Paint Calculator
Planning a painting project? Our paint calculator takes the guesswork out of how much paint you need. Simply enter your room dimensions, the number of doors and windows, and how many coats you plan to apply. The calculator instantly shows the total paintable surface area and the exact volume of paint required — in either gallons or litres, depending on your preferred units.
Room Dimensions
Openings & Coats
Wall area
384 sq ft
Ceiling (not included)
—
Paintable area
333 sq ft
Paint needed
1.67 gallons
2 coats
Estimated Paint Required
1.67 gallons
Buy 10-15% extra for touch-ups
This calculator provides an estimate based on standard paint coverage rates. Actual coverage varies by surface texture, paint brand, and application method. Always verify coverage on your paint can label.
Planning a painting project? Our paint calculator takes the guesswork out of how much paint you need. Simply enter your room dimensions, the number of doors and windows, and how many coats you plan to apply. The calculator instantly shows the total paintable surface area and the exact volume of paint required — in either gallons or litres, depending on your preferred units.
How to Use This Calculator
- 1.Enter the length, width, and height of your room in feet (imperial) or metres (metric).
- 2.Input the number of doors and windows — the calculator subtracts their standard area from the total wall surface.
- 3.Choose whether to include the ceiling in your calculation.
- 4.Set the number of coats (2 is the standard recommendation for even coverage).
- 5.Read the results: total surface area, paintable area, and paint volume in gallons or litres.
How the Paint Calculator Works
The calculator follows a straightforward formula. First, it computes the total wall area: Wall Area = 2 × (Length + Width) × Height. If you include the ceiling, it adds Ceiling Area = Length × Width. Then it subtracts the area of doors (21 sq ft / 1.95 sq m each) and windows (15 sq ft / 1.4 sq m each). The result is the paintable surface area. Finally, it divides by the paint coverage rate — approximately 400 sq ft per gallon or 10 sq m per litre for smooth interior walls — and multiplies by the number of coats: Paint Volume = (Paintable Area × Coats) ÷ Coverage Rate.
Frequently Asked Questions
How much paint do I need for a 12×12 room?
A 12×12 room with 8-foot ceilings has approximately 384 sq ft of wall area (2 × (12 + 12) × 8). After subtracting one door (21 sq ft) and two windows (30 sq ft), the paintable area is about 333 sq ft. At 400 sq ft per gallon with 2 coats, you need roughly 1.7 gallons — about 2 gallons to account for touch-ups.
How many coats of paint should I apply?
Two coats is the industry standard for most interior painting. One coat may suffice if you are repainting with the same colour, but two coats ensure even coverage, better durability, and true colour accuracy, especially when painting over a darker shade.
Does this paint calculator account for doors and windows?
Yes. The calculator subtracts 21 sq ft (1.95 sq m) per door and 15 sq ft (1.4 sq m) per window from the total wall area, giving you the actual paintable surface and a more accurate paint estimate.
Should I include the ceiling in my paint calculation?
Only if you plan to paint the ceiling. The calculator lets you toggle ceiling inclusion on or off. Ceiling paint is typically a separate product (flat finish, often white), so calculating it separately helps you buy the right type and quantity.
Last updated: 2026-10-06
Disclaimer: This calculator provides an estimate based on standard paint coverage rates. Actual coverage varies by surface texture, paint brand, application method, and environmental conditions. Always buy 10-15% extra paint for touch-ups and re-verify coverage rates on your paint can label.