Paint coverage is the area in square feet that one gallon of paint will cover. On residential interior walls, a gallon covers roughly 350 square feet with a single coat. On fresh, unpainted drywall, coverage drops to 250 square feet because the drywall absorbs paint. Most interior projects require two coats, and deep colors or saturated finishes often require three.
The calculation
Gallons needed = (total wall area × number of coats) ÷ coverage rate per gallon
Start with your total interior wall surface area (length × height of each wall, summed). Multiply by the number of coats. Then divide by the coverage rate for your paint type and surface condition.
Typical coverage rates for residential interior paint:
- Finished walls (previously painted, smooth): 350 SF per gallon
- New drywall, first coat (primer or paint): 250 SF per gallon
- New drywall, second coat: 300 SF per gallon
- Ceilings (smooth): 400 SF per gallon
- Trim and wood (semi-gloss): 250 SF per gallon
Ceilings have better coverage than walls because the surface is flat and horizontal, allowing paint to spread evenly. Trim and wood have lower coverage because the surface is rough, has multiple sides (edges absorb paint), and semi-gloss paint is heavier-bodied than flat or eggshell wall paint.
Worked example: 926 Stratford
The 1,784-square-foot Sweetwater, TN build has approximately 200 linear feet of interior wall perimeter at 9-foot ceiling height.
Wall area: 200 lf × 9 ft = 1,800 SF per side. Since you paint both sides of many interior walls: 1,800 × 2 = 3,600 SF of wall surface.
But not all interior walls are painted on both sides. Walls bordering the exterior are painted only on the interior side. Walls isolating the garage or mechanical spaces might be primed but not painted. A reasonable estimate for 926 Stratford is 4,000 to 4,500 SF of wall area to be painted.
Ceiling area: 1,784 SF
Assuming two coats of paint on all walls (new drywall) and one coat on ceilings:
Wall paint: 4,250 SF × 2 coats ÷ 300 SF per gallon (second coat is better than first) = 28.3 gallons
Ceiling paint: 1,784 SF ÷ 400 SF per gallon = 4.5 gallons
Primer (on walls only): 4,250 SF ÷ 250 SF per gallon = 17 gallons (budget this separately if using dedicated primer; some builders use paint-and-primer-in-one, which simplifies the count)
Trim: Estimate 600 linear feet of trim (baseboards, door frames, window frames, crown molding). Trim paint: 600 lf ÷ 600 SF per gallon = 1 gallon. (Trim coverage is per linear foot; assume 1 SF per linear foot on average.)
Total for 926 Stratford: 17 (primer) + 28 (wall topcoat) + 4.5 (ceiling) + 1 (trim) = 50.5 gallons
Coverage factors and when they drop
| Condition | Coverage Rate | Reason |
|---|---|---|
| New drywall, first coat | 250 SF per gallon | Drywall absorbs paint; thirsty surface requires heavy application |
| New drywall, second coat | 300 SF per gallon | First coat has sealed the surface; less absorption |
| Previously painted smooth wall | 350 SF per gallon | No absorption; paint spreads easily |
| Flat ceiling | 400 SF per gallon | Horizontal application; gravity helps spread paint |
| Textured ceiling or wall | 200–250 SF per gallon | Texture absorbs paint and increases surface area |
| Deep or dark color (any surface) | 250–300 SF per gallon | Requires 3 coats or heavy application; 1 gallon covers less |
| Semi-gloss or high-gloss (trim) | 250 SF per gallon | Thicker, heavier-bodied paint spreads less far |
Primer versus paint-and-primer-in-one
Most builders use dedicated primer on new drywall, then apply two coats of finish paint. Primer is cheaper and seals drywall effectively. Paint-and-primer-in-one combines both, reducing the number of coats from three (one primer plus two paint) to two, but coverage is lower and the finish is not quite as durable. If you use paint-and-primer-in-one, apply it at first-coat coverage rates (250 SF per gallon) and plan on a second coat to match the finish of dedicated primer plus two topcoats.
Color and saturation: when you need 3 coats
Light, neutral colors (whites, light grays, soft beige) typically need only two coats. Deep or saturated colors (navy, burgundy, forest green, saturated gray) often require three coats to achieve even coverage and hide the substrate. Budget the extra coat if the design includes any dark or bold colors. On the 926 Stratford example, if the master bedroom is painted a deep blue, add another gallon to the wall paint budget.
Application method waste
Brush and roller application wastes 5 to 10 percent of paint (left in the roller, on the brush, on drop cloths). Spray application wastes 15 to 20 percent, because overspray and spray-bounce land outside the target area. If your project uses spray, order 15 to 20 percent extra paint beyond the calculated gallons.
