Gallons per Square Foot Calculator
Turn a coverage rate into the gallons you actually need. Enter the area (or length × width), a rate in gallons per sq ft or sq ft per gallon — or pick a product preset — add coats and a little waste, and get total gallons, containers to buy, the effective gal/sq ft, and estimated cost, with comparison tables and a downloadable PDF.
| Product | Sq ft/gal | Gal/sq ft | Gallons | Cost |
|---|---|---|---|---|
| Enter an area to compare products | ||||
| Coats | Total gallons | Buy | Cost |
|---|---|---|---|
| Enter an area to compare coats | |||
Gallons per Square Foot Calculator — Complete Guide for 2026
Paint, stain, sealer, epoxy, roof coating, and even irrigation water are all bought by the gallon but applied over an area measured in square feet. The link between the two is the coverage rate — how many square feet one gallon covers, or how many gallons each square foot takes. Get it right and you buy exactly enough to finish; get it wrong and you are either making a second trip to the store or storing half-empty cans.
Our free Gallons per Square Foot Calculator takes your area (or length × width), a coverage rate in either square feet per gallon or gallons per square foot — or a product preset — plus coats and a waste allowance, and returns total gallons, the containers to buy, the effective gallons per square foot, and an estimated cost. Comparison tables by product and by number of coats, a gallons-by-product chart, and a downloadable PDF round it out.
How to Use the Gallons per Square Foot Calculator in 4 Steps
A complete estimate takes under a minute. Enter the area and coats, set the coverage rate from the label or a preset, add waste and container size, and download a PDF to take to the store or share with a crew.
Enter the Area & Coats
Type the area in square feet, or tap Length × Width and enter both dimensions in feet. Then choose 1 to 4 coats or passes — sealers are often one coat, while paints and stains commonly need two. Each coat multiplies the gallons needed. Results update live.
Set the Coverage Rate
Pick a product preset — exterior paint, deck stain, concrete sealer, epoxy floor, driveway sealer, roof coating, or lawn watering — or choose Custom and type the rate from the label. Toggle between sq ft / gallon (label style, like 250) and gallons / sq ft (like 0.004); switching converts the value automatically. The rate is per coat.
Add Waste, Container & Price
Enter a waste / overage percentage for spills, uneven absorption, and touch-ups — 10% is the default. Choose how the product is sold: quart, 1-gallon can, 5-gallon pail, or 55-gallon drum. Add your price per gallon; the cost uses the rounded-up amount you actually buy.
Review & Download the Report
The hero result shows total gallons needed. Cards add the area, the effective gallons per square foot (including coats and waste), and the estimated cost. The breakdown shows base gallons, waste added, containers, and the rounded buy amount. Compare products and coats in the tables and chart, then click Download report.
Coverage Rates, Reciprocals, and Why Thickness Matters
A coverage rate can be written two ways. Square feet per gallon — the format on most paint, stain, and sealer labels — tells you how far one gallon goes. Gallons per square foot tells you how much each square foot takes. They are reciprocals: divide 1 by either one to get the other. 350 sq ft/gal is 0.0029 gal/sq ft; 80 sq ft/gal is 0.0125 gal/sq ft. Gallons per square foot is convenient because you can multiply it straight by an area.
Behind every rate is a film thickness. A US gallon is exactly 231 cubic inches. Spread 1 mil (0.001 in) thick, it covers 231,000 square inches — about 1,604 square feet. So a product rated at 250 sq ft/gal goes on about 1,604 ÷ 250 ≈ 6.4 mils wet, while a roof coating at 50 sq ft/gal goes on about 32 mils. Thicker, heavier products cover less area per gallon, and that is why coverage varies so widely between product types.
The same math works for water
Water depth converts the same way. One square foot covered 1 inch deep holds 144 cubic inches, and 144 ÷ 231 ≈ 0.623 gallons. That is the calculator’s Lawn watering preset: 1 inch of water over 1,000 sq ft of lawn is about 623 gallons, and over an acre it is about 27,154 gallons — the figure irrigation planners call an acre-inch.
What the Gallons per Square Foot Calculator Calculates
Every output comes from the same area, coats, coverage rate, and waste allowance, so gallons, containers, effective rate, and cost always agree with each other and with the tables and chart.
