Convert Mass from Kilogram to Gram (kg to g)
Multiple conversions

Kilogram to Gram Conversion Formula

To convert from Kilogram (kg) to Gram (g), use the following formula:

Example

Let's convert 5 Kilogram (kg) to Gram (g).

Using the formula:

Therefore, 5 Kilogram (kg) is equal to $5000$ Gram (g).

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 a Gram (g)?

A gram (g) is a base unit of mass in the metric system. The plural form is grams.

Where Did the Gram Originally Come From?

The gram was initially defined in 1795 by the French National Convention.

Its first definition was based on the mass of one cubic centimeter of pure water at the temperature of its maximum density, which is approximately 4 degrees Celsius (4 °C).

This practical, water-based definition was a revolutionary step toward a standardized and universal system of measurement, moving away from the inconsistent and often confusing units of time.

Grams vs. Ounces: What's the Difference?

A gram is much smaller than an ounce, the standard unit of mass in the imperial and US customary systems.

One ounce equals approximately 28.35 grams, which is why grams are preferred for scientific work and for measuring small amounts, such as spices or medicine.

The metric system's decimal structure (for example, 1,000 grams in a kilogram) also makes calculations simpler than in the imperial system.

How Is the Gram Defined Today?

Although the gram was once tied to water, it's no longer linked to any physical object.

Since 2019, the kilogram — and therefore the gram — is defined by a fundamental constant, the Planck constant (h).

That shift makes the unit stable and reproducible in any properly equipped laboratory, without relying on the old International Prototype of the Kilogram.

What is the metric system?

Kilogram to Gram Conversion Table

Here are some quick reference conversions from Kilogram (kg) to Gram (g):