What are the main SI units for length, mass, and time?

In one line

The rule

In the International System of Units (SI), the standard unit of length is the metre (m), for mass is the kilogram (kg), and for time is the second (s).

Let's understand it simply

Imagine you are measuring how long your cricket bat is, how heavy your school bag is, or how long it takes to boil milk. The world uses the same set of units so everyone understands the measurement. These are called SI units. For length, we use metre (m). For mass, we use kilogram (kg). For time, we use second (s).

Remember it

Think: "M-K-S" — Metre, Kilogram, Second — the three main SI units.