How Much Siding Do You Need?
Siding quantity is measured in squares — one square equals 100 square feet of coverage. Getting the count right before you buy saves two trips to the lumber yard and avoids the nightmare of running short mid-job. Under-order and you risk a discontinued color match; over-order and you're hauling back full cartons. This calculator gets you to the right number, including house wrap, J-channel, and starter strip so you can place one complete order.
Understanding Siding Squares
Siding is sold by the square regardless of material type. Vinyl siding typically comes 2 cartons per square (each carton = 50 sq ft). Fiber cement planks (Hardie board, Allura) come in individual boards — you'll convert square footage to board count based on the plank width and length you choose. Wood lap siding works the same as fiber cement. This calculator gives you the square footage; your specific product's coverage specs handle the board count conversion.
What This Calculator Covers
- Gross wall area — perimeter × height, with optional gable triangles
- Net siding area — gross minus window and door deductions
- Squares with waste — 10% or 15% waste factored in
- House wrap (Tyvek/WRB) — 900 sq ft per standard 9'×100' roll
- J-channel — 12.5 ft pieces to frame all window and door openings
- Starter strip — 12.5 ft pieces for the bottom course
- Nails/fasteners — boxes of 1,000 coil nails (covers ~3 squares each)
- Estimated material cost by siding type
Measuring Your House
Length and width: Measure the outside dimensions of the house footprint at ground level. For a rectangular house, that's two measurements. For L-shapes or additions, break the house into rectangles and add the perimeters together — or just enter the total gross wall area directly if you already have it.
Wall height: For a single-story house, this is typically 9 ft (8 ft ceiling + floor framing). For two-story houses, measure total wall height from the bottom of the first-floor sheathing to the top plate of the second floor — typically 18–20 ft.
Gable ends: A standard gable-roof house has two triangular gable ends. If you're siding those too (not covered by trim boards alone), turn on the gable option and enter your roof pitch. The calculator computes each triangle as ½ × house width × rise.
Materials Needed
Enter dimensions above to see results
Pro Tips
- Always measure wall height from the bottom of the sheathing, not the finished floor — the siding runs all the way down to the foundation
- Order 5% extra panels beyond the waste factor if your color is a special order — matching dye lots is nearly impossible after the fact
- Install house wrap with 6-inch horizontal overlaps, overlapping upper over lower (shingle-style), and tape all seams and penetrations
- Leave a 1/4-inch expansion gap at both ends of every vinyl siding panel — vinyl expands significantly in summer heat
- Vinyl siding is installed "loose" — nail through the center of the nail slot, never pull tight, so panels can slide freely
- Use corrosion-resistant fasteners only: hot-dipped galvanized or stainless. Standard steel nails will bleed rust stains through the siding within 2 years
Siding Material Comparison
| Material | Cost/Square | Lifespan | Maintenance | DIY Friendly |
|---|---|---|---|---|
| Vinyl | $80–120 | 20–40 years | Very low (wash annually) | Yes — snap-lock install |
| Fiber Cement (Hardie) | $150–250 | 30–50 years | Paint every 10–15 years | Moderate — heavy, saw dust hazard |
| Wood Lap | $180–280 | 20–40 years | Paint/stain every 5–7 years | Yes — nail and paint |
| Engineered Wood | $100–170 | 25–30 years | Paint every 5–8 years | Yes — similar to wood lap |
Frequently Asked Questions
Q: How many squares of siding do I need?
A: One square = 100 sq ft. Measure house perimeter × wall height for gross area, subtract window and door openings, add 10% waste, divide by 100. A 40×30 ft house with 9 ft walls, 6 windows, and 2 doors needs about 13–15 squares.
Q: How much does vinyl siding cost per square?
A: Vinyl siding materials run $80–120 per square (100 sq ft). Fiber cement (Hardie) costs $150–250 per square. Wood lap runs $180–280 per square. Labor typically adds 100–150% on top of material cost.
Q: What is house wrap and how much do I need?
A: House wrap (Tyvek or similar) is a water-resistive barrier between sheathing and siding. Standard rolls are 9 ft × 100 ft = 900 sq ft. Divide your gross wall area by 900 and round up to get roll count.
Q: What is J-channel and do I need it?
A: J-channel is the trim that frames every window and door opening where siding panels terminate. Each 12.5 ft piece runs along one edge of an opening. Add up all 4 sides of each window and door, add 10%, divide by 12.5 for piece count.
Q: What is a starter strip?
A: The starter strip (starter course) is the first piece installed at the bottom of the wall. It locks the first row of siding at the correct angle and seals the bottom edge. You need enough to run the full perimeter of the house plus 10% for cuts.
Q: How much waste should I add for siding?
A: Add 10% for a simple rectangular house. Use 15% for L-shapes, T-shapes, or houses with many angles and gables. Waste comes from cutting panels around windows, doors, and corners, plus damaged panels during delivery and installation.