Gallons per Square Foot Coverage Calculator
Find how many gallons you need to cover an area, from your product’s coverage rate.
Reviewed by the ToolNestr Editorial Team — July 2026
How the coverage calculator works
Every liquid coating — paint, primer, stain, sealer — has a coverage rate printed on the label, given in square feet per gallon. That number is how far one gallon spreads while still laying down at the film thickness the manufacturer intends. To find how much you need, divide the area you are covering by that coverage rate; the result is the gallons for a single coat.
Most jobs need more than one coat, so the calculator multiplies the single-coat gallons by the number of coats. Two coats of wall paint roughly doubles the paint required. The exact answer almost never lands on a whole number, so it is rounded up to the next whole gallon, because coatings sell in whole cans and running short mid-wall leaves a visible lap line or a color mismatch from a new batch.
It also helps to separate the coverage rate for a first coat from later coats. Bare drywall, new wood, and unsealed concrete are porous and drink up more product on the first pass, while later coats glide over an already-sealed surface and go further. Manufacturers publish a single coverage figure as a practical average, but professionals often budget slightly more for the first coat and slightly less for subsequent ones when working on new or unfinished substrates.
Coverage rates follow manufacturer norms: interior wall paint spreads about 350 to 400 square feet per gallon, primer and porous surfaces far less, and heavy solid stains or textured surfaces less still. Rough, unsealed, or highly absorbent surfaces soak up more, so pick a rate at the low end of the label range when in doubt. The estimate assumes even application over a sound surface.
Coverage-rate ranges reflect typical manufacturer spread-rate labeling for architectural coatings, consistent with ASTM D5146 test methods for coating film properties.
Measure the area
Total square feet of wall, deck, or floor.
Read the label rate
Square feet per gallon for your product.
Set the coats
Get whole gallons to buy for the job.
The formula explained
Per coat
= area ÷ coverage rate. 900 sq ft at 350 sq ft/gal: 900 ÷ 350 = 2.57 gal per coat.
All coats
× coats. Two coats: 2.57 × 2 = 5.14 gal exact.
Round up
5.14 → 6 gallons to buy, leaving a little for touch-ups.
Worked example
A 500 sq ft deck getting 2 coats of solid stain at 200 sq ft/gal.
Use cases for the coverage calculator
Interior wall paint
Bedrooms, living rooms, and hallways typically get two coats. Calculating the exact gallons needed avoids buying an extra can you do not need or running short mid-wall.
Deck and fence stain
Semi-transparent and solid stains have much lower coverage rates than wall paint, especially on rough-sawn lumber, so this calculator helps avoid underestimating a deck refinishing job.
Driveway and concrete sealer
Sealers spread differently depending on whether the concrete is broom-finished or smooth. Entering the correct coverage rate for the surface texture keeps the estimate accurate.
Primer and specialty coatings
Primers, epoxy floor coatings, and waterproofing membranes often have much lower coverage rates than finish coats. This tool works for any coating as long as you know its labeled spread rate.
Real-world context
A standard bedroom repaint is the most common job this calculator handles. A 400 sq ft wall area at a typical 375 sq ft/gal coverage rate, two coats, needs (400 ÷ 375) × 2 = 2.13 gallons exact — round up to 3 gallons, since paint only sells in whole cans and 2 gallons would leave the second coat short.
Driveway sealing is usually a single-coat job with a lower coverage rate. A 600 sq ft driveway sealed at 300 sq ft/gal for one coat needs exactly 600 ÷ 300 = 2 gallons — a case where the exact math lands on a whole number, so no rounding waste at all.
Deck staining sits in between. A 350 sq ft deck getting two coats of stain at 250 sq ft/gal needs (350 ÷ 250) × 2 = 2.8 gallons exact, rounding up to 3 gallons — the extra 0.2 gallons of headroom is typically enough for touch-ups on rail spindles and stair edges that get missed on the first pass.
Common misconceptions
"The coverage rate on the can is exact for any surface." It is a best-case number. Label coverage rates assume a smooth, properly prepared surface applied at the recommended film thickness. Rough, porous, or unprimed surfaces soak up significantly more product, so real-world coverage often runs lower than the label states.
"Two coats always use exactly double the paint of one coat." Close, but not exact. The first coat on bare or porous material typically absorbs more product than the second coat, which goes over an already-sealed surface. Two coats usually uses somewhat less than double the paint of a single coat on new drywall or wood.
Related calculators
Frequently asked questions
How many gallons do I need to cover a given area?
Divide the area in square feet by the product coverage rate in square feet per gallon, then multiply by the number of coats. For 900 sq ft at 350 sq ft/gal and one coat: 900 ÷ 350 = 2.57 gallons, rounded up to 3 gallons.
What coverage rate should I use?
Use the figure on the product label. Interior wall paint typically covers 350 to 400 sq ft per gallon, primer 200 to 300, semi-transparent deck stain 200 to 300, solid stain 150 to 250, and concrete sealer 250 to 400. Rough or porous surfaces cover at the lower end.
Do I need to add for multiple coats?
Yes. Each coat needs its own share of paint, so two coats roughly double the gallons. The calculator multiplies the single-coat amount by the number of coats you enter, then rounds up to whole cans.
Why round up to whole gallons?
Paint and coatings are sold in whole gallons and quarts, and running out mid-job risks a visible lap mark or a slightly different batch color. Rounding up ensures you finish the job, with a little left for touch-ups.
Sources & references
This tool uses standard formulas and reference values from:
- • American Concrete Institute — ACI 318, Building Code Requirements for Structural Concrete. concrete.org
- • ICC — International Residential Code (IRC), span, footing and framing tables. codes.iccsafe.org
- • APA – The Engineered Wood Association, allowable span and load guidance.
Estimates for planning only. Span, load and code values vary by jurisdiction — verify against your local adopted code and a licensed engineer before building.