A reliable paint plan begins with a small set of measurements written down room by room. Measuring the perimeter is faster and less error-prone than treating every wall as a separate project.
Measure the room shell
Measure the length and width at floor level, then measure wall height from finished floor to ceiling. Older rooms can vary, so use the tallest height when you want a conservative estimate.
- Sketch the room and label length and width.
- Measure the wall height.
- Record any half walls, alcoves, or sections with a different height separately.
Record openings
Measure each door and window as width × height. Subtract only openings that will not be painted. A closet door, built-in cabinet, or large fireplace can be treated the same way.
- Count repeated opening sizes.
- Keep trim separate if it uses another product.
- Do not subtract tiny outlets or switch plates; their area is negligible.
Audit the result
The four-wall area for a rectangular room is 2 × (length + width) × height. Add length × width for a painted ceiling, then subtract openings. Compare that result with your notes before selecting coats and coverage.
Practical takeaway
Keep one line per room. A room-by-room plan is easier to revise, save, share, and shop from than one unexplained total.
Related paint guides
How much paint does a gallon cover?
Understand label coverage, surface porosity, colour changes, and why exact paint volume differs from cans to buy.
Do I need one coat or two?
Choose a realistic coat count based on colour change, surface condition, sheen, and product instructions.
How to subtract doors and windows
Decide which openings are worth subtracting and keep trim calculations separate.