Paint Coverage Calculator
Achieve professional results and avoid material waste with our interactive painting modeling tool.
Total Material Required
8.00
Gallons (US)
Metric Conversion
30.3 L
Total Coverage
240 m²
Coverage Note
Standard paint coverage is 25-35 m² (300-400 sq ft) per gallon. Textured or porous surfaces may require 20% more paint.
Wall Surface Calc
Total Area = (Perimeter × Height) - (Openings). Subtract roughly 1.5 m² for each standard window.
Paint Coverage Calculator
Calculate the exact number of paint gallons needed for a room. Subtract doors and windows to estimate material costs and prevent wasteful over-purchasing.
Running out of paint halfway through a living room wall is incredibly frustrating, but buying three extra gallons of premium paint you don't need is an expensive waste of money. Guessing the volume required based on the floor size of the room is a fundamentally flawed approach because you aren't painting the floor—you are painting the vertical walls. The Paint Coverage Calculator translates the exact dimensions of your room into total surface area, automatically subtracting doors and windows, to tell you exactly how many gallons of primer and paint to purchase.
Calculating Vertical Surface Area
To paint a room, you must calculate the area of the four walls. The math is: (Length of Wall A + Length of Wall B + Length of Wall C + Length of Wall D) × Height of the Ceiling. This gives you the total gross square footage.
If you have vaulted ceilings or uniquely shaped rooms, the math becomes highly complex. By inputting the length of each individual wall and the ceiling height, the calculator immediately establishes the baseline square footage requiring paint.
The Importance of Subtracting Openings
A massive mistake DIY painters make is forgetting that a large percentage of their wall space is occupied by things that do not get painted: doors and windows. A standard interior door removes about 21 square feet of paintable surface. A large double-window can remove 30 square feet.
If a room has three windows and two doors, failing to subtract those voids means you might accidentally purchase an entire extra gallon of paint. The calculator handles these deductions automatically based on standard architectural sizes.
How to Use the Calculator
First, input the total length of all the walls you intend to paint, followed by the ceiling height. Second, input the total number of standard doors and standard windows in the room.
The tool calculates the Net Paintable Area. Finally, select how many "coats" of paint you plan to apply (drastic color changes or painting over dark walls always requires at least two coats, plus a primer). If you are completely renovating the room and need to buy flooring materials as well, use our Tile & Flooring Calculator next.
Understanding Paint Coverage Rates
The calculator uses the industry-standard coverage rate: One gallon of high-quality interior paint covers approximately 350 to 400 square feet (for a single coat). Primer usually covers slightly less (about 300 square feet) because the bare drywall acts like a sponge and absorbs the liquid rapidly.
If you are painting a highly textured surface (like heavy stucco, brick, or popcorn ceilings), the actual surface area is much higher due to the microscopic peaks and valleys. In these cases, you should expect a gallon to only cover 200 to 250 square feet, and you should manually increase your purchase order.
Expert Insights & FAQs
Quick answers to common questions about this utility.
Should I buy a 5-gallon bucket or individual 1-gallon cans?
If the calculator states you need 4 or more gallons, it is almost always significantly cheaper to buy a single 5-gallon bucket. However, 5-gallon buckets are incredibly heavy (around 60 lbs) and very difficult to pour from without making a mess, so you will need a separate pouring bucket and grid.
Do I need to calculate the ceiling separately?
Yes. Ceilings are usually painted a different color (flat white) than the walls, and ceiling paint is formulated differently to reduce dripping. To calculate the ceiling, simply multiply the Length of the floor by the Width of the floor. That square footage dictates your ceiling paint requirement.
What if I am spraying the paint instead of using a roller?
Airless paint sprayers are incredibly fast, but they waste a massive amount of paint through 'overspray' (paint dust that floats away in the air). If you are using a sprayer, you should add roughly 20% to the final volume recommended by the calculator to ensure you don't run out.