Total Gallons Needed (Hero Result)
Base gallons (area × coats × gal/sq ft) plus the waste allowance. The breakdown lists base gallons and waste added separately so you can see both. At the default inputs — 500 sq ft, one coat, 250 sq ft/gal, 10% waste — the result is 2.2 gallons.
Containers & Buy Amount
Total gallons ÷ container size, always rounded up — quarts (0.25 gal), 1-gallon cans, 5-gallon pails, or 55-gallon drums. The buy amount is the whole containers you actually purchase. At the defaults, 2.2 gallons means 3 × 1-gallon cans, or 3 gallons to buy.
Effective Gallons per Square Foot
Total gallons ÷ area, including coats and waste — the true rate for your job, not just the label rate. At the defaults it is 0.0044 gal/sq ft versus the label’s 0.0040. The breakdown also shows your rate both ways: sq ft/gal and gal/sq ft.
Estimated Cost
Buy amount × price per gallon. Because stores sell whole containers, cost is based on the rounded-up amount, not the exact gallons — which is why it can jump when you cross a container boundary. At the defaults, 3 gallons at $35 per gallon is $105.
Coverage-Rate & Coats Tables + Chart
The by-coverage-rate table compares your rate with six common products — exterior paint, deck stain, concrete sealer, epoxy, driveway sealer, roof coating — for your area and coats. The by-coats table shows gallons, buy amount, and cost for 1 to 4 coats, and the bar chart plots gallons needed by product.
PDF Report
The PDF includes a branded header, the total gallons, an inputs-and-results table, the coverage-rate comparison table, the coats table, and a note reminding you to check the product label — ready to take to the store, attach to a quote, or share with a painting or sealing crew.
Gallons per Square Foot Chart — Common Coverage Rates
Gallons shown are for one coat, before waste. Highlighted rows match the calculator’s product presets. Actual coverage varies by product and surface — always check the label.
| Sq Ft per Gallon | Gal per Sq Ft | Gal per 100 Sq Ft | Gal per 1,000 Sq Ft | Typical Use |
|---|---|---|---|---|
| 400 sq ft/gal | 0.0025 | 0.25 gal | 2.50 gal | Smooth, sealed surfaces — high end of many paint labels |
| 350 sq ft/gal | 0.0029 | 0.29 gal | 2.86 gal | Exterior paint preset |
| 300 sq ft/gal | 0.0033 | 0.33 gal | 3.33 gal | Paint on lightly textured surfaces |
| 250 sq ft/gal | 0.0040 | 0.40 gal | 4.00 gal | Deck stain preset; calculator default |
| 200 sq ft/gal | 0.0050 | 0.50 gal | 5.00 gal | Concrete / masonry sealer preset |
| 150 sq ft/gal | 0.0067 | 0.67 gal | 6.67 gal | Epoxy garage floor preset |
| 100 sq ft/gal | 0.0100 | 1.00 gal | 10.00 gal | Heavy-bodied coatings; rough or porous surfaces |
| 80 sq ft/gal | 0.0125 | 1.25 gal | 12.50 gal | Asphalt driveway sealer preset |
| 50 sq ft/gal | 0.0200 | 2.00 gal | 20.00 gal | Elastomeric roof coating preset |
| 25 sq ft/gal | 0.0400 | 4.00 gal | 40.00 gal | Very thick coatings and fillers |
| 1.6 sq ft/gal | 0.6234 | 62.34 gal | 623.38 gal | Lawn watering preset — 1 inch of water |
Multiply by the number of coats and add your waste allowance (commonly 5–10%) before buying. Rough, porous, or bare surfaces often need noticeably more than the label rate.
