Paint amount + coverage + cost
Paint Calculator
Enter room dimensions or paintable square footage to estimate how many gallons to buy for interior walls, ceilings, or exterior walls. You can refine coverage, primer, and cost assumptions when you need a more detailed estimate.
Example estimate
- Net wall area
- 365 sq ft
- Area incl. coats + waste
- 803 sq ft
- Assumptions
- 2 coats · 10% waste
Example only. Your result uses the measurements and options you enter below.
Your estimate
Your paint estimate will appear here
Enter your measurements and select Calculate Paint Needed to see how much paint to buy, the paintable area, and a breakdown of the calculation.
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Formula
How the paint calculation works
The page uses deterministic formulas for paint quantity, primer, DIY cost, and professional labor ranges.
Room wall area
Gross Wall Area = 2 x (Room Length + Room Width) x Wall Height
Net paintable area
Net Paintable Area = Gross Surface Area - Doors - Windows - Garage Door Area
Paint gallons
Paint Gallons = Net Area x Coats x (1 + Waste Allowance) / Coverage
DIY cost
Total DIY Cost = Paint Cost + Primer Cost + Supplies Cost
Example: How much paint for a 12 × 14 ft room?
Assume 8 ft walls, one 21 sq ft door, two 15 sq ft windows, two coats, 10% extra for waste, and paint rated at 350 sq ft per gallon.
- Wall area: 2 × (12 + 14) × 8 = 416 sq ft.
- Paintable area: 416 − 21 − (2 × 15) = 365 sq ft.
- Area with two coats and waste: 365 × 2 × 1.10 = 803 sq ft.
- Paint to buy: 803 ÷ 350 = 2.29 gallons, rounded up to 3 gallons.
This is a planning example. Your estimate uses the measurements and coverage you enter; check the coverage listed for the paint you plan to buy.
Coverage reference
Typical paint coverage by surface
Use 2 coats for most color changes.
Porous siding may need more paint.
Recommended for new drywall, stains, or dark-to-light changes.
Flat ceiling paint often covers similarly to wall paint.
Use cases
Built for common home painting estimates.
Interior Paint Calculator
Estimate walls by room dimensions, doors, windows, coats, coverage, and waste.
Exterior Paint Calculator
Use house perimeter, wall height, stories, gables, openings, and exterior coverage.
Ceiling Paint Calculator
Calculate ceiling paint from room length, width, coat count, and ceiling paint coverage.
Paint Cost Calculator
Optionally compare paint, primer, supplies, and labor costs using rates you enter.
FAQ
Paint calculator questions
How much paint do I need for one room?
Measure the room perimeter, multiply by wall height, subtract doors and windows, then multiply by coats and divide by paint coverage. A typical 12 by 14 ft room with two coats often needs about 3 gallons.
How many square feet does one gallon of paint cover?
Most interior wall paints cover about 350 sq ft per gallon on smooth surfaces. Primer is commonly closer to 250 sq ft per gallon.
Should I include primer?
Include primer for new drywall, patched surfaces, stains, exterior painting, or dark-to-light color changes.
How do I calculate paint for a ceiling?
Ceiling area is room length times room width. Multiply by the number of coats, add waste allowance, then divide by ceiling paint coverage.
Can this work for Sherwin-Williams, Behr, Benjamin Moore, Home Depot, or Lowe's paint?
Yes. Use the coverage and price listed on the specific product label for a better estimate.
References
Sources behind this calculator
Coverage guidance informs the estimate; form design guidance explains which inputs start blank. Always use your paint product’s stated coverage when available.
Paint quantity guidance
Sherwin-Williams explains the area ÷ product coverage method and why surface texture and application can change real-world coverage.
Sherwin-Williams painting FAQs ↗Form design guidance
Project measurements start blank; editable common assumptions stay filled in. Labels remain visible outside the fields.
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