- Length is the distance from one point to another.
- The SI unit of length is a metre{m}.
- Other units of length are millimetres{mm}, centimetres{cm}, kilometres{km}.
- A ruler or a metre stick is used to measure the length of short straight lines.
- An opisometer is used to measure the length of short curved lines. For example, a road or a river on a map.
- A trundle wheel measures the length of long curved or straight lines. For example, the length of a room.
- A vernier calliper is used to measure diameters of solid objects. For example, a pipe.