Roofing Calculator
Free online roofing calculator for gable, hip, gambrel, barn, shed, flat, and lean-to roofs. Enter your building dimensions and roof pitch to get roof area in square footage, shingles, bundles, squares, metal roofing panels, rafters, trusses, underlayment, and material cost estimates.
Recommended: 10% gable, 15% hip/gambrel/barn (more cutting at hips and valleys)
1 square = 100 sq ft. Includes shingles only. Range: $80-500/sq depending on type.
How to Calculate Roof Square Footage
Learning how to calculate roof square footage is essential for any roofing project. Follow these steps to accurately measure your roof area, calculate roof squares, and determine the materials you need.
- Measure building dimensions — Measure the length and width of your building at the eaves in feet. Include any overhangs in your measurements. For a 40×30 ft house, your footprint is 1,200 sq ft.
- Determine roof pitch — Roof pitch is the rise in inches for every 12 inches of horizontal run. A 4/12 pitch means the roof rises 4 inches for every 12 inches. Use a pitch gauge or level to measure. To calculate roof pitch in degrees, use the formula: angle = arctan(rise/run).
- Find your pitch factor — The pitch factor converts footprint to actual roof area. A 4/12 pitch has a factor of 1.054. Multiply your footprint by the pitch factor to get the true roof square footage.
- Apply roof type multiplier — Gable and shed roofs use the pitch factor directly. Hip roofs need a hip multiplier (about 1.15). Gambrel and barn roofs need separate calculations for upper and lower slopes.
- Calculate roofing squares — Divide total roof area by 100 to get squares. A 1,200 sq ft footprint with 4/12 pitch gable roof = roughly 1,265 sq ft = 12.65 squares. Add waste and round up.
- Estimate materials — Each square needs 3 bundles of standard shingles. Add underlayment (1 roll per 4 squares), drip edge (perimeter length), and ridge cap shingles. Use our roof square footage calculator above for instant results.
Metal Roof Calculator
Our metal roof calculator helps estimate materials and costs for standing seam, corrugated, and metal shingle roofing. Metal roofing is measured by panels rather than squares. To calculate square foot of roof for metal panels, measure the roof area the same way as shingles, then divide by panel coverage width to get the number of panels needed. Toggle the calculator above to Metal Roofing mode for detailed metal estimates including panel counts, trim pieces, and installation cost.
Metal Roofing Calculator for Material
When using a metal roofing calculator for material, enter your roof area and panel dimensions. Standard panels are 36 inches wide with varying lengths. Our metal roofing calculator accounts for panel overlap (usually 2-3 inches), ridge caps, trim, and fasteners. Standing seam panels typically cost $5-12 per sq ft installed, while corrugated panels range from $3-7 per sq ft.
Standing Seam Metal Roof Cost Calculator
A standing seam metal roof cost calculator considers panel type (snap-lock or mechanical seam), panel gauge (24 or 26 gauge), color, and accessories. Typical standing seam costs range from $8-16 per sq ft installed. Use our metal roof calculator above with your specific project dimensions.
| Metal Roofing Type | Material Cost/sq ft | Installed Cost/sq ft | Lifespan |
|---|---|---|---|
| Corrugated Steel | $1.50-3.00 | $3.50-7.00 | 20-30 years |
| Standing Seam Steel | $3.00-6.00 | $6.00-12.00 | 30-50 years |
| Standing Seam Aluminum | $4.00-8.00 | $8.00-16.00 | 40-60 years |
| Metal Shingles | $3.00-6.00 | $7.00-14.00 | 30-50 years |
| Copper (Standing Seam) | $8.00-15.00 | $15.00-25.00 | 60-100 years |
Roof Pitch Factor Reference
The roof pitch factor converts your building's footprint to actual roof area. Use this table to quickly find the pitch factor for any roof slope. To calculate roof pitch in degrees, take the arctangent of (rise/run). For example, a 6/12 pitch has an angle of approximately 26.6°.
| Pitch | Angle (degrees) | Pitch Factor | Description |
|---|---|---|---|
| 0/12 | 0.0° | 1.000 | Flat roof |
| 1/12 | 4.8° | 1.003 | Minimum slope |
| 2/12 | 9.5° | 1.014 | Minimum for shingles |
| 3/12 | 14.0° | 1.031 | Low slope |
| 4/12 | 18.4° | 1.054 | Standard residential |
| 5/12 | 22.6° | 1.083 | Moderate slope |
| 6/12 | 26.6° | 1.118 | Common residential |
| 7/12 | 30.3° | 1.158 | Steep slope |
| 8/12 | 33.7° | 1.202 | Steep |
| 9/12 | 36.9° | 1.250 | Steep |
| 10/12 | 39.8° | 1.302 | Very steep |
| 11/12 | 42.5° | 1.357 | Very steep |
| 12/12 | 45.0° | 1.414 | Very steep (walkable) |
Roof Type Calculators
Different roof types need different calculation methods. Here is how to calculate roof area for each common type.
Gable Roof Calculator
A gable roof has two sloping sides meeting at a ridge. The pitch factor applies to the entire width. Most common residential roof type.
