different, smaller unit than the troy ounce (31.10 g) used for precious metals like gold and silver — this page uses the everyday avoirdupois ounce.
Uses of the Ounce today
- US cooking and recipe measurement (small quantities)
- US postal and shipping weight
- Precious metals (troy ounce, a related but distinct unit)
History of the Ounce
The ounce descends from the Roman 'uncia' (a twelfth part), inherited through medieval English weight systems; the avoirdupois ounce (for general goods, as opposed to the troy ounce for precious metals) became standard for everyday trade, fixed at exactly 28.349523125 g via the pound's 1959 international standardization.
Historical origin. Ounce was not the invention of a single named person; it developed through the process described above.
Understanding the Kilogram
Kilogram (kg) measures mass. The kilogram is the SI base unit of mass; every other SI mass unit is a decimal multiple or fraction of it. It is classified as a SI base unit.
Where it's used: Used as the standard mass unit in nearly every country except the United States and a few others that primarily use the pound.
Uses of the Kilogram today
- Pricing and labeling goods sold by weight in retail and commodity trade
- Dosing calculations in medicine, especially for pediatric and weight-based prescriptions
- Structural and material specification in metric-system engineering
- Scientific measurement of mass across chemistry, physics, and materials research
History of the Kilogram
The kilogram's direct predecessor was the 'grave,' defined by the French Academy of Sciences in 1793 as the mass of one cubic decimeter of water at its temperature of maximum density. Because 'grave' echoed the aristocratic title 'graf,' revolutionary France's decree of 18 Germinal, Year III (7 April 1795) renamed the system: the gram became the reference unit, defined as the mass of one cubic centimeter of water at the melting point of ice, and the kilogram — one thousand grams — took over the grave's practical role.
Turning that water-based definition into a physical object required real experimental work: chemist Louis Lefèvre-Gineau was tasked in 1795 with measuring precisely how much a cubic decimeter of water weighed, and former royal jeweller Marc-Étienne Janety then fabricated a platinum cylinder to embody that measured mass. Deposited in the French National Archives in 1799, it became known as the Kilogramme des Archives.
The metric system spread unevenly — Napoleon briefly restricted its use — but France made it compulsory in 1840, and the 1875 Metre Convention (signed by seventeen nations including the US) established the BIPM and a shared international prototype. The platinum-iridium International Prototype of the Kilogram, adopted in 1889 and nicknamed 'Le Grand K,' served as the world's mass reference for over a century.
On 20 May 2019, the kilogram was redefined by fixing the Planck constant at exactly 6.62607015 × 10⁻³⁴ joule-seconds, so it can now be realized in a laboratory (via a Kibble balance) without reference to any physical object.
Historical origin. Kilogram was not the invention of a single named person; it developed through the process described above.
Ounce — sources
- NIST — International yard and pound (1959) — Basis for the modern ounce via the standardized pound.
Kilogram — sources
- BIPM — The kilogram (SI base unit) — Official definition and history since the 2019 redefinition.
- NIST — Kilogram: The Past — History of the kilogram standard from the grave to the International Prototype Kilogram.
- SI Brochure, 9th edition (2019), Appendix 2 — BIPM — Official text of the Planck-constant-based definition of the kilogram.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many kilograms are in 1 ounce?
1 ounce equals 0.0283495231 kilograms, using the exact defined conversion factor rather than an estimate.
How do I convert ounce to kilogram?
Multiply the ounce value by 0.02834952313. The converter above does this instantly to whatever precision you set.
How do I convert kilogram back to ounce?
Use the reverse factor: 1 kilogram equals 35.27396195 ounces. You can also use the swap control in the converter above to flip the direction instantly.
What is a ounce?
Ounce (oz) measures mass. The avoirdupois ounce is 1/16 of a pound: exactly 28.349523125 grams. It is classified as a US/imperial customary unit.
What is a kilogram?
Kilogram (kg) measures mass. The kilogram is the SI base unit of mass; every other SI mass unit is a decimal multiple or fraction of it. It is classified as a SI base unit.
Is the ounce to kilogram conversion exact?
Yes. The avoirdupois ounce is 1/16 of a pound: exactly 28.349523125 grams. That fixed definition is what the converter above uses, so any rounding you see is a display choice, not a limitation of the math.
What is the difference between avoirdupois ounce vs. troy ounce?
The everyday ounce (avoirdupois, 28.35 g) used for cooking and shipping is a different, smaller unit than the troy ounce (31.10 g) used for precious metals like gold and silver — this page uses the everyday avoirdupois ounce.
Where is the ounce still used today?
United States (cooking, postal, retail) United Kingdom (informal/retail use)