Interior Finishes Calculator
Paint, flooring, tile, drywall, wallpaper, baseboard trim, carpet and stair stringer calculators - with waste percentages and grout estimates built in.
The interior finishes calculators cover every surface and trim job in a room: paint by gallons, flooring by boxes, tile by piece count plus grout, drywall sheets with screws and joint compound, wallpaper rolls with pattern repeat waste, baseboard trim by linear feet, carpet by square yards with seam math and stair stringer cuts to IRC code. Each tool accounts for the realities of the install - paintable wall area after doors and windows, flooring waste from cuts, tile cuts around fixtures, drywall sheet sizes (4x8, 4x10 or 4x12), wallpaper pattern repeat losses, trim subtraction at door openings, carpet roll width limits and IRC max riser height of 7.75 inches. Use 10% waste for simple straight-lay, 15% for diagonal patterns and 20% for herringbone, chevron or mosaic where every piece is cut on an angle.
Frequently asked questions
A 12 ft x 10 ft room with 8 ft ceilings has about 300 sq ft of paintable wall area after subtracting a door and two windows. Two coats at 350 sq ft per gallon = 1.7 gallons, so buy 2 gallons. Always plan two coats.
A 12x15 ft room is 180 sq ft. With 10% waste = 198 sq ft. If each box covers 20 sq ft, you need 10 boxes. Always round up - you cannot return a partial box and you want extras for future repairs.
A 12x10 room with 8 ft ceilings has 352 sq ft of wall area. Subtract a door and two windows (51 sq ft), add a 120 sq ft ceiling = 421 sq ft total. With 32 sq ft 4x8 sheets and 10% waste, you need 15 sheets. Plus 3 gallons of joint compound, 3 lbs of screws and 2 rolls of tape.
A 12x10 room has a 44 ft perimeter. Subtract a 32 inch door opening (2.67 ft) and you need 41.3 linear feet of baseboard. With 10% waste that is 46 feet, or 3 sticks of 16 ft trim. Crown molding for the same room runs the full 44 ft because it crosses above doorways.
10% is standard for straight-lay flooring or tile in a simple rectangular room. 15% for diagonal layouts or rooms with closets and cutouts. 20% for herringbone, chevron or mosaic where every piece is cut at an angle. For wallpaper, waste depends on pattern repeat - 10% for small repeats, up to 30% for large repeats.
All interior finishes tools
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