What Is the Skirt Board Calculator?
Calculate skirt board length, angle cuts, and material requirements. Skirt boards are the trim that finishes a staircase against the wall: long boards running at the stair's pitch that cover the joint where treads, risers, and the stringer meet the drywall or plaster. They are pure finish carpentry, but they are cut from real geometry: the board's top and bottom edges follow the rise and run of the stair, so the cut angle is the stair angle itself and the length is the hypotenuse of the whole flight. This calculator works out the skirt board length, the cut angle for the miter saw, and how much material to buy, including the extra length for the transition cuts where the skirt meets the baseboard at the bottom and the landing trim at the top. A 1x12 (3/4 by 11-1/4 inches actual) is the standard choice because it is wide enough to cover the stringer face and the tread and riser ends on a typical stair; a 1x10 works only on low-profile builds. Because the skirt goes on before the final paint and caulk, and often before the treads are fully finished, getting its numbers right early keeps the finish schedule clean.
How to Use This Calculator
- Enter the total rise and total run of the stair. The calculator derives the pitch angle and the hypotenuse length of the flight.
- Choose the wall sides that get a skirt board. A stair between two walls needs two boards; a stair with one open side needs one, with the open side finished as an apron or with a capped stringer instead.
- Enter the skirt board width (1x12 is standard, 1x10 for low-profile stairs). The width must cover the stringer face plus the tread and riser ends where they meet the wall.
- Review the board length: the flight hypotenuse plus extra for the transition cuts at top and bottom where the skirt meets baseboard and landing trim.
- Note the cut angle. The skirt's top and bottom cuts are made at the stair's pitch angle, calculated as the arctangent of total rise over total run, not a generic 45 degrees.
- Check the material list. Flights longer than available board lengths (typically 16 feet) need a scarf joint, and the calculator flags where the joint should fall.
