Paint Calculator

Start with the interior single-room flow. Switch modes for a ceiling, a whole exterior, or a primer coat; open advanced options for openings, spray waste, a custom coverage rate, gables, or metric output.

What are you painting?

Interior walls (one room) is the default. Ceiling calculates from length × width. Exterior adds gable triangles. Primer uses PVA drywall-primer coverage at one coat.

Length of the room or footprint in feet. For a ceiling this is one side of the rectangle.
Width of the room or footprint in feet.
Floor-to-ceiling height. Defaults to 8 ft; edit it for 9 ft, 10 ft, or vaulted walls.
Number of coats. Two is the honest default for a repaint; the can's one-coat figure is a best case. Choose 3 only for a drastic dark-to-light change (a tinted primer is usually better).
Smooth walls spread paint at about 350 sq ft/gal (conservative, manufacturer-sourced). Textured, porous, or new-drywall surfaces drop toward ~275. Choose Custom to type your own rate.
Advanced options
Your own spread rate in square feet per gallon. Manufacturer nominal is 350–400 for smooth surfaces (premium 400–450); porous or textured surfaces run lower (~250–300).
Standard doors to deduct at 20 sq ft each. Off by default — many pros do not subtract typical openings.
Windows to deduct at 15 sq ft each. Off by default, like doors.
Extra material lost to overspray when spraying (airless wastes roughly 15–30% more than brushing or rolling). Defaults to 0 for brush/roll.
Triangular gable ends to add (a simple gable roof has 2). Leave 0 for a flat-walled box.
Width of the gable triangle at its base (usually the building width).
Vertical height of the gable triangle from base to peak.
Optional secondary display in litres and square metres. Imperial (gallons / sq ft) stays the primary system.
Buy Buy 2 gallons + 1 quart
Whole gallons 2 gallons
Extra quarts 1 quart
Raw gallons (before rounding) 2.19 gal
Paintable area used 384 sq ft
Coverage rate used 350 sq ft/gal
Coats used 2 coats
Show calculation details
How the purchase maps to cans 2 × 1-gallon cans + 1 × quart
Quart vs gallon A leftover of a quarter gallon or less tops up with one quart; more than that rounds up to the next full gallon, which costs less per unit than buying several quarts. The rounded-up leftover is your touch-up supply.
Coverage basis Based on manufacturer data sheets: Sherwin-Williams SuperPaint PDS 101.11B lists 350–400 sq ft/gal; Benjamin Moore Regal Select N547 lists 400–450 (premium). This estimate used 350 sq ft/gal and the rate is editable.
Advisories None