How to Calculate Roofing Materials

Fencing is pretty straight forward and we work on the ground and in straight lines, roofing on the other hand is up in the air, on a slope and a few other exciting things.  We work with Roofing and other General Contractors, so I thought this info I was given might be helpful so here it is…

The first thing to know is that if you order shingles based solely on the Squares or Square foot area of the roof, you won’t have enough. You will need shingles for starter courses along the eaves and at some rakes, and you will need shingles to cap hips and ridges.   You can cut shingles to use as these caps, ridges and starter, as well as cutting at the rakes, against walls and chimneys, and at valleys.  This cutting will always cause some waste.  Some of the cutoffs will be big enough to use as starter shingles or in other areas where cut shingles are needed, but smaller cutoffs will be waste.  Waste can vary from 1-5% depending on the complexity of the roof.

    The only roof that will generate no waste from cutting is a simple gable roof whose length is divisible by the 3-ft. length of a shingle.

Starter Shingle – is the shingle at the ‘bottom edge’ of the roof with the exposure portion trimmed off, leaving just the self-seal strip and top lap. They are fastened along the eaves edges to seal down the first course of shingles and provide coverage material beneath the tab cutouts just like the top lap of each successive course.

Starter Shingle Example

Starter Shingle Diagram

You calculate starter from the parameter measurement, the same as the Drip Edge generally

    Parameter Linear Feet/120 = # of Bundles of Starter for 20 yearParameter Linear Feet/80= # of Bundles of Starter for 30 year

Ridgethere are various types, like rapid ridge which provides stronger ridges that are further resistant to damage, stand slightly higher and look nice on your roof cap lines.  However in most cases regular shingles are cut to be used as ridge.

  • Rapid Ridge is usually 20LF per box
  • Standard Ridge (cut shingles) can cap 35 lin. ft. of ridges and hips with each bundle of shingles.

    Calculating Ridge

  • Hip + Ridge = Ridge Needed
  • Linear Feet/33 = # of bundles needed for ridge
  • *Ridge Vent use 9in for 30 year shingles

Drip Edge

    Linear feet/10 + 5 = Drip Edge Needed (1 1/2 x 1 1/2)


    Linear feet/33 = # of rolls needed


    Number of Squares/4 = # of rolls of 15# felt needed
    Number of Squares/2 = # of rolls of 30# felt needed


    1 box per 20-25 squares

Flashing? – 1 roll per job?