How much area does one gallon of paint cover?

As a rule of thumb, one standard gallon of paint covers about 350 to 400 square feet of smooth, primed wall surface. Texturized walls, porous plaster, or unprimed drywall may require up to 30% more paint.

Why is a second coat of paint necessary?

A second coat ensures uniform color depth, hides any roller streak marks, covers micro-pores in the surface, and significantly improves the durability and washability of the painted wall.

Should I deduct doors and windows from my paint calculations?

Yes, standard doors (~20 sq ft) and windows (~15 sq ft) do not get painted with the wall color, so deducting them ensures you do not buy excess wall paint.

Construction Tool

Paint Calculator

Estimate the gallons of paint needed for a room, walls, or ceiling based on custom room dimensions, doors, windows, and planned coats of paint.

Interactive Paint Calculator Workspace

Live Solver

Room Length (Feet)

Room Width (Feet)

Ceiling Height (Feet)

Doors Count

Windows Count

Coats to Apply

Coverage (Sq Ft per Gallon)

Paint Estimation Totals

Net Surface Area366 sq ftexcl. doors & windows

Aggregate Coverage732 sq ftfor 2 coats

Gallons Needed2.09 Galapprox. 3 gallon jars

Quarts Equivalent8.4 Qtsfor detailed purchase

Mathematical Formula & Variables

Equation ModelPaint Gallons = (Total Wall Area - Openings Area) × Coats / Coverage per Gallon

The paint coverage formula calculates the total perimeter of the room multiplied by the ceiling height to get total wall surface area. Subtracts doors and windows, applies the number of paint coats, and divides by the coverage rate (standard is 350 sq ft per gallon).

Variable Definitions

Symbol	Description
Paint Gallons	Total volume of liquid paint needed in gallons
Total Wall Area	Sum of all flat wall surfaces (Room Perimeter × Ceiling Height)
Openings Area	Deducted surface area for doors (~20 sq ft each) and windows (~15 sq ft each)
Coats	Number of individual coats of paint to apply (typically 2 for professional finishes)
Coverage per Gallon	The surface area covered by a single gallon of paint (typically 350 sq ft)

How to Use the Paint Calculator

Enter the Length and Width of the room to calculate the floor or ceiling size.
Input the Ceiling Height of the room to calculate the total wall perimeter area.
Specify the number of standard doors and windows in the room to deduct non-painted spaces.
Input the number of coats you plan to roll on, and select the coverage rating of your paint (350 sq ft is default).
The solver will instantly display the net paint area, total gallons of paint required, and estimate the quarts needed.

Practical Example Calculation

Scenario Context: Painting a living room that is 14 feet long, 12 feet wide, with 8-foot high ceilings. The room has 1 standard door, 2 windows, and requires 2 coats of paint.

Step 1: Calculate room perimeter: (14 + 12) × 2 = 52 feet.

Step 2: Calculate gross wall area: 52 ft perimeter × 8 ft height = 416 sq ft.

Step 3: Deduct openings: 1 door (20 sq ft) + 2 windows (2 × 15 = 30 sq ft) = 50 sq ft deduction.

Step 4: Calculate net wall area: 416 - 50 = 366 sq ft.

Step 5: Multiply by coats: 366 sq ft × 2 coats = 732 sq ft total coverage needed.

Step 6: Divide by standard gallon coverage (350 sq ft): 732 / 350 = 2.09 gallons.

The living room requires approximately 2.1 gallons of paint (which means buying 2 gallons and 1 quart, or 3 full gallons for touch-ups).

Frequently Asked Questions

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