Painting tool
Paint Calculator
Get gallons and cost in under a minute. Enter room dimensions, subtract doors and windows, and get a clean, practical estimate.
What this tool solves
- • Calculates exact paint gallons needed.
- • Subtracts doors and windows automatically.
- • Includes primer and ceiling options.
- • Estimates total material cost.
Enter room dimensions
Measure wall-to-wall interior dimensions.
Estimates only. Coverage varies by paint quality and surface.
Step 1: Room size
Step 2: Doors & windows
Step 3: Paint options
Paint estimate
Based on 2 coats at 350 sq ft per gallon (Eggshell / Satin), plus a 10% buffer.
3 gallons of paint
Calculated: 2.6 gallons (rounded up)
Selected finish: Eggshell / Satin
Estimated cost
Does not include brushes, rollers, tape, or drop cloths.
Visualize paint colors first?
Upload a room photo and see different wall colors with AI before you buy.
Try AI Room StylerPaint calculator FAQs
How much paint do I need for a 12x12 room?
A 12x12 room with 9ft ceilings has about 432 sq ft of wall space. After subtracting a door and two windows, you need roughly 1.5-2 gallons for two coats. Use the calculator above for exact amounts.
How many square feet does a gallon of paint cover?
One gallon of paint typically covers 350-400 square feet per coat. Coverage varies by paint quality, surface texture, and application method. This calculator uses 350 sq ft as a conservative estimate.
Do I need primer before painting?
Primer is recommended when painting over dark colors, new drywall, patched areas, or stained surfaces. Many modern paints include primer, but separate primer provides better coverage and adhesion.
Should I buy extra paint?
Yes, buy 10-15% more than calculated for touch-ups, mistakes, and future repairs. This calculator rounds up to whole gallons which typically provides this buffer.
Explore more tools
Plan your full room project with spacing, budgets, and palettes.
How much paint do I need?
One gallon of paint covers roughly 350–400 sq ft of wall area with a single coat. For most rooms, plan on 1–2 gallons for walls depending on room size, number of coats, and paint finish.
How many gallons for a 12×12 bedroom?
A 12×12 room with 9ft ceilings has roughly 288 sq ft of total wall area. After subtracting one door (~21 sq ft) and two windows (~42 sq ft), you're left with about 225 sq ft of paintable surface. With 2 coats and a 10% waste buffer, that's around 1.4 gallons, so two 1-gallon cans is the practical purchase.
1 coat vs 2 coats: does it matter?
Two coats is the standard for full, even coverage, especially when switching colors or painting over a dark shade. One coat can work for light touch-ups using the same color. The calculator adjusts your total automatically based on which you choose.
Should I subtract windows and doors?
Yes. A standard interior door is about 21 sq ft (3×7ft) and a typical window is also around 21 sq ft. Skipping this step leads to over-buying by half a gallon or more in larger rooms. Enter your door and window counts above and the calculator handles the deduction automatically.
Does ceiling paint count separately?
Yes, ceilings are a separate surface with a different coverage rate (flat/matte finishes spread further on smooth ceilings). Enable "Include ceiling" in the calculator to add a ceiling estimate on top of your wall total. Most bedrooms add about 0.5–1 gallon for the ceiling.
Which paint finish should I choose?
Finish affects both coverage and durability. Matte and flat finishes hide imperfections and cover about 375 sq ft per gallon, making them good for low-traffic bedroom walls. Eggshell and satin (~350 sq ft/gallon) are easier to clean, making them a better choice for hallways and kids' rooms. Semi-gloss (~325 sq ft/gallon) is best for trim, doors, and bathrooms where moisture resistance matters.
Continue with ideas and playbooks
Once your paint quantities are set, explore room ideas and step-by-step playbooks to execute the full design.