Roof Width Calculator | Verified Formulas for Contractors

Important Professional Disclaimer

This calculator provides estimates based on standard roof geometry and should be used for planning purposes only.

Results are mathematical estimates based on simplified assumptions
Actual requirements may vary due to site conditions, material variations, and local building codes
Always verify calculations with on-site measurements and consult local building authorities
For complex roof designs or critical projects, consult with licensed professionals
The tool assumes standard construction practices and may not account for all real-world variables

Use these estimates as a starting point for your planning, not as final construction specifications.

Measurement Units:

Feet & Inches

Meters

Select Roof Type:

Gable

Hip

Shed

Gambrel

Mansard

Flat

Building Width: Enter in feet (short side of building)

Width must be greater than 0

Building Length: Enter in feet (long side of building)

Length must be greater than 0

Roof Pitch (rise/12): Example: 6 for 6/12 pitch (6" rise per 12" run)

Pitch must be between 0 and 24

Overhang (each side): Enter in feet (extends beyond wall on EACH side)

Overhang cannot be negative

Rafter Spacing (on center):

12"

16"

24"

Custom spacing in inches (12-48")

Spacing must be between 12 and 48 inches

Formula: CEIL(Total Roof Length ÷ Spacing) + 1 = Rafters per side

Gable Roof Diagram

GABLE ROOF
CONTRACTOR DIAGRAM

Pitch Factor: 1.05 | Angle: 18.43° | Spacing: 16"

Limitations & Important Notes

This tool provides estimates for standard roof geometries with regular shapes
Complex features like dormers, valleys, or irregular shapes require manual adjustments
Results assume consistent roof pitch and symmetrical building dimensions
Material waste, cutting allowances, and local code requirements are not included
For mansard and gambrel roofs, standard industry proportions are used
Flat roof calculations include minimum 2% drainage slope as per IBC recommendations
Always verify critical dimensions with on-site measurements before ordering materials
Consult with structural engineers for load-bearing requirements and local building codes

Professional Roof Estimates

Roof Type: Gable | Unit: feet | Spacing: 16" OC | Overhang: 1.00 each side | Pitch Factor: 1.05

Note: These are estimates based on mathematical formulas. Always verify with on-site measurements and consult local building codes.

Building Dimensions

30.00 × 40.00

feet (excluding overhangs)

Overhang: 1.00 each side

Total Roof Dimensions

32.00 × 42.00

feet (including overhangs on ALL sides)

✓ Area calculations use total dimensions including overhangs

Rafter Length Estimate

16.87

feet (including overhang)

Formula: (Width/2 + Overhang) × √(1 + (Pitch/12)²)

Total Roof Area Estimate

1,416.70

square feet (using total roof dimensions)

✓ Formula accounts for total dimensions including overhangs

Ridge Length Estimate

40.00

feet

Total Rafter Material Estimate

1,113.12

linear feet (16" spacing)

Estimate rafters needed: 66 (Formula: CEIL(Total Length/Spacing) + 1)

Rafters per side: 33

Fascia Length Estimate

151.46

feet (Eaves + Rakes)

Eaves: 84.00 ft

Rakes: 67.46 ft

Formula: Eaves = 2×Total Length, Rakes = 4×Rafter Length

Roof Pitch Information

4/12

Angle: 18.43° | Factor: 1.05

Professional Verification Notes:
1. ✓ Area calculations use total roof dimensions including overhangs
2. ✓ Rafter count formula accounts for proper spacing requirements
3. ✓ Hip rafter formula verified for accurate 3D geometry
4. ✓ All calculations based on mathematically checked formulas

📚 How to Use This Professional Tool

Enter building width (short side)

Enter building length (long side)

Enter roof pitch as rise/12 (e.g., 6 for 6/12)

Enter overhang (extends beyond wall on EACH side)

Select rafter spacing (16" recommended)

Click Generate Roof Estimates for professional calculations

Verify estimates with on-site measurements and local codes

✓ This tool provides reliable estimates using mathematically verified formulas for standard roof geometries.