How Much Paint Do You Need? Gallons & Cost Calculator

How Much Paint Do I Need for a Wall?

One gallon of paint typically covers 350 to 400 square feet (32 to 37 square meters) with a single coat. Most walls need two coats, so divide your total wall area by 175 to 200 square feet per gallon to estimate paint needed for two coats.

Calculation Tips

• • Measure wall height × width for each wall, then add them together
• • Subtract doors (21 sq ft each) and windows (15 sq ft each) from total area
• • Textured walls may require 10-20% more paint
• • Dark colors over light walls may need 3 coats
• • Always buy 10% extra for touch-ups and mistakes
• • Primer is needed for bare drywall or drastic color changes

Quick Formula

Total Paint (gallons) = (Total Wall Area - Doors - Windows) ÷ 175

Example: Bedroom 12×12 ft with 8 ft ceiling:
• 4 walls × (12 × 8) = 384 sq ft
• Minus 1 door (21) + 2 windows (30) = 333 sq ft
• 333 ÷ 175 = 1.9 gallons (buy 2 gallons)

How Much Paint Do You Need for Different Room Sizes?

Use this quick reference to estimate paint needs for common room sizes. All estimates assume 8ft ceilings, standard doors and windows, and two coats of paint with 350 sq ft per gallon coverage.

Remember to add 10-15% extra for touch-ups and roller absorption. For open-concept rooms, measure each wall individually. Ceiling paint is separate — a standard ceiling takes about 1 gallon per 400 sq ft.

How to Measure a Room for Paint in 5 Steps

Painting contractors measure the same way every time. Run through these five steps and you will buy the right number of gallons — not the ballpark figure that leaves you with half a wall unpainted:

1. Measure each wall's width and multiply by ceiling height. A 12×14 ft room with 8 ft ceilings: (12 + 14) × 2 walls each = perimeter 52 ft × 8 ft = 416 sq ft of wall.
2. Subtract openings by their standard sizes. Doors ≈ 21 sq ft, windows ≈ 15 sq ft. Two doors and two windows take the room to 344 sq ft.
3. Multiply by the number of coats. Two coats over a mid-tone: 344 × 2 = 688 sq ft of coverage to buy for.
4. Divide by real coverage, not the can's best case. One gallon covers 350–400 sq ft on smooth primed walls; rough or heavily textured walls behave closer to 300. At 350: 688 ÷ 350 ≈ 2 gallons.
5. Round up to whole gallons, never partially. Partial batches can drift in color, and touch-ups later need the same batch. One spare quart per room covers drips and future scuffs.

Ceiling: treat it as its own rectangle (length × width) and add 1 coat of ceiling paint at the same coverage rate. The calculator above walks through the same arithmetic with your exact room count, coat count, and per-gallon coverage.

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