Everyday
Siding Calculator
Figure how many squares, panels, and boxes of siding a house needs, with trim footage and an editable installed-cost estimate.
How it works
Behind the numbers
Start with the walls: enter width and height for each, then add gable triangles as base times height divided by two. Doors and windows are subtracted at an average area you can edit, defaulting to 21 square feet per door and 12 per window, the size of a 3 by 7 foot door and a 3 by 4 foot window.
The net area gets a waste allowance that follows the material: 10% for vinyl, 13% for fiber cement, 15% for wood, 12% for engineered wood. The result converts three ways: squares (100 square feet each, rounded up), individual panels from your per-panel coverage, and boxes from your per-box coverage. Trim is figured separately: starter strip and undersill each run the total wall width, and J-channel runs around every opening.
Cost uses two editable rates per square, one for materials and one for labor. The defaults land near Remodeling's Cost vs. Value 2025 benchmarks of about $1,440 per installed square for vinyl and $1,718 for fiber cement. Everything is a planning estimate, so compare the result with local contractor quotes.
FAQ
Questions, answered
How many squares of siding do I need?
Divide the wall area (minus openings, plus waste) by 100. A 1,500 square foot wall area with 10% waste needs about 16.5 squares, so you buy 17. The calculator does this from your dimensions.
How many pieces of siding are in a square?
A square is 100 square feet of wall coverage. With 12 foot vinyl panels at 8 inch exposure, each panel covers about 8 square feet, so a square takes about 12 to 13 panels. Fiber cement planks at 8.25 inch exposure work out similarly.
What waste percentage should I add for siding?
10% is the standard allowance for vinyl, 12 to 15% for fiber cement, and 15% or more for wood, which needs more trimming around knots and ends. Houses with many gables and corners deserve the high end of the range.
What is J-channel and where does it go?
J-channel is the trim that frames the edges of siding around windows, doors, and corners, hiding the cut ends. This calculator estimates it from the perimeter of your openings, assuming 3 by 7 foot doors and 3 by 4 foot windows.
How much does it cost to side a house?
Remodeling's Cost vs. Value 2025 puts installed siding near $1,440 per square for vinyl and $1,718 per square for fiber cement. A 15-square house therefore runs roughly $21,600 in vinyl or $25,800 in fiber cement before local price differences.