🎨 Paint Calculators

How to Calculate Paint Needed for Any Room

Buying the right amount of paint before starting a project prevents the headache of mid-job shortages or excessive leftover cans. The calculation involves measuring the total wall area, subtracting openings (doors and windows), then dividing by the paint's coverage rate — typically 350–400 square feet per gallon for standard interior latex paint.

Core Paint Formulas

Step-by-Step: Painting a Bedroom

A 12 ft × 14 ft bedroom with 9 ft ceilings has 2 doors and 2 windows. How many gallons of wall paint are needed for one coat?

1. Calculate wall area: 2 × (12 + 14) × 9 = 2 × 26 × 9 = 468 sq ft
2. Subtract doors: 2 × 21 sq ft = 42 sq ft (standard door ≈ 3 ft × 7 ft = 21 sq ft)
3. Subtract windows: 2 × 15 sq ft = 30 sq ft (average window ≈ 3 ft × 5 ft = 15 sq ft)
4. Paintable area: 468 − 42 − 30 = 396 sq ft
5. Gallons needed: 396 / 350 = 1.13 → buy 2 quarts + 1 gallon or round up to 2 gallons for two coats

Step-by-Step: Ceiling Paint

The same 12 ft × 14 ft bedroom ceiling:

1. Ceiling area: 12 × 14 = 168 sq ft
2. Gallons: 168 / 350 = 0.48 → 1 quart for one coat, 1 gallon for two coats

Paint Coverage by Type

• Standard interior latex (flat/matte): 350–400 sq ft per gallon
• Eggshell or satin: 350–400 sq ft per gallon
• Semi-gloss (trim, doors): 300–350 sq ft per gallon
• High-hide primer: 200–300 sq ft per gallon (covers more per coat)
• Exterior paint: 250–400 sq ft per gallon depending on surface texture

Rough or porous surfaces (unpainted drywall, brick, textured walls) absorb more paint and reduce coverage by 20–30%. Always check the specific product label for the manufacturer's coverage rate.

Number of Coats

• New drywall: 1 coat primer + 2 coats paint
• Repainting same color: 1–2 coats (1 coat if good coverage, 2 for durability)
• Dramatic color change (light to dark or vice versa): 1 coat primer + 2–3 coats paint
• Trim and doors: 2 coats semi-gloss for durability and washability

Paint Project Tips

• Always buy 10% extra for touch-ups and save leftover paint in airtight containers labeled with room and color.
• Order all paint from the same batch (same dye lot) to avoid color variation between gallons.
• Use a paint calculator before going to the store — returning extra paint is possible at many retailers.
• For ceilings, use flat ceiling paint — it hides imperfections better than wall sheens.
• Trim paint (semi-gloss or gloss) is separate from wall paint — calculate trim length × 6 inches width for a rough area estimate.

Frequently Asked Questions

How many square feet does a gallon of paint cover?

Most interior paints cover 350–400 square feet per gallon with one coat on a smooth, previously painted surface. On raw drywall, brick, or rough surfaces, coverage drops to 250–300 sq ft per gallon because the porous surface absorbs more paint. Always check the specific product's coverage rate on the label.

Do I need to subtract doors and windows from my paint calculation?

Yes, for precise calculations. A standard interior door is approximately 3 ft × 7 ft = 21 sq ft. An average window is approximately 3 ft × 5 ft = 15 sq ft. For rooms with many windows (like sunrooms), subtracting openings can reduce your gallon count by one full quart or more, saving money.

How much does it cost to paint a room?

DIY paint costs typically run $1–$3 per sq ft for materials (paint, primer, tape, rollers, brushes). A 12×14 ft bedroom might cost $50–$120 in materials. Professional painters charge $2–$6 per sq ft for labor, bringing a full bedroom to $200–$600 total. Use the Paint Cost Calculator above to estimate your specific project.

How do I calculate trim paint separately?

Measure the total linear feet of trim (baseboards, crown molding, door and window frames). Multiply linear feet × the trim width in feet to get square footage. For example, 80 linear feet of 4-inch baseboard = 80 × (4/12) = 26.7 sq ft. At 350 sq ft/gallon coverage, one quart of semi-gloss is sufficient for most average rooms.