What This Calculator Does
The Square Feet per Gallon Paint Calculator estimates how many gallons of paint you should buy for a project. It takes the surface area you want to paint, the coverage rating printed on the paint can, and the number of coats you plan to apply, then returns the number of gallons rounded up to the next whole can.
How to Use It
Enter the total wall or surface area in square feet. Add the coverage per gallon — most interior paints cover 300–400 sq ft per gallon (350 is a common average). Choose how many coats you want, usually two for good color depth and durability. The result tells you how many gallons to purchase.
The Formula Explained
The math is straightforward: divide the area by the coverage per gallon to find gallons for a single coat, multiply by the number of coats, then round up because you cannot buy a fraction of a can.
$$\text{gallons} = \left\lceil \frac{\text{area}}{\text{coverage}} \times \text{coats} \right\rceil$$
Worked Example
Suppose you have 800 sq ft of wall, paint that covers 350 sq ft per gallon, and you want 2 coats. The exact requirement is $$800 \div 350 \times 2 = 4.57 \text{ gallons}.$$ Rounded up, you should buy 5 gallons of paint.
FAQ
How much area does a gallon of paint cover? Typically 300–400 square feet on a smooth surface for one coat. Rough, porous, or unprimed surfaces cover less.
Do I need to subtract windows and doors? For small projects you can leave them in as a safety margin. For large jobs, subtract their area for a tighter estimate.
Why round up? Paint is sold in whole cans, so the calculator rounds up to ensure you have enough to finish the job without a second trip to the store.