On the 926 Stratford example, if walls are brushed and rolled: 50.5 gallons × 1.07 (7% waste) = 54 gallons. If walls are sprayed: 50.5 × 1.15 (15% waste) = 58 gallons.
Inputs explained
Total wall area. Measure the perimeter of rooms and hallways you will paint, multiply by ceiling height, and sum. Do not subtract for doors or windows; the area they occupy is negligible and hangers benefit from the extra paint for touch-ups.
Ceiling area. Total horizontal ceiling area in square feet. If you have vaulted or tray ceilings, measure the actual surface area, not just the horizontal footprint.
Coat count. New drywall almost always needs primer plus two topcoats (three total). Repaint or walls with existing paint might need only two coats. Decide before calculating.
Surface condition. New drywall is absorbent and requires lower coverage rates than finished walls. Textured surfaces (popcorn, sand, orange-peel) absorb paint and reduce coverage. Gloss or semi-gloss on trim spreads less far than flat or eggshell on walls.
Color depth. Light and neutral colors are standard coverage. Deep, saturated, or bold colors require extra coats or heavier application. Ask your painter before locking a dark-color interior.
Trim, baseboards, and specialty items
Trim paint is typically semi-gloss or satin finish and is a separate line item. Budget 1 gallon of trim paint for every 600 linear feet of trim (baseboards, door frames, window frames, crown molding, etc.). Specialty items like garage interiors, mechanical rooms, and utility closets often use cheaper contractor-grade paint or primer sealer, not finish paint.
Exterior paint is a separate calculation. Exterior paint coverage varies by surface (wood, vinyl, concrete, brick) and is typically 250 to 300 SF per gallon. Exterior work also requires caulk, primer for any bare wood or patched areas, and often a second topcoat for UV and moisture protection. Budget these separately from interior paint.
Sundries and supplies
Paint application requires drop cloths, masking tape, brushes, rollers, roller covers, paint trays, and cleanup supplies. These typically run $50 to $100 per project depending on size and crew experience. Include them as a separate line item.
Material cost ranges
| Material | Cost per Gallon | Notes |
|---|---|---|
| Interior primer (standard PVA) | $12–$20 | Budget grade; adequate for new drywall |
| Interior primer (acrylic or shellac-based) | $20–$35 | Better hide and stain-blocking; use on problem surfaces |
| Interior paint (flat or eggshell, standard brands) | $20–$35 | Contractor-grade; common in residential work |
| Interior paint (premium brands, low-VOC) | $35–$55 | Better durability and environmental profile; visible on walls |
| Trim paint (semi-gloss or satin) | $25–$45 | Thicker than wall paint; more durable on high-touch surfaces |
| Paint-and-primer-in-one | $25–$40 | Reduces coats; not a true replacement for primer and paint |
| Exterior paint (acrylic latex) | $25–$50 | Must be exterior grade for UV and moisture |
| Drop cloth, tape, brushes, rollers (per project) | $50–$100 | Consumables; varies by crew size and reusability |
Common mistakes
Using same coverage rate for primer and paint. Primer is thinner and covers more area than topcoat. Budget primer at 300 to 350 SF per gallon, and paint at 250 to 350 depending on surface condition.
Forgetting the primer coat. Many builders calculate only the two topcoats, then the crew shows up to prime and realizes the budget has no paint. Budget primer separately, especially on new drywall.
Under-estimating ceiling paint. Ceilings cover a lot of area and are easy to overlook in calculations. Do not skip them.
Not accounting for spray waste. If your painter uses an airless sprayer, order 15 to 20 percent extra. Spray is faster but less efficient by volume.
Choosing dark colors without a third coat in the budget. Navy, forest green, deep gray, and burgundy look great but require 3 coats to hide the substrate. Confirm with the designer before locking a dark-color interior.
Forgetting exterior paint. Exterior walls, soffit, fascia, and trim are separate from interior. Budget exterior paint separately and confirm your painter includes all exterior surfaces.
How BuilderGrid wires this into the budget
BuilderGrid’s paint calculator accepts total interior wall area, ceiling area, coat count, surface condition, and color depth. It calculates gallons of primer and topcoat needed, then cross-references the paint cost library to populate material and labor line items for the 926 Stratford seed project. The tool breaks paint into primer, wall paint, ceiling paint, and trim as separate lines, so the superintendent can track paint costs by phase. Exterior paint is a separate calculator. Once locked, the paint line updates if the finishes schedule changes (for example, if a room color is upgraded from a light neutral to a deep blue, the calculator recalculates coat count and gallons instantly). Application method (brush, roll, spray) is selectable, and spray orders automatically add 15 to 20 percent waste.