What is the Paint Coverage Calculator?
This tool estimates how many gallons of paint you need to cover your walls. It works for any room or surface by combining your total wall area, the number of coats you plan to apply, and the coverage rating printed on the paint can. The calculator works in any country — just use consistent units (feet and gallons here).
How to Use It
Add up the length of all walls you want to paint and enter it as the total wall length. Enter the wall height, then subtract the combined area of doors and windows you won't paint. Choose how many coats (two is typical for good color depth) and the coverage per gallon — most interior paints cover about 350 square feet per gallon. The calculator rounds up to whole gallons since you can't buy a partial can.
The Formula Explained
First the net paintable area is found: \( A = (\text{Length} \times \text{Height}) - \text{Openings} \). That area is multiplied by the number of coats and divided by coverage per gallon:
$$\text{Gallons} = \left\lceil \frac{A \times \text{Coats}}{\text{Coverage (sq ft/gal)}} \right\rceil$$The result is rounded up so you always have enough paint.
Worked Example
Suppose your room walls total 40 ft long and 8 ft high, with 0 sq ft of openings, painted with 2 coats using paint rated at 350 sq ft/gallon. Net area:
$$A = 40 \times 8 = 320 \text{ sq ft}$$Total painted area:
$$320 \times 2 = 640 \text{ sq ft}$$Gallons:
$$\text{Gallons} = \frac{640}{350} = 1.83$$which rounds up to 2 gallons.
FAQ
How much area does a gallon of paint cover? Most paints cover 300–400 sq ft per gallon on smooth surfaces; rough or porous walls cover less. Check your can's label.
How many coats should I apply? Two coats is standard for even color and durability. Use one coat only for minor touch-ups, or three when going from dark to light.
Should I round up? Yes — buy whole gallons and keep leftovers for touch-ups. This calculator rounds the gallon count up automatically.
