How much does a gallon of paint cover?

Manufacturers state 350 to 400 sq ft per gallon under ideal conditions. Real-world coverage on smooth surfaces with two coats typically runs 300 to 375 sq ft per gallon. Textured walls, unprimed surfaces, or dramatic color changes reduce coverage to 250 to 300 sq ft per gallon. Use the conservative end of the range when estimating.

Do I need a primer before painting?

Yes for new drywall (bare or skim-coated), any raw wood surface, dramatic color changes, or painting over oil-based paint with latex. Primer seals the surface, improves adhesion, and reduces the number of finish coats needed. Skipping primer on new drywall typically requires an extra coat of finish paint, costing more than the primer would have.

Should I buy extra paint for touch-ups?

Always buy at least one extra quart from the same production lot. Touch-up paint needs to match exactly, and a different lot can be noticeably different under certain lighting. Store the leftover with the color name, lot number, and sheen level written on the lid. This is especially important for wall colors you plan to live with for years.

How long does interior paint last before touch-up is needed?

High-quality eggshell or satin latex paint in normal use areas lasts 5 to 8 years before repainting. High-traffic areas (hallways, kids' rooms) may need a refresh at 3 to 4 years. Kitchens and bathrooms benefit from semi-gloss paint that can be wiped clean. Flat paint shows wear faster but is preferred for ceilings where sheen highlights imperfections.

Construction & EngineeringPopular

Paint Coverage Calculator

Determine how many gallons of paint you need for walls based on room dimensions, doors, windows, coats, and coverage rate.

Room Dimensions

Length (ft)

Width (ft)

Wall Height (ft)

Number of Doors

Number of Windows

Number of Coats

Coverage (sq ft/gal)

Price Per Gallon ($)

Paint Estimate

Enter room dimensions and click calculate.

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Introduction

Painters who estimate gallons by dividing total wall area by the manufacturer's stated coverage rate consistently run short. The stated coverage on a paint can label assumes ideal conditions: flat, smooth, primed surfaces and a single thin coat. In practice, a textured wall, a dramatic color change, or an unprimed surface cuts coverage by 20 to 35 percent. A painter using 400 sq ft per gallon coverage on a rough knockdown texture finish will get 280 to 310 square feet per gallon at most. On a 1,400 sq ft job, that difference means buying 2 extra gallons on the first store trip versus a second trip mid-job. According to the Painting and Decorating Contractors of America (PDCA), material estimation errors are among the top causes of preventable cost overruns on residential painting projects. This paint coverage calculator computes paintable wall area, deducts doors and windows, applies realistic coverage rates, and outputs exact gallons for each coat.

What This Calculator Does

This calculator determines how many gallons of paint are needed for a room or multi-room project. Enter room length, width, and wall height. Specify the number of standard doors (21 sq ft) and windows (15 sq ft) to deduct. Select coverage rate based on surface condition, and set the number of coats. The output includes paintable area, gallons per coat, total gallons, and material cost at your specified price per gallon. A separate ceiling calculation is included for rooms where ceilings are also being painted.

The Formula

Paintable Area = (2 x (L + W) x H) - (Doors x 21) - (Windows x 15) | Gallons = (Paintable Area x Coats) / Coverage Rate

Wall area equals the room perimeter (twice the sum of length and width) multiplied by ceiling height. Standard doors are deducted at 21 sq ft each (3 ft wide x 7 ft tall) and standard windows at 15 sq ft each (3 ft x 5 ft). The paintable net area is multiplied by the number of coats and divided by the coverage rate in sq ft per gallon. Ceiling area (optional) equals length times width and uses a separate calculation since ceiling paint differs from wall paint.

Step-by-Step Example

Measure room dimensions

Room: 15 ft x 12 ft with 9 ft ceilings. Wall area: 2 x (15+12) x 9 = 486 sq ft.

Deduct openings

Two standard doors: 2 x 21 = 42 sq ft. Two windows: 2 x 15 = 30 sq ft. Total deductions: 72 sq ft. Paintable area: 486 - 72 = 414 sq ft.

