Siding Calculator

Siding is the exterior covering material applied to the outside walls of a building to protect against weather and improve appearance. Calculating the correct amount of siding prevents costly over-ordering or the frustration of running short mid-project.

The basic calculation: Total Wall Area = Perimeter × Wall Height Net Siding Area = Total Wall Area - Window Area - Door Area Siding Needed = Net Siding Area × (1 + Waste Factor)

The waste factor accounts for material lost during cutting, fitting around openings, and matching patterns. Standard waste factors range from 10% to 15% depending on the siding type and wall complexity.

Measuring walls: Measure the length of each exterior wall and add them together for the total perimeter. Multiply by the wall height from the foundation to the soffit (eave). For gable ends (triangular sections above the eave), calculate the triangle area: (base × peak height) / 2.

Deducting openings: Measure each window and door, calculate their areas, and subtract from the total wall area. A standard window is approximately 15 square feet. A standard door is approximately 20 square feet. Use actual measurements for accuracy.

Siding types and coverage:

• Vinyl siding: Sold by the square (100 sq ft). Standard panels are 12 feet long and 8 inches of exposure per course. Each square covers 100 square feet of wall area.
• Wood lap siding (clapboard): Coverage depends on board width and overlap. A 6-inch board with 1-inch overlap has 5 inches of exposure, requiring about 20% more material than the net area.
• Fiber cement: Similar to vinyl in coverage, sold in planks or panels. Common exposure is 7-8 inches.
• Board and batten: Requires calculating both the boards and the battens (narrow strips covering the joints).

Additional materials needed: Beyond the siding itself, you will need starter strips, J-channel (for trim around windows and doors), corner posts (inside and outside), soffit material, fascia, and undersill trim. These accessories typically add 15-20% to the total material cost.

Cost factors: Vinyl siding costs $3-$8 per square foot installed. Fiber cement costs $5-$12 per square foot installed. Wood siding ranges from $6-$15 per square foot installed. Labor typically accounts for 50-60% of the total project cost.

Professional tip: Always order 10-15% extra material beyond your calculation to account for waste and future repairs. Matching siding from a different production lot can show visible color differences.