Roofing Calculator
Estimate shingles, metal panels or Spanish clay tile, plus underlayment and trim.
| Item | Amount |
|---|---|
| Starter strip | |
| Ridge and hips | |
| Fasteners | |
| Installed tile weight | |
| Underlayment | |
| Drip edge |
Shopping list
How the roofing calculator works
Roofers measure in squares: one square covers 100 square feet. The calculator adds your overhang to the house size, multiplies the footprint by a slope factor for your pitch, and adds your extra percentage for cuts and waste.
- Shingles: squares times 3 bundles (4 for premium), rounded up. Hip and ridge shingles are counted separately at 25 linear feet per bundle.
- Metal panels: roof area divided by the panel's cover width gives the linear feet of panel. Standing seam covers about 16 in, corrugated 26 in and R-panel 36 in. Exposed-fastener panels take roughly 80 screws per square.
- Spanish clay tile: squares times tiles per square, about 114 for a common Spanish profile at about 800 lb per square. Tile is heavy, so confirm the roof structure can carry it.
Slope factors
| Pitch | Factor | Pitch | Factor |
|---|---|---|---|
| 4/12 | 1.054 | 8/12 | 1.202 |
| 5/12 | 1.083 | 9/12 | 1.250 |
| 6/12 | 1.118 | 10/12 | 1.302 |
| 7/12 | 1.158 | 12/12 | 1.414 |
Worked example: 40 ft by 30 ft gable house, 6/12 pitch
With a 1 ft overhang the footprint is 42 x 32 = 1,344 sq ft. Times 1.118 that is about 1,503 sq ft of roof, or 15 squares. With 10% extra you order for 16.5 squares: about 50 bundles of shingles, 5 rolls of synthetic underlayment, 84 ft of starter strip and 2 bundles of ridge shingles. In R-panel metal the same roof takes about 46 panels of 12 ft and 1,300 screws. In Spanish clay tile it takes about 1,885 tiles and adds roughly 12,000 lb to the roof.
Frequently asked questions
How many bundles of shingles are in a square?
Standard 3-tab and architectural shingles run about 3 bundles per square. Some premium dimensional shingles take 4. Check the wrapper for your product.
How much extra should I order?
About 10% for a simple gable, 12 to 15% for hips, and 15 to 20% for roofs with many valleys and dormers. Tear-off and cut-heavy panel layouts can add more.
What is the minimum slope for each material?
Asphalt shingles and most clay tile roofs need about 4/12 or steeper, and the tile maker's rules apply. Metal panels are commonly allowed down to 3/12 with exposed fasteners, and lower with sealed laps. Follow the manufacturer's instructions and local code.
What is not included?
Valley flashing, vents, pipe boots, ice and water shield, hip and ridge tiles for tile roofs, clips for standing seam panels, battens and skylight flashing are not counted. Ask your supplier to confirm a final list.
Estimates only. Panel layout, fastening and structure depend on your product, climate and local building code. Have a licensed roofer confirm before ordering, especially for heavy tile.