Paint Calculator: Square Feet, Coats & Gallons
Calculate how much paint you need based on surface area, number of coats and paint coverage.
Enter room dimensions or a known paintable square footage to estimate the number of gallons of paint required for the job.
Adjust for doors, windows and other openings, choose the number of coats, and enter the actual coverage of the paint you’re using. Add the price per gallon to estimate material cost.
Actual paint coverage varies by product, surface texture, application method, color change and substrate. Use the manufacturer’s stated coverage whenever possible.
Free Paint Calculator
Paint Calculator
Enter your wall dimensions or known paintable area to estimate the gallons of paint needed.
Actual paint coverage varies by paint product, substrate, surface texture, porosity, application method and color change. This calculator estimates primary paint quantity and does not separately calculate primer, trim paint, ceiling paint or specialty coatings.
How Much Paint Do I Need?
To estimate paint quantity, start by calculating the square footage of the surfaces being painted.
For all four walls of a rectangular room:
2 × (Room Length + Room Width) × Wall Height = Wall Area
For example, a 20-foot × 15-foot room with 8-foot walls has:
2 × (20 + 15) × 8 = 560 square feet of wall area
You can subtract the square footage of doors, windows and other openings that will not be painted. If you already have a takeoff, select Enter Paintable Square Feet and enter the area directly.
How Do Multiple Coats Affect Paint Quantity?
Each coat covers the same surface again, so the paintable square footage must be multiplied by the number of coats.
For example, 500 square feet receiving two coats requires:
500 × 2 = 1,000 square feet of total paint coverage
The calculator does this automatically before determining the number of gallons required.
How Many Square Feet Does a Gallon of Paint Cover?
Paint coverage varies by product and application. The calculator starts at 350 square feet per gallon as a general planning value, but the coverage field is fully adjustable.
For a job estimate, use the coverage listed by the manufacturer for the actual paint being applied whenever possible.
Real-world coverage can be affected by:
- Surface texture
- Porosity
- New or previously painted surfaces
- Application method
- Paint formulation
- Color changes
- Surface preparation
Should I Subtract Doors and Windows?
For a more detailed takeoff, you can subtract doors, windows and other areas that will not receive the paint being calculated.
Measure the opening area and enter the combined square footage in the Doors / Windows / Openings field.
For smaller jobs, some contractors may choose not to deduct every opening because the additional material can help account for normal application loss and touch-up work. The calculator leaves that decision to the estimator.
Paint Calculator Formula
The calculator uses these basic formulas:
Wall Area:
2 × (Length + Width) × Wall Height
Paintable Area:
Gross Surface Area − Openings
Total Coverage Required:
Paintable Area × Number of Coats
Gallons Required:
Total Coverage Required ÷ Coverage per Gallon
The recommended order quantity rounds up to the next full gallon.
Paint Calculator Example
Suppose you're painting a room measuring:
20 feet long × 15 feet wide × 8 feet high
The four walls contain:
2 × (20 + 15) × 8 = 560 square feet
If you are applying two coats:
560 × 2 = 1,120 square feet of coverage
At 350 square feet of coverage per gallon:
1,120 ÷ 350 = 3.2 gallons
Rounding up to full gallons gives an estimated order quantity of:
4 gallons
Use Paint Cost to Build Your Estimate
Paint is only one part of a painting estimate. Contractors may also need to account for labor, primer, masking materials, caulk, patching materials, equipment, surface preparation, cleanup, travel and overhead.
Once you know the expected paint cost, use the Contractor Job Cost Calculator to build the rest of the job cost. Then use the Contractor Markup Calculator or Contractor Profit & Margin Calculator to check your selling price and expected profitability.
Frequently Asked Questions
How do I calculate how much paint I need?
Calculate the paintable surface area, subtract any openings you do not plan to paint, multiply by the number of coats, and divide the result by the paint's square-foot coverage per gallon.
How many square feet does a gallon of paint cover?
Coverage varies by product and surface. The calculator uses 350 square feet per gallon as an adjustable planning default. For estimating a real project, use the coverage information provided for the specific paint being applied.
Does the calculator account for two coats of paint?
Yes. Enter the number of coats and the calculator multiplies the paintable area by that number before calculating the required gallons.
Should I subtract windows and doors?
You can. Enter the combined square footage of doors, windows or other openings that will not be painted. Leaving the deduction at zero calculates paint for the entire measured surface.
Can I use this calculator for exterior painting?
Yes. If you know the paintable exterior square footage, select Enter Paintable Square Feet. Adjust the coverage per gallon for the paint and surface being coated.
Does this calculator include primer?
No. Primer and finish paint may have different coverage rates and requirements. Calculate primer separately when the project requires it.