How we calculate

Principles

We round up, never down, because running out mid-wall costs more than a leftover quart. We show the intermediate numbers (area, deductions, effective coverage) so you can verify the result by hand. We use manufacturer product data for coverage rates, not marketing copy, and we adjust for surface texture because the number on the can assumes a smooth, primed wall. Where a figure is a typical range rather than a measurement, such as professional labor, we say so next to it.

Paint project planner

A standard door is about 3 × 7 ft (21 sq ft) and a standard window about 3 × 5 ft (15 sq ft). Surface factors: smooth drywall 1.00, light texture 0.90, heavy texture 0.80, new or bare drywall 0.85, brick or masonry 0.65. These reflect the extra paint that texture and porosity absorb, and they line up with the low end of the coverage ranges manufacturers print on their technical data sheets. Coats by color change: similar color 2, light over dark 2 plus primer, deep reds/oranges/yellows 3 plus primer, new drywall 2 plus PVA primer, one-coat touch-up 1. You can override coats manually.

Supplies: one 9-inch roller cover per 2 gallons; roller nap ⅜" for smooth walls, ½" for light texture, ¾" for heavy texture or masonry; one 60-yard roll of tape per 60 ft of room perimeter. Cost: paint at the tier you choose ($25 / $40 / $65 per gallon), ceiling paint at 75% of that, primer at $25 per gallon, and a $45 supplies allowance. Professional estimate: $2–$4 per square foot of wall for labor and paint, which is a typical U.S. range for interior walls in good condition; prep-heavy rooms and high-cost regions run above it. Always get local quotes.

Product presets

Choosing a paint product sets the coverage field from the manufacturer's technical data sheet. Because most sheets give a range (Behr 250–400, Sherwin-Williams 350–400, Benjamin Moore Regal Select 400–450), we start from the midpoint of the range for a smooth, primed wall and then apply the surface factor. Every figure and its source is listed on paint coverage by brand. The coverage field stays editable; the number on your can wins.

Units

The metric toggle converts inputs at 1 m = 3.28084 ft, 1 gal = 3.78541 L, and coverage at 1 m²/L = 40.746 sq ft/gal. Results are always shown in gallons with the litre equivalent; paint in North America is sold by the gallon and the rounding happens there.

Tile calculator

Waste: 10% straight, 12% offset, 15% diagonal or herringbone. Thinset: one 50-lb bag per 90 sq ft (¼" × ¼" trowel). Grout: about 1 lb per 8 sq ft for a ⅛" joint on 12 × 24 tile; wider joints and smaller tiles use more. Installed cost shown as $8–$15 per sq ft, a typical range for floor tile labor and setting materials.

Wallpaper calculator

Strips are the unit that matters. We add 4 inches of trim per strip and a full pattern repeat, because that is the most you can lose aligning a strip. Doors and windows are not subtracted from the strip count; the cut-outs are waste. Professional hanging shown as $45–$90 per roll.

Concrete calculator

The 10% allowance covers an uneven subgrade and spillage. Bag yields are the figures printed by the major bagged-concrete manufacturers. Ready-mix shown at $150–$200 per cubic yard delivered, with a one-yard minimum; poured-and-finished slab at $6–$12 per sq ft.

What we don't do

We don't claim precision beyond the inputs. A calculator cannot see your wall. If your can says a different coverage, type that in. If a contractor quotes outside our range, the contractor is right about your job and we are right about the average. Found a number you disagree with? Tell us and include the data sheet; we update this page when we change a factor.

Last updated 2026-09-03. Method: how we calculate.