Application rates for paint, sealer, epoxy, fertiliser, irrigation and rainfall are all “volume per area” figures, but labels mix gallons per square foot, square feet per gallon and litres per square metre. Converting between them tells you how many cans to buy, how thick a coating will be or how deep a given volume of water would stand on a floor or field.
How to use the Gallons per Square Foot Calculator
- Volume of liquid
- Area covered
- Every result field is editable: type into Application rate and Volume of liquid plus every other field update to match.
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the volume and the area it covers. The calculator divides one by the other and expresses the result as an application rate, a coverage rate and a layer thickness. Type a target rate into the result to find the volume you need for that area.
Common rates
| Use | Typical rate |
|---|---|
| Interior wall paint | 350–400 ft²/gal (≈ 0.1 L/m²) |
| Deck stain | 150–250 ft²/gal |
| Garage-floor epoxy | 250–300 ft²/gal per coat |
| 1 inch of rain or irrigation | 0.623 gal/ft² (25.4 L/m²) |
Tips for an accurate estimate
- Measure every dimension twice and write the unit next to each number – most estimating errors are unit mix-ups (inches entered as feet).
- Pick the unit in each field’s menu instead of converting by hand; the calculator converts everything to the same base before it multiplies.
- Round up only at the very end. Rounding each dimension first can add several percent to the final quantity.
- Suppliers sell in whole units – bags, boxes, sheets or quarter yards – so always round the final order up, not down.
Common mistakes to avoid
- Mixing square and cubic units: square feet measure area, cubic yards measure volume, and you need a depth to go from one to the other.
- Using nominal lumber sizes where actual sizes matter (a 2×4 is really 1½ × 3½ in).
- Forgetting that 1 yd³ = 27 ft³, not 9 ft³ (9 is for square yards).
Inputs explained
| Field | What to enter |
|---|---|
| Volume of liquid | Units: US gal, L, m³, ft³, UK gal |
| Area covered | Units: ft², m², yd², acre |
What each result means
- Application rate = [Volume of liquid]÷[Area covered]
- Coverage = [Area covered]÷[Volume of liquid]
- Equivalent layer depth = [Volume of liquid]÷[Area covered]
Formula
Gallons per ft² = volume (gal) ÷ area (ft²)Coverage = area ÷ volumeDepth = volume ÷ area (1 gal/ft² ≈ 1.604 in)Worked example
Inputs — Volume of liquid: 5 US gal; Area covered: 500 ft².
Results — Application rate = 0.01 gal/ft²; Coverage = 100 ft²/gal; Equivalent layer depth = 0.016 in.
Frequently asked questions
How deep is 1 gallon per square foot?
About 1.604 inches (40.7 mm), because a gallon is 231 in³ spread over 144 in².
How do I convert ft²/gal to L/m²?
Divide 40.746 by the ft²/gal figure. Paint covering 400 ft²/gal is about 0.10 L/m², or roughly 9.8 m²/L.
How thick is paint at 400 ft² per gallon?
The wet film is about 4 mils (0.1 mm); the dry film is thinner, depending on the solids content.
What formula does the Gallons per Square Foot Calculator use?
Gallons per ft² = volume (gal) ÷ area (ft²).