Apply coverage rate and coat count

Surface: smooth primed drywall. Coverage: 350 sq ft per gallon. Two coats. Total gallons: (414 x 2) / 350 = 2.37 gallons. Round up to 3 gallons (buying one extra quart for touch-ups). At $45/gallon: $135 in paint material.

Add ceiling if applicable

Ceiling: 15 x 12 = 180 sq ft. Ceiling paint coverage: 400 sq ft per gallon. One coat. Gallons: 180 / 400 = 0.45 gallons. Buy 1 quart. At $38/gallon: $9.50 for the quart.

Real-World Use Cases

Whole-House Interior Repaint

A painting contractor estimating a 4-bedroom, 2-bath home processes each room individually: 3 bedrooms at 250 to 300 sq ft paintable area each, living room at 580 sq ft, kitchen at 320 sq ft, and 2 baths at 180 sq ft each. Total paintable area: 2,180 sq ft walls + 1,850 sq ft ceilings. Two coats on walls at 350 sq ft/gal: 12.5 gallons. One ceiling coat at 400 sq ft/gal: 4.6 gallons. Total: 17 gallons at $42/gal = $714 in paint.

Color Change with Dark Base

A homeowner covering dark red walls with light gray. Coverage drops to 275 sq ft per gallon due to the color change requiring extra material for opacity. Room: 520 sq ft paintable. Three coats needed: (520 x 3) / 275 = 5.7 gallons. Buy 6 gallons versus 3 gallons for a same-color touch-up on the same room. The extra coats add $180 in material cost.

Rental Property Turnover

A property manager estimating paint for a 750 sq ft apartment turnover (living room 320 sq ft paintable, bedroom 210 sq ft, kitchen 140 sq ft, bath 80 sq ft). Total: 750 sq ft paintable walls. Two coats at 350 sq ft/gal: 4.3 gallons. Plus ceiling 750 sq ft / 400 sq ft/gal: 1.9 gallons. Order 5 gallons wall paint + 2 quarts ceiling. Cost at $38/gal: $190 plus labor.

Comparison

Surface Condition	Coverage Rate (sq ft/gal)	Notes
Smooth drywall, primed	350-400	Best-case scenario, new construction
Smooth drywall, unprimed	280-320	Drywall absorbs first coat
Light color over same color	350-400	One coat may suffice
Light over dark, dramatic change	250-300	Expect 3 coats minimum
Textured surface (knockdown, orange peel)	280-330	Texture increases surface area
Bare wood or plaster	200-280	Highly porous, primer essential

Common Mistakes to Avoid

Using the manufacturer maximum coverage rate. Can labels state 400 sq ft per gallon under ideal conditions. Real-world application on textured or older walls typically yields 280 to 330 sq ft. Budget at 350 sq ft/gal for smooth surfaces and 300 sq ft/gal for textured.
Assuming one coat is sufficient for a color change. Going from any medium or dark color to white or a dramatically lighter color almost always requires three coats, not two. Underestimating coat count is the leading cause of running short mid-job.
Not deducting doors and windows. A room with 2 doors and 3 windows has 87 sq ft of unpainted surface. Skipping the deduction adds nearly 0.5 gallon of paint to the estimate unnecessarily.
Buying paint in different production lots for the same room. Production lot numbers are printed on the can label. If you buy 3 gallons at the start and need a 4th gallon from a different batch, the slight color variation often appears as a streak or line at the join point.

Frequently Asked Questions

Accuracy and Disclaimer

Paint coverage estimates vary based on surface texture, porosity, application method (roller, sprayer, brush), paint quality, color change severity, and environmental conditions. This calculator uses standard assumptions. Consult your paint supplier for specific product coverage rates, especially for specialty coatings, primers, and exterior applications.

Conclusion

After confirming your gallon count, always buy one extra quart from the same production lot for touch-ups. Paint colors can vary slightly between batches, making future touch-ups with a different lot visually mismatched. For large projects with multiple rooms, run each room separately and track lot numbers per room. Combine paint cost with labor in the Material Cost Estimator. If you are also painting exterior surfaces, the paint quantity for siding, trim, and doors should be estimated separately since exterior paint has different coverage rates than interior.

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