Ridge Length Calculator
Free Ridge length Calculator for roofing projects. Enter dimensions to get material lists and cost estimates. Free to use with no signup required.
Formula
Gable: Ridge = Length + 2 x Rake; Hip: Ridge = Length - Width
For a gable roof, the ridge runs the full building length plus any rake overhangs at each end. For a hip roof, the ridge is shorter because the hipped ends replace the gable extensions, making the ridge equal to the building length minus the building width. For a Dutch hip, the ridge is intermediate between gable and full hip lengths.
Frequently Asked Questions
How do you calculate ridge board length for a gable roof?
For a simple gable roof, the ridge board length equals the building length plus the rake overhangs on both ends. The rake overhang is the horizontal distance the roof extends beyond the gable end walls. If the building is 40 feet long with 12-inch rake overhangs on each end, the ridge board is 42 feet. For roofs without rake overhangs (flush gable), the ridge board equals the building length. Always add a few inches for trimming when ordering lumber.
How is the ridge length different for a hip roof versus a gable roof?
A hip roof has a shorter ridge than a gable roof because the hipped ends eliminate the need for the ridge to extend the full building length. For a standard equal-pitch hip roof, the ridge length equals the building length minus the building width. If the building is 40 feet long and 24 feet wide, the hip ridge is 16 feet. For a perfectly square building, the ridge length would be zero, creating a pyramid hip roof where all four hip rafters meet at a single peak point.
What size ridge board do I need?
The ridge board should be at least one size deeper than the rafters. For 2x6 rafters, use at least a 2x8 ridge board. For 2x8 rafters, use a 2x10 ridge. This ensures the rafters bear fully against the ridge board. The ridge board is typically 1.5 inches thick (nominal 2x lumber). For engineered ridge beams that carry structural loads, the sizing is determined by engineering calculations based on span, load, and species. Non-structural ridge boards serve as a nailing surface and alignment guide for the rafters.
How much ridge vent do I need?
Ridge vent should run the entire length of the ridge for maximum attic ventilation. The standard recommendation is 1 square foot of net free ventilation area for every 150 square feet of attic floor area, split equally between ridge (exhaust) and soffit (intake) vents. Most ridge vent products provide 18 square inches of net free area per linear foot. For a 40-foot ridge, you would install 40 feet of ridge vent. Always ensure adequate soffit intake venting to match the ridge exhaust capacity for proper balanced airflow.
What formula does Ridge Length Calculator use?
The formula used is described in the Formula section on this page. It is based on widely accepted standards in the relevant field. If you need a specific reference or citation, the References section provides links to authoritative sources.
How do I get the most accurate result?
Enter values as precisely as possible using the correct units for each field. Check that you have selected the right unit (e.g. kilograms vs pounds, meters vs feet) before calculating. Rounding inputs early can reduce output precision.