What is the difference between a 120×200 and a 140×200 mattress?

A standard single mattress measures 90×200 cm, a 120×200 already gives you 30 centimetres of extra width. A 140×200 adds another 20 centimetres and is the smallest true double size. Choose 120×200 if you sleep alone in a compact space; choose 140×200 if you occasionally share the bed or simply want more room to stretch out.