To measure your bathroom area
For square meters measure length
by breath e.g.

1000 mm x 1200 mm = 1.2 m2
Or 1500 mm x 1300 mm = 1.95 m2

For lineal meters measure all junctions
where wall meet with floors etc.

If floor is 1200 mm long and the wall height
is 1800 mm total lineal meters is
3ooo mm or 3 meters