Arrange the following lengths in their increasing magnitude: 1 metre, 1 centimetre, 1 kilometre, 1 millimetre.

Arranging the lengths in increasing magnitude:

1. 1 millimetre (1 mm): The smallest unit among the given lengths.
2. 1 centimetre (1 cm): Next larger unit, consisting of 10 millimetres.
3. 1 metre (1 m): Greater than centimetre, comprising 100 centimetres.
4. 1 kilometre (1 km): The largest unit, equivalent to 1000 metres.