Paint Requirement Calculator

How the Paint Requirement Calculator Works

The paint requirement formula is:

Gallons = (Paintable Area x Number of Coats) / Coverage Rate

Where:

• Paintable area = gross wall area minus standard doors (21 sq ft each) and windows (15 sq ft each)
• Number of coats = 2 for most repaints, 3 for dark-to-light color changes
• Coverage rate = square feet a gallon covers on your chosen surface

The calculator adds a waste allowance on top (default 10%) for touch-ups and spills, then rounds up to whole gallons because paint is sold in 1-gallon cans or 5-gallon buckets.

Coverage Rates by Surface Type

These are the coverage rates published on 2025 Sherwin-Williams, Benjamin Moore, and Behr data sheets:

Surface Type	Coverage per Gallon
Interior smooth drywall	350 sq ft
Interior mild texture	300 sq ft
Exterior primed siding	300 sq ft
Heavy texture or popcorn ceiling	250 sq ft
Rough masonry or stucco	200 sq ft
Split-face block or brick	150 sq ft

Textured or porous surfaces absorb more paint. First coat on bare masonry often needs 150 sq ft/gal; second coat recovers to 250 sq ft/gal as the surface seals.

Worked Example: 12 ft x 14 ft Bedroom

• Room: 12 x 14 ft with 8 ft ceilings
• Perimeter: 52 ft
• Gross wall area: 52 x 8 = 416 sq ft
• Openings: 1 door (21 sq ft) + 2 windows (30 sq ft) = 51 sq ft
• Paintable area: 416 - 51 = 365 sq ft
• At 350 sq ft/gal and 2 coats: (365 x 2) / 350 = 2.09 gallons
• With 10% waste: 2.29 gallons
• Paint requirement to order: 3 gallons

Three gallons leaves enough for touch-ups over the next few years, which is exactly when a scuff or wall repair will need the same color.

Paint Requirement for Common Room Sizes

At 8 ft ceilings, 2 coats, interior smooth drywall, 1 door and 2 windows subtracted:

Room	Gross Wall Area	Paintable Area	Gallons
10 x 10 bedroom	320 sq ft	269	2
12 x 12 bedroom	384 sq ft	333	2
12 x 14 bedroom	416 sq ft	365	3
14 x 16 master	480 sq ft	429	3
16 x 20 living room	576 sq ft	525	4
10 x 14 kitchen	384 sq ft	333	2

Paint Requirement for an Entire House

Typical interior repaints of a single-story 2,000 sq ft home with 8 ft ceilings, all rooms:

• Gross wall area: approximately 4,500 to 5,500 sq ft
• After door/window deductions: 3,800 to 4,800 sq ft paintable
• At 2 coats and 350 sq ft/gal: 22 to 28 gallons

Order a 5-gallon bucket plus a few 1-gallon cans rather than 25 individual gallons. Five-gallon buckets run 20 to 30% less per gallon.

Exterior Paint Requirement

A 2,000 sq ft two-story home has roughly 2,500 to 3,000 sq ft of exterior wall after subtracting windows and doors:

• At 300 sq ft/gal and 2 coats: (2,750 x 2) / 300 = 18.3 gallons
• With 10% waste: 20.2 gallons
• Paint requirement to order: 21 gallons

At $50/gal that is $1,050 in paint alone, plus primer, caulk, and labor for a pro repaint.

When to Add More Coats

• Dark to light color change: 3 coats, or tinted primer plus 2 top coats
• New drywall: primer plus 2 top coats
• Stain or water damage: stain-blocking primer plus 2 top coats
• Economy paint (under $20/gal): typically 3 coats for coverage

Primer Is a Separate Calculation

The paint requirement above covers top coats only. Primer has its own coverage rate (200 to 300 sq ft/gal). For most repaints over existing paint in the same color family, primer is optional. For new drywall, bare wood, stain spots, or dramatic color changes, calculate primer separately at 250 sq ft/gal.

Tips for an Accurate Paint Requirement

• Measure wall by wall, then sum. For vaulted or angled walls, break into a rectangle plus a triangle (base x height / 2).
• Do not forget closets. A 5 x 7 walk-in with 8 ft ceilings adds 192 sq ft of wall.
• Subtract only openings you will not paint. Trim and the inside face of doors are usually painted and should not be deducted.
• Ceilings are a separate calculation: use ceiling area (length x width) at 350 sq ft/gal.
• Buy in 5-gallon buckets for any project needing 3+ gallons.