milligram (mg)

What is milligram?

A milligram is a metric unit of mass equal to one thousandth of a gram. It is commonly used in pharmaceutical dosing, nutritional content labelling, and laboratory chemistry.

Notes: Metric unit

Real-world uses

Milligrams are the standard unit for pharmaceutical dosages (e.g., 500 mg ibuprofen), nutritional supplement quantities, and blood test results such as cholesterol levels (mg/dL). Environmental scientists measure pollutant concentrations in mg/L.

History

The milligram was established with the metric system's prefix conventions in the 1790s. Its importance grew dramatically with modern pharmacology, where precise small-mass measurements became critical for drug safety and efficacy.

Common mistakes

Confusing milligrams with micrograms—a factor-of-1000 error that can be dangerous in medication dosing. The abbreviation "mcg" is sometimes used for micrograms to avoid confusion with "mg."

When is this conversion used?

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.

How to convert milligram to kilogram

To convert milligram to kilogram, multiply the value by 0.000001.

Conversion formula (from base unit)

x * 0.000001

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.

Common values

Full milligram conversion table

Other Mass units

View all Mass conversions

• kilogram
• gram
• pound
• ounce
• tonne
• microgram
• stone
• short ton (US)
• long ton (UK)