Paint Coverage Calculator
Estimate gallons of paint, total cost and paintable surface area for any number of rooms.
Overview
The Paint Coverage Calculator estimates how many gallons of paint you need, how much it will cost, and the total paintable surface for any number of rooms. Buying paint is one of those tasks where the wrong answer hurts in both directions: too little and you run out mid-wall with a colour you cannot perfectly match, too much and you have leftover cans cluttering the garage for years. A few measurements upfront removes both risks.
The calculator works room by room, subtracting standard door and window areas, optionally including ceilings, and multiplying by the number of coats. It returns total surface area, paintable area after subtractions, total area to cover including coats, gallons rounded up, and a total cost when you supply a price per gallon.
How it works
Enter the room's length, width, and height in feet, plus the number of doors and windows and whether you are painting the ceiling. Set a global door and window square footage so the math accounts for openings. Add additional rooms with the plus button; each room contributes to the totals independently and a per-room breakdown is available in a detail panel.
The coverage per gallon defaults to a typical 350 square feet but can be tuned for primers, ceiling paint, or coverage-rated formulations. Gallons are always rounded up, since you cannot buy a fraction of a can.
Examples
- A 12 x 14 x 8 ft bedroom with one door and two windows, two coats, no ceiling.
- A two-room paint job combining a hallway and a stairwell with their distinct dimensions.
- An open-plan space estimated as one large rectangular room, including the ceiling.
- A repaint where you only need one coat over an existing similar colour.
FAQ
Why are doors and windows subtracted?
You do not paint glass or panel doors with wall paint, so removing their area gives a realistic paintable surface.
What coverage per gallon should I use?
350 square feet is a typical wall-paint figure; check the can label, as primers and textured surfaces can drop it well below that.
Does it include trim, baseboards, or doors themselves?
No, it estimates wall and optional ceiling area only. Trim paint is usually bought separately in small quantities.
How accurate is the cost figure?
It multiplies the rounded-up gallons by your price per gallon, ignoring discounts or taxes; treat it as a planning estimate.
Should I buy extra for touch-ups?
A small surplus is wise; rounding up gallons usually leaves enough, but for large rooms consider adding one extra can.