Paint Coverage Calculator

Find out exactly how much paint you need for your next project. Enter your room dimensions below and our calculator will estimate the total wall area, paintable surface area, and gallons required.

Understanding Paint Coverage Rates

Paint coverage is measured in square feet per gallon, and it varies depending on the type of paint, the surface being painted, and the application method. Most latex interior paints cover approximately 350 to 400 square feet per gallon on smooth, previously painted surfaces. Our calculator uses 350 square feet per gallon as a conservative, reliable estimate that accounts for real-world conditions rather than the ideal laboratory conditions listed on paint cans.

Premium paints from brands like Benjamin Moore Regal Select and Sherwin-Williams Duration tend to offer better coverage per gallon due to higher concentrations of pigment and binder. Budget paints may require additional coats to achieve the same opacity, which can offset any initial cost savings. When comparing paint prices, always consider the coverage rate alongside the per-gallon cost to get an accurate picture of your total investment.

Exterior paints generally have slightly lower coverage rates, typically 250 to 350 square feet per gallon, because exterior surfaces tend to be more textured and porous. Stucco, brick, and rough-sawn wood siding absorb more paint than smooth interior drywall. If you are painting a textured exterior surface for the first time, plan for coverage closer to 200 square feet per gallon for the first coat.

When Do You Need Primer?

Primer is a specialized undercoat that improves paint adhesion, blocks stains, and provides a uniform base color. You should use primer in the following situations:

• New drywall: Unpainted drywall is highly porous and will absorb paint unevenly without primer. A PVA (polyvinyl acetate) primer seals the surface and creates a consistent base for your topcoat.
• Dramatic color changes: Going from a very dark color to a light one (or vice versa) requires a tinted primer to prevent the old color from showing through. Without primer, you may need four or more coats of paint to achieve full coverage.
• Stain coverage: Water stains, smoke damage, crayon marks, and ink marks require a stain-blocking primer such as shellac-based Zinsser B-I-N or Kilz Original. Regular paint alone will not prevent these stains from bleeding through.
• Glossy surfaces: Semi-gloss or high-gloss surfaces need to be lightly sanded and primed before repainting to ensure the new coat adheres properly. A bonding primer like Stix by Insl-X works well on slick surfaces.
• Bare wood: Raw wood requires a wood primer to seal the grain, prevent tannin bleed, and provide a stable base for paint. Oil-based primers work particularly well on knotty woods like pine and cedar.

Modern paint-and-primer-in-one products are suitable for repainting walls that are already in good condition with a similar color. However, they are not a substitute for dedicated primer in the situations listed above. Professional painters almost always use a separate primer coat because it consistently produces better results and longer-lasting finishes.

How Room Shape Affects Paint Calculations

Our calculator assumes a standard rectangular room, which works well for most bedrooms, living rooms, and offices. However, many homes have rooms with irregular shapes, alcoves, bump-outs, vaulted ceilings, or partial walls that affect the total area.

For L-shaped rooms, measure each rectangular section separately and add the wall areas together. For rooms with vaulted or cathedral ceilings, measure the tallest wall height and shortest wall height, then calculate the average. Triangular gable walls can be calculated as half the base width multiplied by the height of the peak.

Rooms with extensive built-in shelving, wainscoting, or chair rail molding may require less wall paint but additional trim paint. A standard interior door opening is approximately 21 square feet (3 feet wide by 7 feet tall), and a standard window is approximately 15 square feet (3 feet wide by 5 feet tall). Our calculator subtracts these standard sizes from the total wall area to give you a more accurate paint estimate.

For hallways and stairwells, measure each wall individually since opposite walls often have different dimensions. Stairwells can be particularly tricky because the walls follow the angle of the stairs, creating triangular and trapezoidal shapes. When in doubt, round up your measurements to ensure you purchase enough paint.

Tips for Buying the Right Amount of Paint

Running out of paint mid-project is one of the most common frustrations homeowners face. Here are practical tips for ensuring you buy the right amount:

Always round up. If your calculation says you need 2.3 gallons, buy 3 gallons. Paint is sold in quarts and gallons, so you will rarely purchase the exact amount you need. Having leftover paint is valuable for future touch-ups.

Keep extra paint for touch-ups. Store at least a quart of each color used in your home. Small scuffs, nail holes, and marks are inevitable, and having matching paint on hand makes repairs seamless. Label each container with the room, brand, color name, color code, and finish.

Consider the paint finish. Different sheens have slightly different coverage rates. Flat and matte paints tend to cover slightly more area per gallon than semi-gloss or high-gloss paints because of their thicker consistency. Flat finishes also hide surface imperfections better, which is why they are the most popular choice for ceilings and low-traffic areas.

Factor in surface texture. Textured walls, popcorn ceilings, and rough plaster absorb significantly more paint than smooth surfaces. If your walls have a heavy texture such as knockdown, orange peel, or skip trowel, increase your paint estimate by 15 to 25 percent over the standard coverage rate.

Buy all your paint at once. Paint colors can vary slightly between batches, even with the same formula. Purchasing all your paint at once from the same store ensures color consistency across your entire project. If you need multiple gallons, ask the store to box (intermix) them together for perfectly uniform color.

Coverage by Paint Type

Not all paints are created equal when it comes to coverage. Here is a general guide to coverage rates by paint type:

• Interior latex (flat/eggshell): 350-400 sq ft per gallon
• Interior latex (semi-gloss/gloss): 300-350 sq ft per gallon
• Exterior latex: 250-350 sq ft per gallon
• Oil-based (alkyd) paint: 350-450 sq ft per gallon
• Primer (latex): 200-300 sq ft per gallon
• Primer (shellac-based): 150-200 sq ft per gallon
• Ceiling paint: 350-400 sq ft per gallon
• Cabinet and trim paint: 300-350 sq ft per gallon

These are averages based on smooth, previously painted surfaces with standard application thickness. First coats on raw or porous surfaces will always require more paint than subsequent coats. Professional painters typically plan for 10 to 20 percent more paint on the first coat compared to the second coat.

Frequently Asked Questions