onlinecalculator.me

Free online paint calculator

Paint coverage depends on wall area, the number of coats, and how far each gallon spreads. This calculator works out exactly how much paint to buy — including a waste buffer — so.

Gallons needed
— gal
Exact: — gal
Quarts
—
Net area
— sq ft
Gross area (with waste)
— sq ft
About this calculator

How to use

  1. Enter the total wall area in square feet.
  2. Set the number of coats (2 is standard).
  3. Enter the coverage rate from your paint can label (default 350 sq ft/gal).
  4. Adjust the waste percentage (default 10%).
  5. Read the exact gallons, rounded-up gallons to purchase, and quarts.

Formula

net area   = wall area × coats
gross area = net area × (1 + waste% ÷ 100)
gallons    = gross area ÷ coverage per gallon
buy        = ceil(gallons)
quarts     = buy × 4

Worked example

Room with 600 sq ft of wall area, 2 coats, 350 sq ft/gal coverage, 10% waste:

net area   = 600 × 2             = 1,200 sq ft
gross area = 1,200 × 1.10        = 1,320 sq ft
gallons    = 1,320 ÷ 350         ≈ 3.77 gal
buy        = ceil(3.77)           = 4 gallons
quarts     = 4 × 4               = 16 quarts

Buy 4 gallons or 1 full gallon + 3 quarts for a tighter purchase.

Notes

  • Ceilings are typically excluded from wall area — measure them separately if painting.
  • Primer has lower coverage than finish paint (often 250–300 sq ft/gal) — run a separate calculation for priming.
  • Paint sold in quarts covers roughly 87–100 sq ft per coat; use quart mode for small accent walls.

Frequently asked

How much wall area does one gallon of paint cover?
Most interior paints cover 350–400 sq ft per gallon per coat on smooth, primed walls. Rough, porous, or dark surfaces may only yield 250–300 sq ft. The default in this calculator is 350 sq ft/gallon — edit it to match your paint's label.
How do I calculate wall area for a room?
Add up the area of each wall: height × width for each wall, then subtract door and window openings (a standard door is about 21 sq ft, a window about 15 sq ft). For a quick estimate, the calculator accepts a total area directly.
Why does the calculator show two gallon numbers?
The exact figure is what the math says; the rounded-up figure is what you'd actually buy, since paint is sold by the gallon. If the exact amount is 3.1 gallons, you'd buy 4. The quart count converts the rounded-up gallons to quarts (× 4) for smaller top-up purchases.
How many coats of paint do I need?
Two coats are standard for most color changes and new drywall. One coat works for touch-ups or when using paint-and-primer-in-one over a similar color. Going from light to dark (or dark to light) may need three coats.
What waste percentage should I use?
10% is a good default for experienced painters. Add 15% for complex rooms with lots of corners and cut-in work. Drop to 5% if you're spraying a large, open wall.