Paint Calculator

What Is Paint? Types, Finishes, and Choosing Right

Use this paint calculator to estimate gallons needed and cost for any room or surface. Paint is a liquid coating applied to surfaces to provide color, protection, and aesthetics. Modern interior and exterior paints consist of four components: pigment (color), binder (the film-forming polymer), solvent (water in latex paint, mineral spirits in oil-based), and additives (thickeners, fungicides, leveling agents). When paint dries, the solvent evaporates and the binder forms a solid film that adheres to the surface.

The two broad categories of paint:

• Latex (water-based) — 90%+ of residential interior and exterior paint sold today; dries in 1–2 hours, easy soap-and-water cleanup, low VOC, flexible film resists cracking; the dominant choice for walls, ceilings, and exterior siding
• Oil-based (alkyd) — historically used for trim and doors; harder, more durable film; extremely long dry time (8–24 hours); requires mineral spirits for cleanup; increasingly replaced by water-based alkyds that match the hardness without the fumes

Paint sheen (finish) is a critical decision that affects both appearance and washability:

• Flat / matte — no sheen; hides surface imperfections well; 350–400 sq ft/gal; best for ceilings, low-traffic walls, and older homes with irregular plaster
• Eggshell — very slight sheen; washable with mild cleaner; 350–380 sq ft/gal; the most popular choice for living rooms and bedrooms
• Satin — subtle pearl-like sheen; good moisture resistance; 300–350 sq ft/gal; excellent for hallways, family rooms, and children's rooms
• Semi-gloss — noticeable shine; highly washable; 300–350 sq ft/gal; standard for trim, doors, windows, and bathrooms
• Gloss — high shine; maximally washable but highlights every imperfection; 250–300 sq ft/gal; used for cabinets, furniture, and accent trim

A note on primer: primer is a separate coat of paint specially formulated to bond with bare or porous surfaces and create a uniform base for finish coats. It is not optional on bare drywall, raw wood, or surfaces changing dramatically in color — skipping primer can require 3–4 finish coats to achieve what primer plus 2 coats would do.

How to Calculate How Much Paint You Need

Calculating paint quantity starts with the total wall area of your room. Measure each wall length, multiply by the ceiling height, and add all four walls together. Then subtract the area of doors (typically 21 sq ft each for a standard 3×7 ft door) and windows (typically 15 sq ft each for a standard 3×5 ft window). The result is your net paintable area.

From there, the formula is straightforward:

Gallons = Wall Area (sq ft) × Number of Coats ÷ Coverage Rate (sq ft/gal)

Always round up to the next whole gallon, since paint is sold in full gallons and quarts. For large rooms or dramatic color changes, add 10% for a safety buffer. If you are also patching holes before painting, consider the drywall calculator to estimate how much material you will need for repairs.

Paint Coverage Rate — What to Expect by Paint Type

The coverage rate printed on a can is typically measured under ideal conditions on a smooth, primed surface. In practice, expect real-world coverage to run 10–20% lower due to surface texture, roller nap thickness, and application technique.

• Flat and matte paints — 350–400 sq ft/gal. Higher solids content means better spread. Best for ceilings and low-traffic walls.
• Eggshell and satin — 300–380 sq ft/gal. The most popular finish for bedrooms and living areas. Offers a slight sheen and is easier to clean than flat.
• Semi-gloss and gloss — 250–350 sq ft/gal. Used for trim, doors, and kitchens. The film is harder and more washable, but applies more thinly.
• Primer — 200–300 sq ft/gal. Primers are thicker and more absorbent; budget more product than for finish coats.
• Textured or unprimed drywall — any paint type will cover significantly less on rough or porous surfaces. Use 250–300 sq ft/gal as your estimate.

If you are adding a decorative texture or patterned surface, our wallpaper calculator may be more useful for estimating coverage on feature walls.

How Many Coats of Paint Do You Need?

The number of coats depends on the starting surface and the color change involved. For most interior repaints over an existing similar color, two coats produce full, even coverage. Here are common scenarios:

• Same color refresh — one coat is sometimes enough if the existing paint is in good condition. Two coats gives a more consistent result.
• Color change (light to medium) — two coats. Use a tinted primer if jumping more than two shades.
• Dark to light (e.g., red to white) — two to three coats, plus a tinted primer to block the dark undertone. Skipping primer can require four or more finish coats.
• New construction or bare drywall — always prime first, then two finish coats. Bare drywall is extremely porous and will show flash (uneven sheen) without primer.
• Ceiling paint — one thick coat of ceiling-specific flat white is usually sufficient for repaints. New construction needs two.

Using a premium paint-and-primer-in-one product can reduce the total number of coats on already-painted surfaces in good condition — but it is not a substitute for primer on bare drywall or dramatic color changes.

Paint Cost Estimates — What to Budget

Interior paint prices vary widely by brand and finish. Here are typical retail price ranges as of 2026:

• Budget / contractor-grade latex — $20–$30/gallon (flat or eggshell). Good for rental units or utility spaces.
• Mid-range interior latex — $35–$55/gallon. Brands like Behr Premium Plus, Sherwin-Williams Emerald, and Benjamin Moore Regal Select fall here. Best value for most homeowners.
• Premium / designer paint — $60–$100+/gallon. Brands like Farrow & Ball or Fine Paints of Europe. Excellent hide and durability, but diminishing returns for standard rooms.
• Primer — $20–$40/gallon. Always use the correct primer for your substrate (drywall, wood, or masonry).

For a standard 12×12 room with 8-foot ceilings, budget $70–$150 for materials (paint + primer), depending on brand. Larger rooms or multiple coats of premium paint can push this above $200 before any labor costs.

Interior vs. Exterior Paint — Key Differences

Interior and exterior paints are formulated for completely different environments. Using the wrong type leads to premature failure and wasted money. If you are also replacing exterior siding as part of a larger renovation, use our siding calculator to estimate the number of panels or squares needed before budgeting for paint.

• Interior paint is formulated for low VOC emissions, easy cleaning, and resistance to scrubbing. It is not designed to handle UV exposure or temperature swings, and will crack and peel outdoors within a year.
• Exterior paint contains UV-resistant resins, mildewcides, and additives that allow the film to flex with temperature changes. It off-gasses more fumes and should not be used indoors in occupied spaces.
• Coverage rates differ — exterior paint typically covers 250–350 sq ft/gal because it is applied to more textured surfaces (wood siding, brick, stucco). Use a dedicated exterior paint calculator or adjust the coverage rate in the calculator above for outdoor projects.
• Sheen matters more outdoors — satin and semi-gloss are preferred for exterior trim and siding because they shed water better and are easier to clean than flat finishes.