# kilogram per square metre

##### SI coherent derived unit
Name Symbol Derived quantity
kilogram per
square metre
kg m−2 surface density

### Definition

The kilogram per square metre, symbol kg m−2, is the SI coherent derived unit of surface density.

An area of one square metre with a mass of one kilogram has a surface density of one kilogram per square metre.

### Paper

The surface density of paper is measured in units of grams per square metre, symbol g/m2.

### Body mass index

Body mass index (BMI) is defined as body mass divided by the square of body height. BMI is expressed in units of kg/m2, although in common use the units are generally omitted.