Paint calculator
Work out how many gallons of wall and ceiling paint a room or a whole house needs, with doors and windows taken off.
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Your rooms
How the paint amount is worked out
The wall area of a room is its perimeter (twice the length plus twice the width) times the ceiling height. Each door and window is then taken off: a standard 3' × 6'8" door is about 20 sq ft and a 3' × 4' window about 12 sq ft.
The paintable area is multiplied by the number of coats and divided by what one gallon covers. Most interior paints cover about 350 sq ft per gallon per coat, and 2 coats is the usual recommendation, especially over a new or different colour. Check the can and change the coverage if yours says otherwise.
Walls and ceiling are worked out separately and each is rounded up to whole gallons, because they are usually different paints. Leave the ceiling off if you are only painting walls.
vPlan AR uses the same method for a scanned or drawn plan, measuring each wall face on the inside of the room and taking off the actual doors and windows.
Tips
- Primer over bare drywall or a big colour change counts as a coat of its own: buy it separately.
- Textured or porous walls take more paint; lower the coverage to around 250–300 sq ft per gallon.
- Keep a quart of each colour for touch-ups.
- Metric: one US gallon is about 3.8 litres, so the result is also shown in litres.
Do this from a scan instead
Scan the room or draw it, and vPlan AR measures every wall face on the inside of the room, takes off each door, window and cased opening, and lists the gallons per colour across the whole plan.
Frequently asked questions
How much paint do I need for a 12×12 room?
With 8' ceilings, one door and two windows, the walls are 384 sq ft less about 44 sq ft of openings, so about 340 sq ft. At 2 coats and 350 sq ft per gallon that is just under 2 gallons for the walls, plus 1 gallon for the 144 sq ft ceiling.
How many coats of paint do I need?
Two coats is the usual recommendation for even colour and durability. One coat can be enough when repainting the same colour; a dark colour over light, or bare drywall, may need primer first.
Do I subtract doors and windows when calculating paint?
Yes. A standard interior door is about 20 sq ft and a typical window about 12 sq ft. The calculator takes them off for you when you enter how many each room has.
How much area does a gallon of paint cover?
Most interior wall paints say about 350–400 sq ft per gallon for one coat on a smooth wall. The calculator uses 350 by default; change it to match your paint.
Guides
- How to Work Out Flooring, Paint and Baseboard Quantities from a Floor PlanFlooring needs waste for its pattern, paint needs the doors and windows taken off each wall, and baseboard stops at every doorway. Here is how to work out all three from a floor plan, by hand and in vPlan AR.
- How to Present Interior Design Options to Clients and Get Sign-Off Room by RoomClients decide faster when every room shows its finishes, its board and how it looks in the actual space, with no more than a couple of options and a clear way to say yes. Here is how to build that presentation, and how to do it in vPlan AR.