Gallons per Square Foot — Rate Conversions and Water Depth
The table on the left converts a label’s coverage rate into the other forms you may run into — gallons per square foot, metric coverage in square meters per liter, and the approximate wet film thickness it implies. The table on the right shows how much water it takes to cover an area to a given depth, which is what the Lawn watering preset is based on.
| Sq ft/gal | m² per liter | Wet film |
|---|---|---|
| 400 | 9.8 m²/L | ≈ 4.0 mils |
| 350 | 8.6 m²/L | ≈ 4.6 mils |
| 300 | 7.4 m²/L | ≈ 5.3 mils |
| 250 | 6.1 m²/L | ≈ 6.4 mils |
| 200 | 4.9 m²/L | ≈ 8.0 mils |
| 150 | 3.7 m²/L | ≈ 10.7 mils |
| 100 | 2.5 m²/L | ≈ 16.0 mils |
| 80 | 2.0 m²/L | ≈ 20.1 mils |
| 50 | 1.2 m²/L | ≈ 32.1 mils |
| Water depth | Per sq ft | Per 1,000 sq ft |
|---|---|---|
| 0.25 in | 0.156 gal | 156 gal |
| 0.5 in | 0.312 gal | 312 gal |
| 0.75 in | 0.468 gal | 468 gal |
| 1 in | 0.623 gal | 623 gal |
| 1.5 in | 0.935 gal | 935 gal |
| 2 in | 1.247 gal | 1,247 gal |
| 1 in over 1 acre | 43,560 sq ft | 27,154 gal total |
Gallons per Square Foot — Key Numbers
The Gallons per Square Foot Calculator Is Built For You If…
Whether you’re staining a deck, sealing a driveway, coating a roof, or planning how much to water a lawn, this calculator turns square footage and a label rate into the gallons, containers, and cost you need in seconds.
Homeowners & DIY Painters
Paint, stain, sealers & epoxyYou know the square footage of the deck or garage floor, and the can says it covers “250 sq ft per gallon.” A homeowner staining a 500 sq ft deck with two coats needs 4.4 gallons with waste — so one 5-gallon pail may beat five single cans. Someone coating a two-car garage with epoxy can check whether one kit is enough before starting.
- Enter length × width for decks, floors, and driveways
- Set coats to 2 for most paints and stains
- Compare 1-gallon cans and 5-gallon pails for cost
- Bring the PDF to the paint counter
Painting, Sealing & Roofing Contractors
Quotes, material orders & job sheetsMaterial cost is a big part of every coating quote, and running out mid-job costs a return trip. A sealcoating crew can price a driveway at 80 sq ft per gallon; a roofer can size elastomeric coating at 50 sq ft per gallon in drums or pails. The coats table makes it easy to show a client what a second coat adds to the budget.
- Use the manufacturer’s spec rate, not a generic preset, for quotes
- Show 1-coat vs 2-coat cost from the coats table
- Switch container size to 5-gallon pails or 55-gallon drums for big jobs
- Attach the PDF to estimates and supplier orders
Gardeners, Landscapers & Property Managers
Watering, treatments & maintenanceLawns are often watered by the inch, and liquid treatments are applied at a set rate per area. The Lawn watering preset shows that 1 inch over 1,000 sq ft is about 623 gallons. Property managers budgeting recurring sealer or coating maintenance across many surfaces can compare products side by side.
- Use the Lawn watering preset (0.623 gal/sq ft per inch of water)
- Set coats to the number of inches or passes you plan to apply
- Switch to gal/sq ft mode for treatments labeled per square foot
- Keep PDFs for recurring maintenance budgets
7 Tips for Accurate Gallon Estimates
The math is simple; the coverage rate is where estimates go wrong. These tips help you pick a realistic rate and buy the right amount the first time.
Use the Rate From Your Product’s Label
Presets are typical values, but coverage varies a lot between brands and product lines. When the label gives a range, such as 250–400 sq ft per gallon, use the lower number for a conservative estimate, especially on rough or porous surfaces.
Label Rates Are for One Coat
Coverage on the can is per coat. Two coats need twice as much product, three coats three times as much. Set the coats field instead of adjusting the rate, so the tables and PDF show the job correctly.
Expect Rough and Porous Surfaces to Drink More
Bare wood, weathered decks, new concrete, stucco, and split-face block absorb far more than smooth, sealed surfaces. The first coat on a porous surface often covers much less than the label rate. Raise the waste percentage, lower the rate, or plan for an extra coat.
Measure Only What You’ll Coat
For walls, subtract large openings like garage doors and big windows. For decks, include railings and steps, which add surprising area. For floors and driveways, length × width is usually enough; split odd shapes into rectangles and add them.
