Typical coverage rates by product type
Coverage rates below are industry-typical, single-coat ranges for orientation only — the figure on your product's technical data sheet always takes precedence.
| Product | Typical coverage (ft²/gal) | Notes |
|---|---|---|
| Interior wall paint (smooth surface) | 350–400 | Common data-sheet rating for one coat on sealed drywall |
| Primer on bare drywall | 200–300 | Porous surfaces absorb more |
| Deck stain (smooth wood) | 150–300 | Rough or weathered wood covers substantially less |
| Concrete sealer | 100–300 | Strongly dependent on porosity and sealer type |
- Coverage rates are manufacturer-published values measured under standard conditions; actual usage depends on surface porosity, texture, application method (brush, roller or sprayer) and applicator technique. Spraying typically uses more material than rolling.
- First coats on porous or unprimed surfaces cover less area per gallon than subsequent coats; some manufacturers publish separate first-coat and recoat figures.
What does a gallons per square foot calculator do?
A gallons per square foot calculator converts an area and a product coverage rate into the volume of coating to buy. Coating manufacturers publish coverage as square feet per gallon on the technical data sheet — a figure that depends on the product, the surface porosity and the application method. Interior wall paints are commonly rated in the region of 350–400 ft²/gal per coat on smooth, previously painted surfaces, while porous surfaces such as bare masonry, rough-sawn wood or unsealed concrete absorb more and cover less area per gallon.
The calculator divides the total area (multiplied by the number of coats) by the coverage rate. It also reports the reciprocal — gallons per square foot — which is useful for comparing products or budgeting large jobs where coverage is quoted per unit area.
How to use this calculator
- Enter the area to be coated in square feet (for walls: perimeter × height, minus large openings).
- Enter the coverage rate from the product's technical data sheet in square feet per gallon — 350 ft²/gal is a common figure for interior paint on smooth surfaces.
- Enter the number of coats the manufacturer specifies (two coats is typical for a color change).
- Read the gallons and liters needed, and round up to the container sizes actually sold.
The formula behind coating quantity
Gallons needed equal the area multiplied by the number of coats, divided by the coverage rate in square feet per gallon. Liters use the exact conversion 1 US gallon = 3.785411784 L, and the gallons-per-square-foot figure is simply total gallons divided by the area.
Worked example: coating 500 ft² with a product rated at 350 ft²/gal in a single coat requires 500 ÷ 350 = 1.43 gallons (about 5.41 L) — in practice, two 1-gallon cans, or one 1-gallon can plus two quarts.
Common mistakes
- Forgetting to multiply by the number of coats — a two-coat job needs twice the single-coat quantity.
- Using the smooth-surface coverage rate on rough, porous or unprimed surfaces, which can absorb far more product per square foot.
- Not rounding up to real container sizes — coatings are sold in quarts, gallons and 5-gallon pails, so 1.43 gal means buying 2 gallons (and a little extra allows touch-ups from the same batch).
- Mixing units — this calculator works in US gallons; imperial gallons (UK) are about 20% larger, and European products quote coverage in m² per liter.
الأسئلة الشائعة
How many square feet does a gallon of paint cover?
Interior wall paints are commonly rated in the region of 350–400 square feet per gallon for one coat on a smooth, sealed surface. Porous or textured surfaces cover less. The coverage figure on the specific product's technical data sheet is the number to use.
How many gallons do I need for 500 square feet?
At a typical coverage of 350 ft²/gal, 500 square feet needs 500 ÷ 350 = 1.43 gallons per coat — practically, two 1-gallon cans for one coat, or about 2.9 gallons for two coats.
Do I need more paint for the first coat?
Usually yes on new or porous surfaces. Bare drywall, masonry and weathered wood absorb more coating, so first-coat coverage is lower than the recoat figure; priming first brings coverage back toward the rated value.
Does spraying use more paint than rolling?
Airless spraying typically uses more material than brushing or rolling because of overspray and the heavier film it tends to apply; coating and equipment manufacturers commonly cite extra allowances of roughly 20–40% for spray application. Check the product data sheet for spray-specific coverage.
How do I convert square feet per gallon to square meters per liter?
Multiply the ft²/gal figure by 0.02454. For example, 350 ft²/gal ≈ 8.6 m²/L, which is how European coating manufacturers typically express coverage.
المراجع
- Coating manufacturer technical data sheets (e.g., Sherwin-Williams, Benjamin Moore, PPG) — published spreading rates in ft²/gal per coat, by product and surface type.
- Painting Contractors Association (PCA) — industry estimating guidance on coverage, coats and surface-porosity allowances.
- NIST Special Publication 811 — exact US gallon–liter conversion (1 gal = 3.785411784 L).