Convert Mass from Ounce to Kilogram (oz to kg)

Ounce to Kilogram Conversion Formula

To convert from Ounce (oz) to Kilogram (kg), use the following formula:

With $453.59237$ is the ratio between the base units Gram (g) and Pound (lb).

Example

Let's convert 5 Ounce (oz) to Kilogram (kg).

Using the formula:

Therefore, 5 Ounce (oz) is equal to $0.141747615625$ Kilogram (kg).

What is an Ounce (oz)?

An ounce (oz) is a unit of mass in the imperial system, equal to 0.0625 (or 1/16) Pounds (lb).

What's the Difference Between a Troy Ounce and a Standard Ounce?

While most people are familiar with the standard ounce used for groceries, there is another crucial measurement called the Troy Ounce.

The standard ounce, officially known as the Avoirdupois ounce, is approximately 28.35 grams and is used for weighing everyday items.

The Troy ounce, however, is slightly heavier, at approximately 31.1 grams, and is the universal standard for measuring precious metals, such as gold, silver, and platinum. This distinction is vital in the jewelry and investment markets.

Ounce vs. Fluid Ounce: Are They the Same?

A common point of confusion is the difference between an ounce (oz) and a fluid ounce (fl oz).

An ounce is a unit of mass (weight), while a fluid ounce is a unit of volume.

For example, you would use ounces to weigh a block of cheese but fluid ounces to measure a glass of milk. The weight of one fluid ounce of a liquid depends entirely on its density; one fluid ounce of honey, for instance, weighs more than one fluid ounce of water.

Where Did the Ounce Come From?

The word "ounce" comes from the Latin uncia.

In ancient Rome, an uncia was one-twelfth of a libra (the Roman pound), and that system helped shape many European measures.

Today's avoirdupois ounce is one-sixteenth of a pound. However, the name still preserves a direct link to Rome's old system of weights and measures.

What is a Kilogram (kg)?

A kilogram (kg) is the base unit of mass in the metric system, used worldwide to measure everything from your body weight to the groceries you buy.

It's equal to 1,000 grams (g).

For a simple real-world comparison, the mass of a one-liter bottle of water is almost exactly one kilogram.

Key Takeaways

• A kilogram is 1,000 grams.
• The kilogram is now defined by the Planck constant, a fundamental constant of nature.
• Previously, it was defined by a physical metal cylinder in France named "Le Grand K."
• It is the only SI base unit that has a prefix ("kilo") in its name.

How Is the Kilogram Defined Today? From an Object to a Constant

For more than 130 years, the kilogram was a physical object: a platinum-iridium cylinder called the International Prototype Kilogram (IPK), also known as "Le Grand K," which was kept under tight security near Paris.

Scientists eventually found the problem — the artifact was losing an imperceptible amount of mass over time — so it couldn't guarantee the long-term accuracy required by science and industry.

On May 20, 2019, the kilogram was redefined.

It's no longer tied to a single object but to a fundamental constant of nature: the Planck constant (h). That change makes the kilogram stable and reproducible with precision anywhere in the universe.

What Was the Original Definition of the Kilogram?

The kilogram's story begins during the French Revolution with the creation of the metric system. The original definition, established in 1795, was beautifully simple and practical.

The gram was first defined as the mass of one cubic centimeter of water at 4 °C (39.2 °F), the temperature at which it is most dense.

From there, the kilogram was defined as the mass of one liter (one cubic decimeter) of water under the same conditions. This practical, water-based definition was a revolutionary step toward a global standard of measurement.

Why Is the Kilogram a Unique SI Base Unit?

The International System of Units (SI) is built on seven base units that serve as the foundation for all measurements. These include the meter for length, the second for time, and the ampere for electric current.

The kilogram is a historical oddity, as it's the only SI base unit with a prefix ("kilo").

Due to its origins, the kilogram, rather than the gram, became the fundamental unit of mass, making it a curious exception in the measurement system.

What is the imperial system?

What is the metric system?

Ounce to Kilogram Conversion Table

Here are some quick reference conversions from Ounce (oz) to Kilogram (kg):