Free Calculators Hub
Paint Calculator
Subtracts openings from wall plus ceiling area, multiplies by coats, then divides by coverage (sq ft per gallon). Educational coverage estimate only.
Limitation: Educational coverage estimate only.
How to Estimate Paint
Sum the surfaces you will paint, subtract openings once, then apply coats and label coverage.
Enter total wall area in square feet.
Measure walls as rectangles
For each wall, length × height. Add rooms separately if colors differ so you can round purchases per color.
What Gallons Needed Means
The primary result is gallons after coats. Openings are removed before coats so you do not paint air twice.
Worked Paint Examples
Room with walls and ceiling
Inputs
Gallons needed
Net 480 sq ft × 2 coats = 960 ÷ 350 ≈ 2.75 gal.
Walls only, one coat
Inputs
Gallons needed
Net 380 ÷ 350 ≈ 1.09 gal for a single coat.
Dark-to-light needs more
Dramatic color changes often need an extra coat or a tinted primer—raise coats or lower coverage if the label warns about that.
Frequently Asked Questions
Still have questions about this calculation?
Try the CalculatorPaint Coverage Formulas
Coverage is a manufacturer claim for one coat on a prepared surface—not a guarantee for every wall.
Formula
Net area
walls + ceiling − openings
Paintable area
net area × coats
Gallons
paintable ÷ coverage (sq ft/gal)
Scientific Background
Assumptions: uniform coverage, flat surfaces, user-supplied openings. Limitations: no porous drywall vs previously painted differences beyond the coverage number you enter.
Sources & review
Paint Calculator documents the references behind its formulas and assumptions. Always treat results as educational estimates, not personalized professional advice.
Last reviewed
July 22, 2026
Free Calculator Hub methodology
Free Calculator Hub
/methodology
See our methodology and corrections policy.