Compare Container Sizes Before Buying
The calculator rounds up to whole containers, so the buy amount jumps at each container boundary. When you need four or more gallons, a 5-gallon pail is often cheaper per gallon than single cans. Switch the container size to see the difference, then enter each size’s real price.
Keep Some Leftover for Touch-Ups
A small waste allowance (5–10%) covers spills and roller loss, and a little leftover from the same batch is valuable for future touch-ups. Label and store it. Mixing batches later can cause visible color or sheen differences.
Know Which Mode You’re Using
“250” means something very different as sq ft per gallon than as gallons per sq ft. If a spec gives gallons per square foot or per 100 sq ft, switch to Gallons / sq ft mode (divide per-100 figures by 100 first). The calculator converts the value when you switch modes so the physical rate stays the same.
Gallons per Square Foot Calculator — Frequently Asked Questions
Everything you need to know about converting coverage rates, figuring the gallons for a job, accounting for coats and waste, and watering by the inch.
Gallons per square foot is 1 divided by the coverage rate in square feet per gallon. For example, a product that covers 250 sq ft per gallon uses 1 ÷ 250 = 0.004 gallons per square foot.
To find the gallons for a job, multiply the area by the gallons per square foot and by the number of coats: gallons = area × coats × gal/sq ft, which is the same as area × coats ÷ sq ft per gallon.
It depends on the coverage rate and number of coats. At 250 sq ft per gallon, one coat on 500 sq ft needs 500 ÷ 250 = 2 gallons, or 2.2 gallons with 10 percent waste, so you would buy three 1-gallon cans.
At 350 sq ft per gallon it is about 1.6 gallons with waste, and at 80 sq ft per gallon, typical of asphalt driveway sealer, it is about 6.9 gallons.
They are two ways of stating the same coverage rate, and each is the reciprocal of the other. Product labels usually give square feet per gallon, such as 250 sq ft/gal. Gallons per square foot is the same rate flipped, 1 ÷ 250 = 0.004 gal/sq ft, and is handy for multiplying directly by an area.
The calculator accepts either and converts between them.
Coverage rates on labels are for one coat, so each additional coat adds the same amount again. Two coats need twice the product of one coat, and three coats need three times as much.
For 500 sq ft at 250 sq ft per gallon with 10 percent waste, one coat is 2.2 gallons, two coats 4.4 gallons, and three coats 6.6 gallons.
About 0.623 gallons. One square foot at 1 inch deep is 144 cubic inches, and a US gallon is 231 cubic inches, so 144 ÷ 231 ≈ 0.623 gallons.
That means 1 inch of water over 1,000 sq ft of lawn is about 623 gallons, and 1 inch over an acre is about 27,154 gallons. The calculator’s Lawn watering preset uses 0.623 gal/sq ft.
A 5 to 10 percent allowance is common to cover spills, uneven absorption, and touch-ups. Rough, porous, bare, or weathered surfaces absorb much more than a label’s rate, so plan for more product or an extra coat on those.
The calculator also rounds up to whole containers, so the amount you buy is usually a little more than the gallons needed.
The arithmetic is exact: gallons = area × coats × gallons per square foot × (1 + waste), with containers rounded up to whole units and cost based on the rounded amount.
The accuracy of the result depends on the coverage rate. Preset rates are typical published values, and real coverage varies with the product, surface texture and porosity, application method, and temperature, so always check the product label.
Accuracy note: The HomeExpertly Gallons per Square Foot Calculator uses gallons per square foot = 1 ÷ square feet per gallon and total gallons = area × coats × gallons per square foot × (1 + waste %), then rounds up to whole containers of the size you choose; cost is based on that rounded amount. Water depth uses 1 US gallon = 231 cubic inches, so 1 inch over 1 square foot ≈ 0.623 gallons. Preset coverage rates (exterior paint 350, deck stain 250, concrete sealer 200, epoxy 150, driveway sealer 80, and roof coating 50 sq ft per gallon) are typical published values; actual coverage varies with the product, surface texture and porosity, application method, weather, and temperature. Cost estimates depend entirely on the price you enter and exclude primers, tools, taxes, and labor. Results are for informational and planning purposes only. Always follow the manufacturer’s label and technical data for coverage, number of coats, and application conditions, and follow local watering rules and restrictions. HomeExpertly is not responsible for any consequences arising from the use of these estimates.