What is the standard SI unit for mass?

The story behind the answer

Kilogram is the SI base unit of mass. While gram is commonly used, it’s actually a derived unit (1 g = 0.001 kg). Tonne (metric ton) equals 1000 kg and is accepted for use with SI but isn’t a base unit, and pound belongs to the imperial system. Mass (kilogram) measures how much matter something has; weight is the force on that mass and depends on gravity.

Since 2019, the kilogram is defined by fixing the value of the Planck constant and realized with a Kibble balance, replacing the old metal reference cylinder. Memory tip: “Kilo-gram is the king of mass”—the only SI base unit that already contains a prefix—so all other mass units in SI (like grams and tonnes) relate back to it.