Paint Calculator

How much paint do I need for a 12×12 room?

A 12 ft × 12 ft room with 8 ft walls has a perimeter of 2 × (12 + 12) = 48 ft, so the wall area is 48 × 8 = 384 ft². At the standard 350 ft² per gallon and two coats that is 384 × 2 ÷ 350 = 2.19 gallons — so you buy 3 gallons (paint is always rounded up). Subtract your doors and windows and the calculator updates the math instantly.

One coat or two?

Two coats are the standard for an even, durable finish and are assumed by default. A single coat may be enough when you are repainting the same color over a clean, sealed surface. Always use two coats — plus primer — for new drywall, bare wood, a drastic color change, or covering a stain.

When you need primer

• •New, unprimed drywall — the paper and compound soak up the first coat unevenly.
• •Bare or patched wood, and any raw repair.
• •A drastic color change — primer blocks the old color so you need fewer finish coats.
• •Water stains, smoke or marker — use a stain-blocking primer so they do not bleed through.

Common paint estimating mistakes

• •Buying short. Running out mid-job means a second trip and risks a batch color mismatch — always round up, never down.
• •Ignoring surface porosity. Textured, stucco or bare surfaces cover far less than smooth drywall — pick the right coverage preset.
• •Forgetting the second coat. One coat rarely hides — most jobs need two.
• •Skipping primer on new drywall. The first coat is wasted soaking in; primer is cheaper and seals the surface.

Working in metric? Switch the toggle and the calculator presents litres and square metres natively. As a guide, 350 ft²/gal is about 8.6 m²/L, and one US gallon is 3.79 litres.