Rafter Calculator

Enter your building dimensions, roof pitch, and rafter spacing to estimate rafter count, lengths, ridge board, and total material cost for a simple gable roof.

Rafter Calculator

Building Width (ft)

Building Length (ft)

Overhang / Eave (in)

Roof Pitch

Rafter Spacing

Rafter Size

Waste Factor (%)

Pricing (edit to match local rates)

2\u00d76 ($/LF)

2\u00d78 ($/LF)

2\u00d710 ($/LF)

2\u00d712 ($/LF)

Ridge Board ($/LF)

Roof Section

Hover for details • not to scale

Total Rafters

31 per side

Rafter Length (each)

14.4 ft

incl. 12" overhang

Total Rafter LF

983 LF

2×8 (incl. 10% waste)

Ridge Board

42 LF

$105.00

Purchase Option	Quantity	Est. Cost
2×6Best value	983 LF	$1,333.96
2×8	983 LF	$1,825.55
2×10	983 LF	$2,317.14
2×12	983 LF	$3,054.51

Most economical: 2×6 at $1,333.96This comparison shows material cost only. Larger rafter sizes may be required based on span, load, and local code requirements. Always size rafters to meet structural needs first, then optimize cost within compliant options.

This is a material estimate for a simple gable roof. Hip roofs, valleys, dormers, and other complex geometries require additional calculations. Always verify rafter sizing and counts with a licensed structural engineer or your local building department.