Paint Calculator
By Emiliano · Last updated 2026-09-27
How this calculator works
This calculator determines paint volume by calculating the total wall surface area (perimeter × height) and subtracting the area occupied by openings like doors and windows. The result is divided by the standard coverage rate of 375 sq ft (approx. 35 sq m) per gallon to determine the total paint required per coat.
Formula source: Paint manufacturer coverage specifications and ASTM D523.
Results
How to Calculate Paint
Calculating paint requirements involves determining the total surface area of your walls. For imperial measurements, you measure the length and width in feet, then multiply by the height. A standard gallon of paint typically covers 350 to 400 square feet (32 to 37 square meters). When working in metric, you measure in meters and calculate the area in square meters, noting that one liter of paint covers approximately 10 to 12 square meters. Always account for the number of coats, as primer and multiple finish layers significantly increase the total volume needed.
What Affects Paint Coverage
Several factors influence how much paint you actually need. Surface porosity is critical; raw drywall or unprimed wood (whether 1/2 inch or 12 mm thick) will absorb more paint than a previously painted surface. The color transition also matters; covering a dark wall with a light color often requires a high-quality primer and additional coats. Furthermore, the application method—brush, roller, or sprayer—affects the film thickness. Professional painters typically aim for a dry film thickness of 1.5 to 2.0 mils (0.04 to 0.05 mm) per coat to ensure durability and proper color saturation.
Frequently Asked Questions
Should I buy extra paint?
Yes, it is standard practice to buy 10% extra for touch-ups and future repairs. Paint colors can vary slightly between batches, so having extra from the same batch ensures a perfect match if you need to touch up a wall months later.
Does ceiling height change the math?
Yes. Higher ceilings (e.g., 10 ft or 3 m) increase the wall surface area significantly. A room with 10-foot ceilings needs roughly 25% more paint than the same room with 8-foot ceilings. Our calculator accounts for this automatically using the ceiling height you enter.
How do I handle textured walls?
Textured surfaces have more surface area than smooth walls, so increase your estimate by 15%. Orange peel, knockdown, and heavy textures absorb more paint than smooth drywall. For very rough surfaces like brick or stucco, increase your estimate by 25% or more.