Hip Roof Calculator
A hip roof has four sloping sides. It requires a hip factor (1.10-1.20) on top of the pitch factor due to additional hip rafters and longer slopes.
Gambrel Roof Calculator
A gambrel roof (barn roof) has two different slopes on each side — a steep upper slope and a shallower lower slope. Common on barns and Dutch colonial homes.
Shed Roof Calculator
A shed roof (lean-to roof) slopes in one direction only. Often used for additions, porches, and modern architecture.
Flat Roof Calculator
A flat roof has minimal slope (0-2/12). Best suited for membrane roofing or rolled roofing materials.
Barn Roof Calculator
A barn roof is similar to gambrel with two distinct slopes. Our barn roof calculator handles both upper and lower pitch inputs for accurate material estimation.
Lean-to Roof Calculator
A lean-to roof is a single-slope roof attached to an existing wall. Our lean-to roof calculator works the same as shed roof calculations.
Common Roofing Calculations
How to Calculate Roofing Squares
A roofing square is 100 square feet of roof area. To calculate roofing squares from square footage, divide the total roof area by 100. For example, 2,450 sq ft of roof area = 24.5 squares. Always round up to the nearest whole square when ordering materials. Our calculator above shows both the exact square count and the number to order with waste included.
Rafter Calculator for Shed Roof
Use our rafter calculator for shed roof to determine rafter length. Rafter length = (width² + rise²)½, where rise = width × pitch/12. For a 30 ft wide shed with 4/12 pitch: rafter rise = 10 ft, rafter length = √(225 + 100) = 18.0 ft per side. Our shed roof rafter calculator includes the overhang for total rafter length.
Roof Truss Span Calculator
Our roof truss span calculator helps determine truss count based on building length and truss spacing. For a 40 ft building with 24-inch spacing: 40 ft × 12 = 480 inches ÷ 24 = 20 trusses. The truss roof calculator above accounts for gable end trusses and girder trusses.
Roof Plywood Calculator
A roof plywood calculator determines how many 4×8 ft plywood sheets are needed for roof sheathing. Divide total roof area by 32 (area of one 4×8 sheet) and add 10% waste. For a 1,265 sq ft roof: 1,265 ÷ 32 = 39.5 sheets + 10% = 44 sheets ordered.
Roof Shingle Bundle Calculator
Standard 3-tab shingles come 3 bundles per square. Each bundle covers approximately 33.33 sq ft. For 14 squares: 14 × 3 = 42 bundles. Architectural shingles may require 4 bundles per square — always check bundle coverage. Our roof shingle bundle calculator above adjusts automatically based on shingle type.
| Material | Coverage | Per Square (100 sq ft) |
|---|---|---|
| 3-Tab Shingles | 33.33 sq ft/bundle | 3 bundles |
| Architectural Shingles | 25-33 sq ft/bundle | 3-4 bundles |
| 15 lb Felt Underlayment | 400 sq ft/roll | 0.25 rolls |
| 30 lb Felt Underlayment | 200 sq ft/roll | 0.5 rolls |
| Synthetic Underlayment | 1,000 sq ft/roll | 0.1 rolls |
| Plywood Sheathing (4×8) | 32 sq ft/sheet | 3.13 sheets |
| Roofing Nails | ~2 lbs/sq | ~320 nails |
Roofing Material Estimation Guide
Accurate material estimation prevents costly delays and waste. Here is a complete guide for calculating roofing materials including shingles, underlayment, drip edge, nails, and accessories.
Roof Waste Calculator
Our roof waste calculator adds the correct waste percentage based on roof type. Gable roofs need 10% waste. Hip, gambrel, and barn roofs need 15% due to extra cutting at valleys, hips, and ridges. Complex roofs with multiple dormers and valleys may need 20% waste.
Roof Coating Calculator
Our roof coating calculator estimates gallons needed for acrylic, silicone, urethane, or EPDM coatings. Enter your roof area, coating coverage rate (sq ft per gallon), and number of coats. Standard acrylic coatings cover 50-80 sq ft per gallon. Silicone covers 40-60 sq ft per gallon. Our calculator handles single or multi-coat applications.
EPDM Roofing Cost Calculator
EPDM (ethylene propylene diene monomer) rubber roofing is popular for flat and low-slope roofs. Our EPDM roofing cost calculator estimates material and installation costs. EPDM membranes cost $0.80-1.50 per sq ft for material, with installation adding $2-4 per sq ft. Total installed EPDM costs range from $4-8 per sq ft.
Roof Drain Calculator
Proper roof drainage is critical. Our roof drain calculator determines the number and size of drains needed based on roof area and local rainfall intensity. For commercial buildings, use the 100-year storm rainfall rate. Standard round drains handle approximately 100-200 sq ft per inch of drain diameter.
Flat Roof Material Calculator
A flat roof material calculator works differently than sloped roofs. Flat roofs use membrane roofing (EPDM, TPO, PVC), modified bitumen, or built-up roofing (BUR). Materials are measured by total square footage without pitch factors. Add 5-10% for overlaps, flashing, and perimeter details.