What is ounce?
An ounce is a unit of mass in imperial and US customary systems equal to approximately 28.35 grams. It is frequently used in cooking, food portioning, and the measurement of precious metals.
Real-world uses
Ounces are used in the US and UK for food packaging, postal weights, and cooking recipes. Precious metals are weighed in troy ounces (slightly heavier than avoirdupois ounces) on commodity exchanges worldwide.
History
The word "ounce" comes from the Latin "uncia," meaning one-twelfth (of a Roman pound). The avoirdupois ounce became standard in English trade by the 14th century, defined as 1/16 of an avoirdupois pound.
Common mistakes
Confusing avoirdupois ounces (28.35 g, used for general weight) with troy ounces (31.10 g, used for precious metals) or fluid ounces (a volume measure). These are three distinct units sharing the name "ounce."
What is kilogram?
The kilogram is the SI base unit of mass. It is used globally as the standard for measuring weight and mass in science, industry, trade, and everyday life.
Real-world uses
The kilogram is the SI base unit of mass, used universally in science, commerce, and daily life outside the US. Grocery items, body weight in medical settings, and shipping weights are measured in kilograms across most of the world.
History
Originally defined in 1795 as the mass of one litre of water at 4°C. A platinum-iridium cylinder served as the standard from 1889 until 2019, when the kilogram was redefined in terms of the Planck constant, ending reliance on a physical artefact.
Common mistakes
Confusing mass (kg) with weight (newtons)—a kilogram measures mass, not force. Also, assuming 1 kg equals exactly 2 pounds; it is actually about 2.205 pounds.
When is this conversion used?
Converting between ounce and kilogram is common when working across metric and imperial systems, such as international trade, travel between countries with different measurement standards, or following instructions from a different region. Body weight, grocery items, and luggage limits are commonly expressed in kilograms in most countries and pounds in the US and UK, making this one of the most frequently needed mass conversions. Cooking recipes and food packaging often switch between grams and ounces, especially when adapting recipes from different culinary traditions.
Worked examples
1 ounce = 0.02834952 kilogram
1 kilogram = 1 kilogram
How to convert ounce to kilogram
To convert ounce to kilogram, multiply the value by 0.02834952.
To convert kilogram back to ounce, multiply by 35.27396195.
Measurement standards
The kilogram is defined by fixing the Planck constant to exactly 6.62607015 × 10⁻³⁴ joule-seconds, as established at the 26th General Conference on Weights and Measures in 2018. This ended the last SI definition based on a physical artefact.
Did you know?
The International Prototype of the Kilogram, a platinum-iridium cylinder stored near Paris since 1889, was found to have drifted by about 50 micrograms relative to its copies over a century — roughly the mass of a fingerprint.
Quick reference: ounce to kilogram
| ounce | kilogram |
|---|---|
| 0.1 | 0.00283495 |
| 0.5 | 0.01417476 |
| 1 | 0.02834952 |
| 2 | 0.05669905 |
| 5 | 0.14174762 |
| 10 | 0.28349523 |
| 25 | 0.70873808 |
| 50 | 1.41747616 |
| 100 | 2.83495231 |
| 250 | 7.08738078 |
| 500 | 14.17476156 |
| 1,000 | 28.34952313 |
Common values
| ounce | kilogram | |
|---|---|---|
| A paperclip | 35.27396195 ounce | 1 kilogram |
| A smartphone | 6,172.94334118 ounce | 175 kilogram |
| A bag of sugar | 35.27396195 ounce | 1 kilogram |
| Average adult human | 2,469.17733647 ounce | 70 kilogram |
| A small car | 42,328.7543395 ounce | 1,200 kilogram |