Paint Coverage Calculator

Estimate how much wall paint you need in gallons and quarts. Enter room dimensions, subtract standard door and window openings, set your coat count, and adjust the spread rate for your paint type.

Room Details

Room Length

Room Width

Ceiling Height

Number of Doors

qty

Number of Windows

qty

Number of Coats

coats

Paint Coverage Rate350 sq ft/gal

200 sq ft/gal450 sq ft/gal

Live Results

Total Gallons Required

Net Paintable Surface Area

280.00 sq ft

After door & window deductions

Total Quarts Equivalent

Trim & touch-up reference

Total Gross Area

352.00 sq ft

Before deductions

2 coats · 350 sq ft/gal spread rate · Gallons rounded up

How to Use This Calculator

Enter room dimensions. Measure room length, width, and wall height. Include all walls you plan to paint.
Set openings and coats. Adjust door and window counts for deductions. Set the number of coats and coverage rate per gallon.
Review gallon and quart output. Use the gallon count for your primary order. Quarts help fine-tune small touch-up quantities.
Buy slightly over for touch-ups. Keep one quart of each color for future patch work — custom tint matches are hard to reproduce later.

Formula & Example

Professional paint estimators start with the total wall surface area of a room, then subtract the area occupied by doors and windows rather than painting over them. This avoids over-ordering material and matches how painters bid jobs in the field.

This calculator uses industry-standard deduction constants: 21 sq ft per door (a typical 3 ft × 7 ft interior door) and 15 sq ft per window (a typical 3 ft × 5 ft window). These are conservative averages — oversized openings or floor-to-ceiling windows may warrant manual adjustments.

After deductions, the net paintable area is multiplied by the number of coats and divided by the manufacturer's spread rate to determine total gallons. Always round up to the nearest whole gallon when ordering — partial gallons are not sold at retail.

Gross Wall Area = 2 × (Length × Height) + 2 × (Width × Height)

Door Deduction = Number of Doors × 21 sq ft

Window Deduction = Number of Windows × 15 sq ft

Net Area = MAX(0, Gross Area − Door Deduction − Window Deduction)

Paint Volume = (Net Area × Coats) ÷ Coverage Rate

Gallons = CEILING(Paint Volume)

Quarts = CEILING(Paint Volume × 4)

Standard Paint Type Coverage Rates

Spread rates vary by paint sheen, surface porosity, and application method. Use the coverage slider above to match your product label, or reference these typical ranges when selecting a starting point.

Paint Type	Typical Spread Rate	Notes
Primer	200–300 sq ft/gal	Higher absorption on bare drywall or patched surfaces
Flat / Matte	350–400 sq ft/gal	Best coverage; ideal for ceilings and low-traffic walls
Satin / Semi-Gloss	300–350 sq ft/gal	Thicker film build; common for trim, kitchens, and baths

Always verify against the manufacturer's label on the specific product you are purchasing — actual coverage can vary with temperature, humidity, and roller nap thickness.

Worked Example

A 12×12 ft room with 8-ft walls: perimeter 48 ft × 8 ft = 384 sq ft, minus ~60 sq ft for one door and two windows ≈ 324 sq ft net. At 350 sq ft/gal and 2 coats: (324 × 2) ÷ 350 ≈ 1.85 gallons → order 2 gallons.

Frequently Asked Questions

How does multi-coat math affect my gallon count?▾

Each coat requires a full pass over the net paintable surface area. The calculator multiplies net area by the number of coats <em>before</em> dividing by the spread rate: (Net Area × Coats) ÷ Coverage Rate. The result is then rounded up to the nearest whole gallon. For example, 280 sq ft net area at 2 coats and 350 sq ft/gal yields 1.6 gallons — rounded up to 2 gallons. Primer and finish coats may have different spread rates; run the calculator separately for each coat type if they differ significantly.

How do I account for textured or porous walls?▾

Textured surfaces (orange peel, knockdown, popcorn) and highly porous substrates (bare drywall, brick, stucco) absorb more paint and reduce effective spread rate. A common field adjustment is to reduce the coverage rate by 10–25% — for example, lowering the slider from 350 to 280 sq ft/gal for a heavily textured wall. Popcorn ceilings can reduce coverage by as much as 50%. When in doubt, use the manufacturer's worst-case coverage figure from the label.

Does this calculator include ceiling paint?▾

No — this tool calculates wall surface area only. Ceiling paint is a separate takeoff: multiply room length by room width to get ceiling square footage (e.g., a 12 × 10 room has 120 sq ft of ceiling). Add that area to your order separately, or run a second calculation treating the ceiling as a flat surface. Ceiling paint is typically flat or matte finish; use a higher spread rate (350–400 sq ft/gal) on the slider for ceiling estimates.

How many square feet does a gallon of paint cover?▾

Most interior wall paints cover 350–400 sq ft per gallon on smooth, primed surfaces. Textured walls, dark color changes, and porous surfaces may drop coverage to 250–300 sq ft per gallon.

Do I need primer in my paint calculation?▾

Calculate primer separately when covering bare drywall, stained surfaces, or dramatic color changes. Primer typically covers similar square footage to finish paint but may require a full coat on all surfaces.

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