Paint Calculator — Estimate Gallons of Paint for Any Room

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How This Material Calculator Works

This calculator uses industry-standard formulas to estimate the quantity of materials needed for your project. It factors in standard waste allowances (typically 5-10% depending on material type) so you purchase enough without significant overbuying. Measurements are based on common product dimensions available at major retailers and building supply stores. For best results, measure your project area carefully and round up to the nearest whole unit when purchasing.

Tips for Accurate Material Estimates

Always measure twice before ordering materials. Account for cuts, corners, and irregular shapes by adding 10% extra for most materials. For concrete and masonry, consider the subgrade preparation and drainage requirements. Check local building codes before starting any project — permits may be required for structural work, fencing over certain heights, or decks above ground level. Buy materials from the same batch to ensure color consistency, especially for tiles, pavers, and paint.

How Many Gallons of Paint for a 12x12 Room?

A 12x12 room with standard 8-foot ceilings has a wall perimeter of 48 feet, so gross wall area is 48 x 8 = 384 square feet. Subtract one standard door (21 sq ft) and one window (15 sq ft) and you are left with about 348 square feet of paintable wall — call it 350. Interior latex paints from Sherwin-Williams, Behr, and Benjamin Moore list coverage of 350-400 square feet per gallon on smooth, previously painted drywall, so one coat takes almost exactly one gallon. Two coats — the standard recommendation for even color and washability — takes 2 gallons. A second window or doorway drops net area to roughly 330 sq ft, and the answer does not change: buy 2 gallons. Painting the ceiling too? That adds 12 x 12 = 144 sq ft, or about 0.4 gallon per coat, so one dedicated gallon of flat ceiling paint covers two coats with a little left over. Total for walls plus ceiling, two coats each: 3 gallons. Rounding up beats a mid-project store run, and leftover paint in a sealed can stays usable for touch-ups for years. If your walls are textured or you are covering a dark color, read the coverage section below before trusting the label number.

Gallons Per Room: Quick Table for 10x10 to 16x20

All figures assume 8-foot ceilings, two coats, one door and one window deducted (36 sq ft total), and 350 sq ft per gallon — the conservative end of most manufacturer labels. | Room size | Net wall area | Two-coat gallons | Buy | |---|---|---|---| | 10x10 | ~284 sq ft | 1.6 | 2 gallons | | 10x12 | ~316 sq ft | 1.8 | 2 gallons | | 12x12 | ~348 sq ft | 2.0 | 2 gallons | | 12x16 | ~412 sq ft | 2.4 | 3 gallons | | 14x16 | ~444 sq ft | 2.5 | 3 gallons | | 16x16 | ~476 sq ft | 2.7 | 3 gallons | | 16x20 | ~540 sq ft | 3.1 | 4 gallons | Two patterns are worth noticing. First, most bedrooms land at exactly 2 gallons for two coats, which is why quart top-ups rarely make sense — a second gallon is the practical unit. Second, once a room needs 4 or more gallons, price out a 5-gallon bucket: as of mid-2026, big-box retailers typically price one at roughly the cost of four single gallons, though promotions vary by brand and season. For taller walls, recompute the gross wall area with your actual ceiling height (perimeter x 9 or x 10), then subtract openings. A 12x12 room with 10-foot ceilings: 48 x 10 = 480 sq ft gross, minus 36 sq ft for a door and window, leaves about 444 net sq ft — 2.5 gallons for two coats, so buy 3.

Texture, Color Changes, and Primer: What Moves the Number

The 350-400 sq ft per gallon label figure assumes smooth, sealed, previously painted walls. Three things routinely break it. Texture: orange-peel, knockdown, and skip-trowel finishes increase real surface area and soak up more paint, cutting coverage to roughly 250-300 sq ft per gallon — plan on 25-30% extra. Color change: covering a dark color with a light one usually takes a coat of gray-tinted primer or a third finish coat; Sherwin-Williams and PPG both publish tinted-primer undercoat systems for exactly this situation. Light-over-light, a quality paint-and-primer-in-one genuinely covers in two coats. Porosity: new drywall, fresh joint compound, and bare wood drink paint. Prime first — PVA drywall primer-sealer covers around 200-300 sq ft per gallon and costs less than finish paint, typically $15-$25 per gallon at Home Depot or Lowe's as of mid-2026. Finish paint runs about $25-$45 per gallon for mid-range lines like Behr Premium Plus or Glidden Essentials and $55-$95 for premium lines like Benjamin Moore Regal Select or Sherwin-Williams Emerald at list price — and both premium brands run frequent 30-40% off promotions, so shelf price is a ceiling, not a floor. The practical rule: budget paint hits label coverage; premium paint often hides in one fewer coat, which can make it cheaper per room.

Ceilings, Trim, and Doors: Finishing the Estimate

Ceiling area is just length times width: 144 sq ft for a 12x12 room, 192 sq ft for a 12x16. At the conservative 350 sq ft per gallon, one gallon of flat ceiling paint covers two coats in any room up to about 13x13. A 14x14 ceiling (196 sq ft, 392 sq ft for two coats) only squeezes into one gallon if the paint hits the 400 sq ft label maximum — so at 14x14 or bigger, buy two. Ceiling paint is worth buying as a dedicated product — it is formulated flatter to hide roller lap marks and typically costs $20-$35 per gallon as of mid-2026. Trim works in linear feet: a typical 12x12 bedroom carries 40-44 linear feet of baseboard plus casings for one door and one window, which unfolds to roughly 60-80 sq ft of paintable surface. A quart of semi-gloss covers 90-100 sq ft, so one quart handles one room's trim in a single coat; two coats or a color change means two quarts, at which point a gallon (which covers 3-4 rooms of trim) is usually the better buy. Interior doors run about 20 sq ft per side — a six-panel door painted both sides adds 40 sq ft, or nearly half a quart per coat. Full-room shopping list for a 12x12 bedroom, two coats everything: 2 gallons wall paint, 1 gallon ceiling paint, 2 quarts trim enamel. That is the estimate this calculator produces when you enter the dimensions above.