Question 1

How much paint do I need for a 12×12 room?

Accepted Answer

For a standard 12×12 ft room with 9 ft ceilings, 1 door, and 2 windows, the paintable wall area is about 382 sq ft after deducting openings. With 2 coats at 350 sq ft/gallon coverage and the default 10% waste allowance, you need approximately 2.5 gallons (2 gal + 2 qt). The theoretical requirement is about 2.18 gallons before waste and rounding.

Question 2

How many square feet will 5 gallons of paint cover?

Accepted Answer

Five gallons of paint will cover approximately 1,750–2,000 sq ft for one coat on smooth, primed drywall at the industry-standard 350–400 sq ft/gallon. For two coats, that drops to 875–1,000 sq ft of wall area. On rough or textured surfaces, expect 1,250–1,500 sq ft per 5-gallon bucket for one coat. Always check your paint can label — coverage rates vary by brand and finish.

Question 3

How do I calculate how much paint I need for a room?

Accepted Answer

Calculate the total wall area: perimeter × ceiling height, where perimeter = 2 × (length + width). Subtract 20 sq ft per door and 15 sq ft per window. Add ceiling area if painting it. Then compute: theoretical paint = (paintable area × coats) ÷ coverage rate. Finally, add your waste/touch-up allowance (10% recommended) and round up to the nearest purchase increment (0.25 gal for US, 1 L for metric). Use the Room mode in our calculator to do this automatically.

Question 4

How much paint do I need for a house exterior?

Accepted Answer

For a typical 40×30 ft house with 20 ft tall walls, 3 doors, and 8 windows: perimeter = 140 ft, wall area = 2,800 sq ft, minus 180 sq ft for openings = 2,620 sq ft paintable. At 350 sq ft/gallon with 2 coats and 10% waste, you need about 16.5 gallons (theoretical ~14.97 gal). Exterior surfaces like stucco or brick absorb more — select the Masonry/Brick finish preset in the calculator for accurate estimates on porous surfaces.

Question 5

How much paint for a ceiling?

Accepted Answer

For a ceiling, measure length × width to get the ceiling area, then divide by your paint's coverage rate. A 12×12 ft ceiling (144 sq ft) needs about 0.5 gallon for one coat at 350 sq ft/gallon with 10% waste, or about 1 gallon plus primer for new drywall. Use the Room mode and toggle 'Include ceiling' — the calculator adds the ceiling area to the total paintable area using the same number of coats and waste allowance you set for the walls.

Question 6

How do I use the paint calculator with known square footage?

Accepted Answer

Select the Known Area mode in our calculator and enter the total paintable square footage you've already measured (from blueprints, a laser measure, or previous estimates). Set your number of coats, coverage rate, and waste percentage. The calculator will compute the theoretical paint required, add your waste allowance, and round up to the nearest purchase quantity — giving you a recommended number of gallons or liters to buy, plus optional primer and material cost.

Question 7

How many square feet does 1 gallon of paint cover?

Accepted Answer

One gallon of paint typically covers 350–400 sq ft on smooth, primed drywall for one coat. On rough or textured surfaces, coverage drops to 250–300 sq ft. Flat/matte finishes cover the most (~400 sq ft/gal), while high-gloss covers the least (~300 sq ft/gal). Exterior paints average 350 sq ft/gal, and masonry paints on brick or block cover only 150–200 sq ft/gal due to absorption. Always check the label on your specific paint can.

Question 8

Do I need primer before painting?

Accepted Answer

Yes, primer is recommended for: new drywall, drastic color changes (dark to light or vice versa), bare wood, and glossy surfaces. Primer seals the surface, improves adhesion, and can reduce the number of topcoats needed from 3 to 2. Our calculator uses separate primer coverage (default 300 sq ft/gal) and a separate primer price so you get an independent estimate. For repaints with similar colors on well-maintained surfaces, a paint-and-primer-in-one may be sufficient.

Question 9

How many coats of paint do I need?

Accepted Answer

Most interior repaints need 2 coats. Use 3 coats when: painting over dark colors with a light shade, using highly pigmented colors (reds, yellows, deep blues), painting new drywall without primer, or using budget/low-coverage paints. Exterior projects typically need 2 coats, with a third recommended for bare wood or high-wear areas. The calculator supports 0–4 coats, with zero available for clearing the estimate.

Question 10

How much does paint material cost?

Accepted Answer

Paint material cost depends on brand and quality. Budget paints: $20–$35/gallon ($5–$9/L). Mid-range: $35–$60/gallon ($9–$16/L). Premium: $60–$100/gallon ($16–$26/L). For a 12×12 room needing ~2.5 gallons, expect $50–$150 in paint material cost. Primer adds $15–$40/gallon. Toggle the Material cost estimate switch in the calculator, set your per-gallon price and currency, and it computes combined paint + primer material cost. For installed labor costs, use our Cost Per Square Foot Calculator.

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