CalcMaterials

Paint Calculator

Find out how many gallons of paint your walls need. Enter the wall area, pick your number of coats, and we apply the standard ~350 sq ft per gallon coverage.

Calculate your materials

What you'll need to buy

  • Interior / exterior paintBy the gallon, in your chosen finishShop
  • PrimerSeals new drywall and big color changesShop
  • Rollers + tray9" roller for walls, mini for tight spotsShop
  • Angled brushCutting in edges, corners, and trimShop
  • Painter's tape + drop clothClean lines and floor protectionShop

Links marked Shop open a retailer search (Home Depot) and are affiliate links — we may earn a commission at no extra cost to you.

How the math works

A room with 400 sq ft of wall, 2 coats, smooth drywall: 400 × 2 = 800 sq ft to cover. With 5% waste: 840 ÷ 350 = 2.4 → buy 3 gallons.

Formula

paintable area = wall sq ft × number of coats gallons = (paintable area × (1 + waste%)) ÷ 350 (use 300 for primer, 250 for textured)

Reference values

Paint coverage reference
SurfaceCoverage per gallon
Smooth interior wall≈ 350 sq ft / gallon
Primer≈ 300 sq ft / gallon
Rough / textured / masonry≈ 250 sq ft / gallon
Smooth trim / doors≈ 400 sq ft / gallon
1 quart≈ 100 sq ft (touch-ups)

Step by step

  1. Measure each wall's length and height and add up the square footage.
  2. Pick your number of coats (2 is standard).
  3. Multiply area × coats, then divide by 350 sq ft per gallon (300 for primer).
  4. Add 5–10% waste and round up to whole gallons.

Waste allowance

Always add a waste factor: more for diagonal, herringbone, or irregular layouts and for trenches in rocky soil. It's cheaper to round up than to pay for a second delivery.

Bags vs. bulk

Bagged material is convenient for small jobs, but loose/bulk delivery is almost always cheaper per unit once you pass roughly 1–3 cubic yards. Compare the per-cubic-yard price before deciding.

Frequently asked questions

How many gallons of paint do I need?

Multiply your wall area by the number of coats, then divide by 350 sq ft per gallon. A 400 sq ft room with 2 coats needs about 800 ÷ 350 ≈ 2.4 gallons — round up to 3.

How much does a gallon of paint cover?

About 350 sq ft per coat on smooth interior drywall. Primer covers around 300 sq ft, rough or masonry surfaces about 250 sq ft, and slick trim up to 400 sq ft per gallon.

How many coats of paint do I need?

Two coats is standard for good coverage and a uniform finish. One coat may do for a refresh in the same color; a dramatic color change can need three.

Do I subtract doors and windows?

For a quick estimate you can ignore them — the extra paint becomes your touch-up buffer. For a tighter number, measure only the wall area you'll actually paint and leave waste at 5–10%.

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