Paint & Surface Material Calculator
Calculate exact wall surface area, paint gallons/liters required, coat multipliers, window/door deductions, and project cost.
~21 sq ft each
~15 sq ft each
2 coats recommended
Optional cost estimate
Net Wall Area
396.0 ft²
Excludes doors/windows
Deductions
-72.0 ft²
2 doors, 2 windows
Recommended Buy
3 Gallon(s)
Rounded up for waste
Est. Paint Cost
$135.00
At $45/gal
What is Paint & Surface Material Calculator?
This paint calculator estimates wall and ceiling area, then divides the paintable surface by coverage. A common planning value is about 350 square feet per gallon, or roughly 10 square meters per liter, but the paint label takes priority. Measure length, width, and wall height; count doors and windows; choose coats; and include the ceiling only if needed. For a 12 by 12 foot room with 8 foot walls, four walls cover about 384 square feet before openings, so two coats need roughly 2.2 gallons at 350 square feet per gallon. Textured, porous, dark, or unprimed surfaces need extra paint.
Use the result as a buying estimate and check the paint label for its actual coverage before purchasing.
Measure a room before buying paint
Measure floor length and width, then wall height. For a rectangular room, wall area is twice the sum of length and width multiplied by height. Enter doors and windows separately because the calculator deducts standard opening sizes. Large windows or double doors need a manual adjustment when planning your purchase.
The imperial default is 350 square feet per gallon for one coat. The metric default is 10 square meters per liter, a separate rounded planning rate. Use the coverage printed on your paint instead of assuming every product covers equally. Texture, porous surfaces, and major color changes can increase consumption.
A 12 by 12 foot room with 8 foot walls has 384 square feet of walls before deductions. Two coats at 350 square feet per gallon need about 2.19 gallons. Round up to 3 one-gallon cans if buying only that size. Doors and windows reduce the estimate; painting the ceiling adds 144 square feet per coat. Budget primer separately, follow product instructions on coats and drying times, and reserve some matching paint for touch-ups.
How to Use the Paint & Surface Material Calculator
- 1Select your preferred measurement unit system (Imperial feet/gallons or Metric meters/liters).
- 2Enter room dimensions: Length, Width, and Wall Height, and toggle whether to include the ceiling.
- 3Specify the number of doors (deducting 21 sq ft / 2 m² each) and standard windows (deducting 15 sq ft / 1.4 m² each).
- 4Set the number of paint coats (default 2) and coverage rate to view total cans needed and estimated material expenditure.
Formula & Calculation Logic
Calculates architectural surface enclosure area, deducts standard door/window portals, and divides by manufacturer square-foot coverage ratings.
Gross_Area = 2 * (L + W) * H (+ L*W if ceiling) | Net_Area = Gross_Area - (Doors*21 + Windows*15) | Gallons = (Net_Area * Coats) / CoveragePaint & Surface Material Calculator Frequently Asked Questions
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