Paint Calculator
✓ Your estimate
--
Wall Sq Ft
--
Paintable Sq Ft
--
Paint Gallons
--
Primer Gallons
--
Ceiling Sq Ft
⚠ Always round up to the nearest quart or gallon. Confirm coverage rate with your paint brand before purchasing.
What the Result Means
The calculator estimates wall paint gallons based on your room dimensions, coats, and coverage rate. Ceiling paint is listed separately because it is a different product. If you are painting over fresh drywall, see the drywall calculator for sheet and compound estimates first. All interior tools are at the interior calculators page.
How the Calculation Works
Wall Area = 2 x (Length + Width) x Wall Height
Ceiling Area = Length x Width (if selected)
Deductions = (Doors x 21) + (Windows x 15) sq ft
Paintable Area = Wall Area + Ceiling Area - Deductions
Adjusted Area = Paintable Area x Coats x (1 + Waste %)
Paint Gallons = Adjusted Area / Coverage (sq ft per gallon)
Door deduction = 21 sq ft | Window deduction = 15 sq ft
Worked Example
Example: 12 ft x 10 ft room, 8 ft walls, 2 doors, 2 windows, 2 coats, 350 sq ft/gal
1
Wall area: 2 x (12 + 10) x 8 = 352 sq ft
2
Deductions: (2 x 21) + (2 x 15) = 72 sq ft
3
Paintable: 352 - 72 = 280 sq ft
4
2 coats x 5% waste: 280 x 2 x 1.05 = 588 sq ft adjusted
5
Paint gallons: 588 / 350 = 1.68 gallons -- buy 2 gallons
Buying Notes
Assumptions Used by This Calculator
- Door deduction is 21 sq ft per door (standard 3 ft x 7 ft opening).
- Window deduction is 15 sq ft per window (approximate average).
- Coverage rate varies by paint brand, surface texture, color change, and application method.
- Dark-to-light color changes may require primer or additional coats beyond this estimate.
- Textured walls consume more paint than smooth surfaces.
- Ceiling paint is separate -- it is a different product from wall paint.
- Waste factor covers lap waste, roller waste, and touch-up needs.
Frequently Asked Questions
How many gallons of paint do I need for a 12x12 room?
A 12x12 room has about 288 sq ft of wall area (assuming 8 ft ceilings), minus deductions for doors and windows. With 2 coats at 350 sq ft per gallon, you need roughly 1.5 to 2 gallons for walls. The ceiling is 144 sq ft -- about half a gallon per coat.
How much area does one gallon of paint cover?
Most standard interior paints cover 250 to 400 sq ft per gallon on a smooth surface. Textured walls, dark colors, and rough surfaces consume more paint. 350 sq ft per gallon is a solid mid-range estimate for most interior walls.
Should I subtract doors and windows?
Yes -- but it often does not change the gallon count much. Each door opening is roughly 21 sq ft and each window about 15 sq ft. Many painters skip the deduction and use the difference as their touch-up buffer.
Do ceilings need a separate paint estimate?
Yes. Ceiling paint and wall paint are different products with different sheens and formulations. A 12x12 ceiling is 144 sq ft. One gallon covers it in one coat -- plan two coats for a fresh ceiling or color change.
Do I need primer?
Primer is recommended when painting over bare drywall, making a drastic color change, painting over stains, or applying paint to an unpainted surface. For a similar color refresh on previously painted walls, a self-priming paint may be enough.
How many coats of paint should I calculate?
Two coats is standard for most residential jobs. One coat may be enough for a similar color refresh. Three coats may be needed for a dark-to-light change or thin paint on a textured surface.
Should I buy extra paint?
Always round up to the nearest quart or gallon. Keeping a small amount from the same batch is good practice for touch-ups. Touch-up paint from a new batch can dry a slightly different shade.
Disclaimer: This calculator provides estimates only. Actual paint coverage varies by brand, surface condition, and application method. Verify quantities with your paint supplier before purchasing. See all interior renovation calculators.