Interior Finish Calculators for Floors & Walls

A 12x12 bedroom with 8-foot ceilings has approximately 384 sq ft of gross wall area. After deducting one door and two standard windows (~51 sq ft), you have ~333 sq ft of paintable wall surface. Two coats require approximately 1.7 to 1.9 gallons, meaning you should buy two 1-gallon cans. If painting the ceiling white, buy 1 additional gallon.

For standard grid or 1/3-offset brick patterns, order a 10% waste buffer. If laying tiles on a 45-degree diagonal or cutting around curved fixtures and doorways, increase to 15%. Always save at least one unopened carton for future repairs, since dye lots vary between manufacturing runs.

Use a 1/4" x 1/4" square-notch trowel for standard wall tiles up to 8x8 inches. For 12x12 floor tiles, use a 1/4" x 3/8" square notch. For large-format tiles with any edge 15 inches or greater, use a 1/2" x 1/2" square notch or 3/4" rounded notch, and always back-butter the tile.

Measure the perimeter of the room and subtract the width of doorway openings. Add 10% to 15% for 45-degree corner miter cuts, scarf joints, and cutting off damaged ends. For rooms with many short walls or bump-outs, order 8-foot or 12-foot lengths to minimize visible seams.