Paint Quantity Calculator

Paint Quantity Formula

The paint quantity formula every paint store teaches:

Paint Quantity (gallons) = (Paintable Area x Coats) / Coverage Rate

Coverage rate depends on the surface. Standard values published by Sherwin-Williams, Benjamin Moore, and Behr:

Surface	Coverage per Gallon
Interior smooth drywall	350 sq ft
Exterior primed siding	300 sq ft
Textured wall	250 sq ft
Rough masonry / stucco	200 sq ft
Ceiling flat paint	400 sq ft
Split-face block / brick	150 sq ft

Paint Quantity by Input Method

This calculator accepts two input styles:

Total wall square footage is best when you already measured the room on a floor plan or walked the walls with a laser distance meter. Enter the number and go.

Room dimensions works when you just need the paint quantity for a standard rectangular room. Enter length, width, and ceiling height; the calculator computes perimeter x height as gross wall area, then subtracts openings.

Example: 14x16 Master Bedroom

• Length 14 ft, width 16 ft, ceiling 8 ft
• Perimeter: (14+16+14+16) = 60 ft
• Gross wall area: 60 x 8 = 480 sq ft
• Openings: 1 door (21) + 2 windows (30) = 51 sq ft
• Paintable area: 480 - 51 = 429 sq ft
• Paint quantity: (429 x 2) / 350 = 2.45 gallons
• With 10% waste: 2.70 gallons
• Order: 3 gallons

Three gallons covers the room at 2 coats with a small amount left over for touch-ups.

Paint Quantity for Common Rooms

Room	Area	Gallons (2 coats, no openings)
10 x 10 bedroom	320 sq ft	2
12 x 14 bedroom	416 sq ft	3
14 x 16 master	480 sq ft	3
16 x 20 living room	576 sq ft	4
10 x 14 kitchen	384 sq ft	3
8 x 12 bathroom	320 sq ft	2

Paint Quantity for Exterior Jobs

A 2,000 sq ft two-story home has about 2,500-3,000 sq ft of exterior wall after deducting windows and doors. At 300 sq ft/gal and 2 coats:

• 2,750 x 2 = 5,500 sq ft total coverage
• 5,500 / 300 = 18.3 gallons
• With 10% waste: 20.2 gallons
• Order: 21 gallons (four 5-gallon buckets plus one gallon)

Buy one 5-gallon bucket at a time. Mix buckets in a clean tub before rolling to eliminate color-batch variation.

Coverage Rate Corrections

Published coverage rates are achievable on ideal surfaces. Real-world paint quantity should account for:

• New drywall: 15-20% more paint; bare drywall is thirstier than primed or previously-painted
• Rough cedar or redwood: 20-30% more paint; grain soaks up primer and first coat
• Stucco or split-face block: double the smooth-wall quantity for the first coat
• Cut-ins and trim: add 1 extra gallon per 1,000 sq ft paintable area for brush work around edges

Primer Is Separate Paint Quantity

Primer has its own coverage rate (200-300 sq ft/gal) and is calculated as a single extra coat. For new drywall or repaint projects where you are blocking stains, add a primer line item: paintable area / 250 = gallons of primer.

Container Sizing

Paint retails in three US container sizes:

• Quart (0.25 gal): covers ~88 sq ft. For trim, touch-ups, or an accent wall under 40 sq ft.
• 1-gallon can: covers 350 sq ft on smooth interior drywall. The default residential size.
• 5-gallon bucket: covers 1,750 sq ft. Saves 20-30% per gallon vs 1-gallon cans.

Buy 5-gallon buckets whenever paint quantity is 3+ gallons. The per-gallon savings pays back a single bucket in one project.

Paint Quantity Tips

• Always measure wall by wall, then add. For vaulted walls, break the shape into a rectangle plus a triangle (base x height / 2).
• Subtract only openings you are not painting. Trim and the inside face of doors are usually painted and should not be deducted.
• Round up to the nearest whole gallon, always. A half-gallon left over is worthless; a quart for touch-ups is gold.
• If you buy two brands or two runs of the same color, mix them in a 5-gallon bucket before rolling. This eliminates subtle color-batch variation that shows up under raking side-light.