What is the SI unit of mass?

The SI unit of mass is the kilogram (kg).

Key Points

• The kilogram is the only SI base unit that still carries a prefix (“kilo”).
• 1 kilogram (kg) = 1000 grams (g).
• Smaller units: gram (g), milligram (mg).
• Larger units: tonne (t), where 1 tonne = 1000 kg.

In short: Mass is measured in kilograms (kg) in the SI system.