How much paint do I need?
Measure the paintable surface area, divide by product coverage per gallon, then add waste for texture, edges, touchups, and small parts. In the default example, 400 sq ft at 250 sq ft per gallon with 10% waste returns 2 gallons.
Use the product coverage label
Coverage changes by coating type, surface texture, porosity, primer need, color change, spray loss, and number of coats. Replace the default coverage with the selected product label before buying.
Estimate separate surfaces separately
If the project has metal, wood, masonry, plastic, or patched sections, calculate each surface with the coating and coverage that matches that section.
Stain and sealer coverage examples
Examples use broad planning coverage. Rough, dry, or weathered wood may need more stain or sealer.
| Surface | Measured area | Estimated gallons |
|---|---|---|
| Deck boards | 300 sq ft | 2 gallons |
| Deck rails | 220 sq ft | 2 gallons |
| Fence face | 600 sq ft | 3 gallons |
| Wood siding | 1,200 sq ft | 6 gallons |
Before you calculate
- Measure boards, rails, posts, stairs, siding, pergolas, and fence faces separately.
- Use lower coverage for rough, dry, weathered, or very porous wood.
- Check whether the product coverage is for one coat or the full recommended system.
Common mistakes
- Using deck floor area only when rails, stairs, or posts are also being stained.
- Ignoring wood porosity, sanding, previous coatings, or second coats.
- Combining transparent stain, solid stain, and sealer under one coverage number.
Formula
units = ceil((area * (1 + wastePercent / 100)) / coveragePerUnit)
Assumptions
- Coverage changes with wood species, age, porosity, roughness, previous coatings, and application method.
- Rails, pickets, posts, deck boards, stairs, and both fence sides should be measured consistently.
- Use the exact stain or sealer label for final coverage and coat assumptions.
Example
Estimated wood sealer needed (gallons): 2 gallons
How to estimate paint gallons
- Measure the paintable surface area in square feet, subtracting only major openings when appropriate.
- Enter paint coverage per gallon from the product label and include the number of coats when the project needs more than one coat.
- Add waste or touch-up allowance for texture, color changes, overspray, trim edges, and small parts.
- Divide adjusted paint area by coverage per gallon and round up to whole gallons or containers; the default example returns 2 gallons.
- Check primer, prep, masking, trim paint, and sprayer or roller needs separately from paint quantity.
Before you buy materials
- Round up to full gallons or containers and keep extra for touchups.
- Use the selected stain or sealer label as the final coverage source.
FAQ
How do I calculate paint for wood sealer?
Measure paintable surface area, divide by coverage per gallon, add waste, and round up to whole gallons or containers.
How many gallons for 400 sq ft in this example?
At 250 sq ft per gallon with 10% waste, the default estimate is 2 gallons.
Should I add waste for small parts and edges?
Yes. Small project surfaces can lose material to masking, brush loading, spray loss, texture, edges, and touchups.
Does this choose the right paint type?
No. It estimates quantity only. Choose coating type, prep method, primer, and surface compatibility separately.
Related calculators
This calculator is for planning estimates only. Verify final quantities with product labels, project conditions, and a qualified professional when accuracy matters.