Hip and ridge cap is a separate product from field shingles, and a bundle of it covers roughly 20 to 25 linear feet. Measure every ridge and every hip and add them together.
Cap is not field shingle
Purpose-made cap shingles are thicker and pre-scored to bend over the ridge without cracking. Cutting field shingles into caps works on three-tab but not on architectural shingles, which are too thick to fold.
Matching cap is sold under the same product line as the field shingle, so order it at the same time from the same lot.
Ridges and hips both count
A simple gable roof has one ridge. A hip roof has a short ridge plus four hips running down to the corners, which usually adds up to considerably more cap than the ridge alone.
Walk the roof outline on a plan or a satellite image and add every line where two planes meet at the top.
Direction matters
Cap is laid starting at the end away from the prevailing wind, working towards it, so the exposed edge never faces into the weather.
On a hip, cap starts at the bottom and works up so each piece laps over the one below it.
Ventilated ridge changes the material list
If the roof has a ridge vent, the cap shingles go over the vent rather than directly on the deck, and the vent itself is a separate linear-foot item.
Ridge vent comes in rolls or rigid sections and the deck has to be cut open along the ridge for it to do anything — typically an inch or so either side of the peak, stopping short of the ends.
The nails also have to be longer, because they now pass through the cap, the vent, and into the deck. Standard ridge cap nails are too short for a vented ridge and will not hold.
Starting and finishing a run
Cap shingles are laid starting from the end of the ridge that faces away from the prevailing wind, so the exposed edge of each cap points downwind rather than into it.
On a hip, caps run from the bottom upward. Where several hips meet a ridge at the peak, the last few pieces are cut and blended, and that junction takes a couple of extra caps beyond the linear arithmetic.
The final cap on any run is fastened with exposed nails, which have to be sealed. That dab of roofing cement is the most commonly skipped step on a roof and a routine source of a slow leak at the peak.