Interior

Paint, drywall, flooring, tile and trim.

• Drywall calculator — Sheets of drywall for a room, plus the joint compound, paper tape and screws to finish it. Uses the manufacturer coverage tables, not the 0.05 gal/sq ft myth.
• Floor tile calculator — How many floor tiles you need, rounded up to whole boxes, with the waste factor set by your layout and the thin-set bags to go with it. Diagonal and herringbone cost more.
• Laminate flooring calculator — How many boxes of laminate flooring to buy, not just the square footage. Box coverage varies from 16 to 30 sq ft by style, so the count is never the same twice.
• Paint calculator — How many gallons of paint a room needs. Deducts the doors and windows, and prices the first coat separately because bare drywall drinks it.
• Wallpaper calculator — How many rolls of wallpaper you need, counted in strips and adjusted for the pattern repeat. A 25 in repeat on an 8 ft wall throws away a fifth of every roll.