Paint Calculator

Buying paint is one of those tasks where guessing wrong is expensive in both directions — too little means a second trip to the store mid-project with a risk of a slightly different batch color, too much means unused cans sitting in the garage. The Paint Calculator removes the guesswork by breaking the job into the same steps a professional decorator uses: total wall area, subtract what will not be painted, then divide by how far your specific paint actually spreads. The core idea is coverage rate — every can of paint states how many square feet or square meters one liter or one gallon will cover, usually printed on the label as something like "up to 350 sq ft per gallon" or "10 m² per liter." That figure already accounts for the paint's typical opacity and application method, so the calculator uses it directly rather than trying to model paint chemistry itself. Multiply your paintable area by the number of coats you plan (two coats is the near-universal standard for full color coverage and even sheen), divide by the coverage rate, and round up to a practical purchase quantity. Worked example: a bedroom with four walls measuring 4m × 2.4m, 4m × 2.4m, 3m × 2.4m and 3m × 2.4m totals 33.6 m² of wall. Subtract 3 m² for a door and window, leaving 30.6 m² to paint. At two coats and a coverage rate of 10 m² per liter, that is (30.6 × 2) / 10 = 6.12 liters, which the calculator rounds up to 6.2 liters — enough that you will not be short a few centimeters from the finish line. A common misconception is that "one gallon covers 350 sq ft" means one gallon paints an entire 350 sq ft room. In practice that figure is per coat, and most walls need two coats for solid, even color — skipping this and buying for a single coat is the single most common reason people run out of paint partway through a project. The calculator's "number of coats" field exists specifically to correct for this, and defaulting it to 2 nudges users toward the realistic, industry-standard expectation rather than the misleadingly generous can-label math. Paint type also changes the real-world math in ways a pure geometry calculation cannot capture. Flat and matte finishes tend to spread further per liter than semi-gloss or high-gloss finishes, which are formulated with more resin and often go on in a thinner film for a smoother sheen. Ceiling paint, trim paint and exterior masonry paint all have their own typical coverage figures that can differ meaningfully from a standard interior wall emulsion, which is exactly why the coverage rate is left as an editable field here rather than baked in as a fixed constant — the geometry stays the same, but the coverage number should always come from the can in front of you.