Rafter Length Calculator
Calculate rafter lengths for common and hip rafters. Get accurate measurements for ridge height, birdsmouth cuts, and tail cut angles based on building span, pitch, and overhang.
Common Rafter Results
Rafter Length (no overhang)
13' 4.16"
160.16"
Tail Length (overhang)
1' 1.42"
13.42"
Total Rafter Length
14' 5.57"
173.57"
Ridge Height
5' 11.63"
above wall plate
Plumb Cut Angle
26.6°
from horizontal
Tail Cut Angle
26.6°
plumb cut at eave
Birdsmouth Seat Cut
5.50"
horizontal
Birdsmouth Plumb Depth
2.75"
vertical
Heel Height
5.50"
at wall plate
How to Use This Calculator
Enter the full building span (wall to wall), the roof pitch as rise per 12 inches of run, the overhang or eave length in inches, and the ridge board thickness. Select common or hip rafter to see the corresponding measurements. The calculator deducts for the ridge board and computes birdsmouth dimensions.
Formula Used
Common Rafter: Run = (Span / 2) - (Ridge / 2). Length = Run / cos(pitch angle). Hip Rafter: Hip Run = Run x sqrt(2). Hip Length = Hip Run / cos(hip angle). Ridge Height = Adjusted Run x tan(pitch angle).
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Disclaimer
This calculator is for estimation purposes only. Results may vary based on local conditions, materials, and building codes. Always consult a licensed professional before making decisions based on these calculations. MyContractorTools is not responsible for any errors or omissions.