Paint Calculator
Calculate exactly how much paint you need for any room. Enter your dimensions below for instant, accurate estimates.
Results
No calculations yet. Use the form above to get started.
Recommended Purchase
How to Calculate Paint for a Room
Calculating the right amount of paint before starting a project saves time, money, and unnecessary trips to the hardware store. Our paint calculator uses a straightforward formula that professionals rely on: measure the total wall area, subtract openings like doors and windows, multiply by the number of coats, and divide by your paint's coverage rate.
Step 1: Measure Your Room
Start by measuring the length, width, and ceiling height of your room. For rectangular rooms, you need the length of each wall and the floor-to-ceiling height. Use a tape measure for accurate results. Most standard rooms in the United States have an 8-foot ceiling height, while many modern homes feature 9 or 10-foot ceilings.
Step 2: Calculate Total Wall Area
The total wall area is the perimeter of the room multiplied by the wall height. For a rectangular room: 2 × (length + width) × height. For example, a 16 × 13 foot room with 8-foot ceilings has a perimeter of 58 feet and a total wall area of 464 square feet. This is the starting point before any deductions.
Step 3: Subtract Doors and Windows
Deduct the area of all doors and windows from the total. A standard interior door is about 21 square feet (3 × 7 feet). A standard window is roughly 15 square feet (3 × 5 feet). This step prevents over-purchasing and typically saves you 10 to 15 percent on material costs.
Step 4: Factor in Coats and Coverage
Multiply the net area by the number of coats — usually two for best results. Then divide by the paint's coverage rate. Most quality interior latex paints cover 350 to 400 square feet per gallon. Premium or specialty paints may differ, so always check the label. For a 400 square foot room with two coats and 350 sq ft per gallon coverage, you would need about 2.3 gallons.
Understanding Paint Coverage Rates
Coverage rates vary significantly based on paint type, surface texture, and application method. Flat and matte finishes typically cover more area than satin or semi-gloss. New drywall absorbs more paint than previously painted surfaces. Rough textures like stucco or brick can reduce coverage by 20 to 30 percent. Always check the manufacturer's specifications on the paint can for the most accurate coverage information.
Professional Tips for Better Results
Professional painters know that preparation is just as important as the paint itself. Always clean and prime your surfaces before applying the first coat. Use painter's tape for clean edges around trim, windows, and ceilings. Apply paint in a W-pattern with a roller for even distribution, and maintain a wet edge to avoid lap marks. Working in sections and painting from top to bottom gives the most consistent finish.
When purchasing paint, buy all your cans from the same production batch to ensure color consistency. If you are mixing custom colors, have the store mix enough for the entire project in one session. Store leftover paint in a cool, dry place with a tight seal — properly stored latex paint can last up to 10 years for touch-ups and repairs.
Tips & Tricks
Use a primer coat when painting over dark colors to improve coverage and reduce the number of paint coats needed.
Rough or textured walls absorb more paint. Increase your estimate by 15–20% for textured surfaces.
Buy all paint from the same batch to ensure consistent color across your room.
Store leftover paint in a cool, dry place. Properly sealed latex paint lasts up to 10 years for touch-ups.
Results are estimates. Always purchase 5–10% extra material to account for waste, touch-ups, and uneven surfaces.
Formula Used
Paint Needed = (Total Wall Area − Openings) × Coats ÷ Coverage Rate
Total wall area is calculated from room dimensions. Door and window areas are subtracted. The result is multiplied by coat count and divided by paint coverage rate.
Frequently Asked Questions
How much paint do I need for a 12×12 room?
A standard 12×12 foot room with 8-foot ceilings has roughly 384 square feet of wall area. After subtracting a door and two windows, you typically need about 1.5 to 2 gallons for two coats of standard interior latex paint, depending on surface texture and paint quality.
Do I really need two coats of paint?
In most cases, yes. Two coats ensure even color distribution, better durability, and a more professional finish. If you are applying a similar color over an existing coat, one coat may suffice, but two coats are recommended for the best results.
Should I subtract doors and windows from the total area?
Yes. Standard practice is to subtract door and window areas to avoid over-purchasing paint. Our calculator uses standard sizes by default, but you can adjust door and window counts to match your actual room. This step typically saves 10 to 15 percent on material costs.
What does paint coverage rate mean?
Coverage rate is how much area one unit of paint covers in a single coat. Most interior latex paints cover about 350 to 400 square feet per gallon. Premium paints may cover more. Always check the manufacturer label, as rates vary by brand, finish, and surface type.
Should I buy extra paint beyond what the calculator suggests?
Yes, always purchase 5 to 10 percent more than the calculated amount. Extra paint accounts for waste, touch-ups, and uneven surfaces. Keeping leftover paint is also useful for future repairs, so you always have matching color on hand.
Calculation History
No calculations yet. Use the form above to get started.