Skip to content
CalcTheBuild

Paint Calculator

Stop guessing at the paint counter. Enter your room size, the number of doors and windows and the coats you plan to apply, and we'll tell you how much paint to buy and roughly what it will cost.

ft
ft
ft
sq ft/gal

Check the can. Typical: 350–400 sq ft/gal or 10–12 m²/L.

$/gal

Your estimate

Paint needed
2.08 gal
Gallon cans to buy
3 gallons
Paintable area (one coat)
364.87 sq ft
Total area incl. all coats
729.74 sq ft
Estimated paint cost
$135.00

Doors counted as 21 sq ft (1.95 m²), windows as 15 sq ft (1.4 m²).

How to use this calculator

  1. Enter the room's length, width and wall height.
  2. Count the doors and windows. We subtract a standard area for each.
  3. Choose whether you're painting the ceiling too.
  4. Choose the number of coats. Two is standard, and three helps when changing from a dark colour to a light one.
  5. Check the coverage figure on the can and enter it.

How paint quantity is calculated

Wall area is the room perimeter × height, minus 21 sq ft (1.95 m²) per door and 15 sq ft (1.4 m²) per window. Multiply by the number of coats and divide by the paint's coverage to get the volume needed.

We round up to whole gallon cans in imperial mode and to 2.5 L tins in metric mode, because that's how paint is usually sold.

Pro tips

  • Use a primer on new drywall or when making big colour changes. It often saves a finish coat.
  • Textured or porous surfaces can use 20–30% more paint than the label suggests.
  • Mix all your cans in a bucket before you start (called boxing) so the colour is even across the room.

Frequently asked questions

How much paint do I need for a 12×12 room?

A 12 × 12 ft room with 8 ft walls, one door and two windows has about 333 sq ft of wall. Two coats at 350 sq ft per gallon need about 1.9 gallons, so buy 2 gallons.

How many square feet does a gallon of paint cover?

Most interior paints cover 350–400 sq ft per gallon per coat on smooth, primed walls. In metric, that's about 10–12 m² per litre.

Do I really need two coats of paint?

Usually, yes. Two coats give even colour and sheen and a more durable finish. Some paint-and-primer products can cover in one coat when you're repainting a similar colour.

These results are estimates for planning and budgeting. Actual quantities depend on site conditions, products and workmanship. Check structural and code requirements with a licensed professional before you build.