Paint Calculator

Buying too much paint wastes money; buying too little forces a second store trip and risks color-batch mismatches. The standard rule of thumb is 350 square feet of coverage per gallon for one coat on a smooth, primed wall — but real coverage drops with rough surfaces, dark-over-light color changes, and porous drywall.

This calculator uses the wall perimeter (2 × (length + width)) multiplied by ceiling height, then subtracts a typical 50 sq ft for doors and windows. Multiply by the number of coats and divide by 350 sq ft per gallon, then round up — paint is only sold by the gallon or quart.

For best results, plan on two coats for any color change, prime new drywall before painting, and buy 10–15% extra to account for touch-ups over the next few years. Store leftover paint sealed and upside-down to extend shelf life.

Paint coverage is usually quoted as 350–400 square feet per gallon for one coat on a smooth, primed surface. Rough textures (popcorn ceiling, stucco, masonry) can drop coverage to 200 square feet per gallon. Most projects need two coats for proper colour depth and durability, so estimate by multiplying your wall area by two and dividing by the manufacturer's coverage rate. Always buy 10–15% extra for touch-ups and repaints.

Primer matters more than most DIYers realise. Bare drywall, fresh patches and dramatic colour changes (going from dark to light, or to red/yellow/orange) all benefit from a separate primer coat. Self-priming paints work for repaints of similar colours but rarely live up to their marketing claims for the harder cases. Spending an hour and one can of primer saves multiple top coats on difficult jobs.

Paint quality varies enormously. Top-tier paints (Sherwin-Williams Emerald, Benjamin Moore Aura, Farrow & Ball Estate) cost $80–$120 per gallon and cover better, level more smoothly and last 15–20 years. Budget paints at $25 per gallon often need three coats to hide and start showing wear in 5–7 years. For visible interior walls, the higher-priced paint usually wins on total cost when you factor in labour and re-paint frequency.

Tools make as much difference as paint. A high-quality angled sash brush ($15–$25) and a microfiber roller cover ($8–$15) produce dramatically better results than the bargain alternatives. Painter's tape (FrogTape or Scotch Blue) saves hours of cleanup if applied properly. A roller extension pole eliminates the ladder for most ceilings. Add 10–15% to the budget for tools the first time you tackle a room — they pay for themselves on the next project.