How to measure a room for paint
A reliable paint estimate starts with surface area rather than floor area.
Measure the perimeter
Add the lengths of every wall that will be painted. Irregular rooms can be split into smaller wall sections.
Subtract openings
Measure doors, windows and other large areas that will not receive paint, then subtract them from the wall total.
Keep units consistent
Use metres throughout if your coverage figure is in square metres per litre.