Planning a Fresh Coat of Paint?
Planning a fresh coat of paint for your room instantly transforms your home. However, guessing how much paint to buy often leads to wasted money or extra trips to the store. Use our free paint calculator above to estimate the exact number of gallons you need for your interior wall project.If you are planning a full room refresh, check out our complete step-by-step home decorating guide to streamline your entire project.
Paint Quantity Calculator
Estimated Paint Required:
*Based on standard coverage (~350 sq. ft. per gallon)
How to Calculate Paint Needed for a Room
To calculate the exact amount of paint you need, you must measure your wall dimensions and account for structural features like doors and windows. Follow these four basic steps to measure your room correctly:
Measure Wall Dimensions: Measure the total length and width of the room in feet. Multiply the total distance around the room by the ceiling height to calculate the gross wall area.
Subtract Doors and Windows: Subtract standard cutouts from your gross wall area. Deduct 20 square feet for every standard door and 15 square feet for every average window.
Account for Paint Coats: Multiply your net square footage by the number of coats you plan to apply. Most interior wall projects require two full coats for uniform coverage.
Divide by Paint Coverage: Divide your final square footage number by 350. A standard gallon of wall paint covers roughly 350 square feet of smooth wall space.
Factors That Affect Paint Coverage
While a standard gallon covers roughly 350 square feet, several real-world factors change how much paint your walls absorb.
Wall Texture and Porosity
Unprimed Drywall: Fresh, unprimed drywall acts like a sponge and absorbs significantly more paint during the first coat.
Textured Surfaces: Popcorn walls, brick, or heavy plaster increase total surface area, requiring up to 25% more paint per coat.
Smooth Walls: Previously painted smooth walls yield the highest coverage rate per gallon.
Color Transition and Base Coat
Dark to Light Changes: Painting a light shade over a dark wall requires extra coats or a high-hiding dedicated primer.
Bold Tinted Paints: Bright colors like deep reds, dark blues, or vibrant yellows often need three coats to achieve complete coverage.
Tip: To make sure your chosen paint color complements your furniture and lighting, review our guide on interior design principles before making a final selection.
Frequently Asked Questions
How many square feet does one gallon of paint cover?
One gallon of quality interior paint covers between 350 and 400 square feet on smooth walls. Textured or porous surfaces reduce coverage to around 250 to 300 square feet per gallon.
How many coats of paint do I need for interior walls?
You should apply two coats of paint for almost every interior project. Two coats build proper color depth, conceal surface flaws, and create a durable, washable finish.
Should I buy extra paint for touch-ups?
Yes, always buy an extra quart or gallon from the same color batch. You will need matching paint later to touch up scuffs, wall scratches, or nail holes.