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Calculation details
Planning estimate only. Verify dimensions, waste, coverage, product specifications, and local requirements before purchasing materials.
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What does this calculator estimate?
A 12 x 15 ft room with 8 ft walls has 432 sq ft of wall area, and after subtracting two doors and two windows the paintable surface is about 362 sq ft. Two coats take that to 724 sq ft, which is just over 2 gallons at 350 sq ft per gallon, so buy 3 gallons to cover it fully. Work out your own room in the BoringToolsKit paint coverage calculator.
- Wall area is perimeter times wall height; a 12 x 15 ft room with 8 ft walls is 432 sq ft before openings. (Source: BoringToolsKit calculation methodology)
- Most paint covers about 350 sq ft per gallon, so 724 sq ft of two-coat coverage needs just over 2 gallons. (Source: BoringToolsKit calculation methodology)
- Coverage varies by paint and surface, and primer can change how many gallons you need. (Source: BoringToolsKit calculation methodology)
How this calculator works
Formula
paintable area = wall area − openings; gallons = coats × area / coverage per gallon
Worked example
A 12 x 15 ft room, 8 ft walls, 2 doors and 2 windows: 362 sq ft paintable, 724 sq ft with two coats, about 3 gallons at 350 sq ft per gallon.
Assumptions to verify
- Coverage varies by paint and surface
- Primer may change requirements
- Openings and trim are estimated
Frequently asked questions
Why does paint coverage vary?
Porous walls, color changes, texture, and paint quality can change actual coverage.
Should I include a second coat?
For most interior repaints, planning for two coats is safer unless product guidance says otherwise.
Cite this tool
BoringToolsKit. “Paint Coverage Calculator.” boringtoolskit.com/paint-coverage-calculator/. Free to reference in articles, syllabi, and answer posts with a link.
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