Enter the total length of the walls you are siding, the wall height and the size of any gable ends, and subtract windows and doors. The calculator gives the area in squares, the unit siding is sold and quoted in.
Siding squares calculator
How it works
- Walls = total wall length × wall height
- Gables = number of gables × width × height ÷ 2 (each gable is a triangle)
- Net area = walls + gables − openings
- Squares = net area × (1 + waste %) ÷ 100 (one square is 100 sq ft)
Worked example
A 28 × 42 ft house (140 ft around) with 9 ft walls, two 7 ft high gables and 120 sq ft of windows and doors:
- Total length of walls to side (perimeter): 140 ft
- Wall height (to the eaves): 9 ft
- Number of gable ends: 2
- Gable width (at the base): 28 ft
- Gable height (base to peak): 7 ft
- Windows and doors to subtract: 120 sq ft
- Waste allowance: 10%
The calculator gives:
- Siding to order: 14.70 squares (1,470 sq ft)
- Rounded up: 15 squares (to the next half square)
- Net area: 1,336 sq ft (walls 1,260 + gables 196 − openings 120)
Walls 1,260 sq ft + gables 196 sq ft − openings 120 sq ft = 1,336 sq ft. With 10% waste, 1,470 sq ft, or 14.7 squares.
Material and waste notes
- The waste allowance is your choice. Simple rectangular walls waste less than walls with many openings, dormers or angles.
- Trim, corner posts, J-channel, starter strip and soffit are bought by the piece or linear foot, not included here.
- For a gable, measure the width at the base and the height from the base to the peak.
- Follow the siding manufacturer's instructions for fastening, clearances and overlaps; they affect how much you need.
Frequently asked questions
How many square feet in a square of siding?
100 sq ft.
How do I measure a house for siding?
Measure each wall's length and height, add the triangle area of each gable (width × height ÷ 2), and subtract windows and doors (width × height each).
How much extra siding should I order?
That depends on the house and the product, so the calculator lets you set it. The default is 10%; raise it for walls with many openings, dormers or angles.
Sources
- Vinyl Siding Institute, Vinyl Siding Installation Manual (installation practice: trim, openings and allowances)
- NIST Special Publication 811, Guide for the Use of the International System of Units (unit conversion factors)
Last reviewed: 25 September 2026. The calculation is covered by automated tests with known answers taken from the sources above. Found an error? Please let us know.