Roofing & Siding Material Calculator for Illinois Homes
Estimate roofing squares and shingle bundles, underlayment rolls, and siding cartons for a straightforward roof or wall — sized for Illinois freeze-thaw seasons and storm exposure.
Roofing estimate
- Footprint area
- 1,200 ft²
- Pitch factor
- 1.118
- Roof surface
- 1,341.6 ft²
- Adjusted surface (with waste)
- 1,475.8 ft²
- Roofing squares
- 14.76
- Bundles to purchase
- 45
- Underlayment rolls
- 4
This calculator assumes a simple roof with uniform pitch — it does not account for valleys, dormers, hips, flashing, ridge/starter products, or ventilation accessories. Never climb onto a roof to take measurements; use ground-level footprint dimensions or a qualified roofer. Actual bundle yield depends on the manufacturer's product coverage — always confirm against the product label, and verify any work against local code and permit requirements, listed on the Illinois Permit Finder.
This tool provides a planning estimate only. Always verify field measurements, product packaging and supplier yields, manufacturer instructions, and local code and permit requirements before purchasing materials or beginning work. This calculator does not collect or save any personal information — nothing you enter here is stored.
How this is calculated
- Roof surface: footprint area (length × width) × pitch factor (derived from rise per 12), increased by your waste allowance, then converted to 100 ft² "squares."
- Shingle bundles: squares × bundles per square, rounded up to the next whole bundle.
- Underlayment: adjusted roof surface ÷ roll coverage, rounded up to the next whole roll.
- Siding: wall area (perimeter × height) plus any triangular gable area, minus doors and windows, increased by waste, then divided by carton coverage and rounded up to whole cartons.
Worked example
A simple gable roof, 40 ft × 30 ft footprint, 6-in-12 pitch, 10% waste, 3 bundles per square:
- Footprint area = 40 ft × 30 ft = 1,200 ft²
- Pitch factor for 6-in-12 ≈ 1.118
- Roof surface = 1,200 ft² × 1.118 ≈ 1,342 ft²
- Adjusted for 10% waste ≈ 1,476 ft² → 14.8 squares
- Bundles = 15 squares (rounded up) × 3 bundles/square = 45 bundles
Result: plan on roughly 15 roofing squares and 45 shingle bundles for the roof deck alone.
Measuring tips
- Never climb onto a roof to measure it — take footprint dimensions from the ground or from an accurate site/plat drawing.
- Find your roof pitch from the attic (measure rise over a 12 in level run) rather than guessing from the ground.
- Measure wall perimeter and height at ground level with a tape measure or laser measure; measure each door/window opening individually for the total to subtract.
- This tool assumes a simple roof plane and flat wall — valleys, dormers, hips, and complex trim require a professional take-off.