Guides · Updated October 11, 2026
How to measure a ridge and the hips
Cap is sold by the linear foot of the lines you cover, not by the square footage of the roof. The tape has to follow the shingle, up the slope. A measurement taken flat on the ground, or read off a plan as a horizontal run, comes up short on every hip.
Gable
A gable has one ridge. Hook the tape at one end of the peak and walk it to the other end, along the top. That length is the cap order and, on a vented attic, the ridge vent order. The width of the house changes the roof area. It does not change the ridge.
Write feet and inches. A 40 ft ridge with 10% waste is 44 ft, which is 2 asphalt bundles at 25 ft each. The same ridge in the estimator: 40 × 30 ft gable at 6:12.
Hips
A hip roof adds four hips to a shorter ridge. Each hip runs from a corner of the eave up to the end of the ridge. Measure on the slope. The estimator uses (span ÷ 2) × √(2 + (pitch ÷ 12)²), where the span is the shorter side of the plan.
On a 40 by 30 ft hip at 6:12 the ridge is 10 ft and each hip is about 22.5 ft. Four hips are 90 ft. The order is the ridge plus the hips, 100 ft before waste. Open that plan: 40 × 30 ft hip at 6:12.
A steeper pitch makes the hips longer. It does not make a gable ridge longer. If the plan is square, the four hips meet at a point and the ridge length is zero. There is nothing left to put a ridge vent on.
An L, or a wing you add
Measure every ridge, then stop. The valley, the sunken line where two roofs meet, is metal flashing, not cap shingles. On a gable wing the cap run is the wing’s own ridge: how far the wing sticks out from the main roof, measured along the peak.
Draw mode in the estimator does this as a planning model. Add a wing on each side that has one, and read the total before you buy. Then confirm both ridges with the tape. A 48 × 36 ft main roof with one 18 ft wing is a starting point, not a substitute for the measurement.
What to write down
- Ridge length, in feet and inches, along the peak.
- Each hip, separately, on the slope. Do not assume all four match if a chimney or a cricket cuts one.
- Pitch, as rise per 12 inches of run. The degree reading on a phone is a check, not the order.
- The cap product on the wrapper. Asphalt bundles are often 25 linear feet, and some are 20 or 31.
Estimates are for planning purposes only. The tape is the order.