Roofing materials calculator for a shingle roof

A shingle roof take-off has two halves. The field of the roof, the shingles and the underlayment, is counted from the area. Everything at the edges and the peaks, the starter, ridge cap, drip edge and most of the leak barrier, is counted from the lengths.

1. Footprint. The area the roof covers seen from above, overhangs included. Measure it on the ground and add the overhangs, take it from the plans, or trace it on a satellite image.
2. Pitch factor. A sloped roof has more area than its footprint. The factor is √(1 + (rise ÷ 12)²): 1.118 for a 6/12 roof, 1.414 for 12/12.
3. Roof area = footprint × pitch factor. Divide by 100 for squares.
4. Waste. Add an allowance for cuts at hips, valleys, rakes and dormers. Use what your own jobs run; complex roofs run higher.
5. Edges. Measure the eaves (the level bottom edges), the rakes (the sloped gable edges, measured along the slope), the ridges, the hips and the valleys.

The calculator does the rest with the product figures below. To price the whole job with labor and tear-off, use the roof replacement cost calculator; this tool is the detailed materials list behind it.

The factor works for any roof shape, hips and valleys included, as long as all the planes share one pitch. For a roof with mixed pitches, run each section on its own and add them. GAF shingles must be installed on slopes of 2/12 or steeper, and between 2/12 and 4/12 its instructions call for two layers of underlayment over the whole deck. The calculator flags that, so you can double the underlayment rolls.

Every figure below is from the manufacturer's data sheet or installation instructions, or from the building code. The calculator uses GAF's products as the reference because their sheets are public and widely stocked; other brands are close but check the wrapper.

Roll coverages are nominal and do not include laps, so the calculator applies your waste allowance to the rolls as well as to the shingles.

• Starter strip goes along the eaves under the first course, so the shingle edges are sealed down and the joints in the first course are covered. GAF recommends it at the rakes too, and requires it there for its enhanced wind warranty, so the calculator counts both unless you turn the rakes off.
• Ridge cap covers the ridges and the hips. Hips are easy to forget on a hip roof, where they can add more length than the ridge itself.
• Drip edge is required by IRC R905.2.8.5 at the eaves and rakes of shingle roofs, with adjacent pieces lapped at least 2 in. A 10 ft piece therefore covers 9 ft 10 in, which is why 100 ft of edge takes 11 pieces, not 10.
• Leak barrier (ice and water shield) goes along the eaves where ice dams happen. GAF's instructions run it from the eave to at least 24 in past the inside of the exterior wall. One 36 in row does that on a narrow overhang and a moderate pitch; wide overhangs or a low pitch can need two rows. It also lines the valleys, where water from two planes meets.

The underlayment is counted on the deck that is left after the leak barrier, since the two do not need to overlap except at their laps.

A 2,400 sq ft footprint, 8/12 pitch, 15% waste for the hips and a valley. 200 ft of eaves, no rakes, 20 ft of ridge, 110 ft of hips, 30 ft of valley. Two rows of leak barrier at the eaves for a cold climate, the 6-nail pattern for wind.

• Pitch factor √(1 + (8 ÷ 12)²) = 1.202. Roof area 2,400 × 1.202 = 2,884 sq ft, 28.84 squares.
• Shingles: 28.84 × 1.15 = 33.17 squares × 3 = 99.5, so 100 bundles.
• Nails: 33.17 squares × 64 shingles × 6 = 12,738 nails.
• Starter: 200 ft ÷ 120.33 = 1.66, so 2 bundles.
• Ridge cap: (20 + 110) ft ÷ 25 = 5.2, so 6 bundles.
• Drip edge: 200 ft ÷ 9.83 ft = 20.3, so 21 pieces.
• Leak barrier: 2 rows × 200 ft × 3 ft + 30 ft × 3 ft = 1,290 sq ft × 1.15 ÷ 200 = 7.4, so 8 rolls.
• Underlayment: 2,884 − 1,290 = 1,594 sq ft × 1.15 ÷ 1,000 = 1.83, so 2 rolls of synthetic.

On the simple 1,700 sq ft gable at 6/12 the calculator opens with, the list is 63 bundles, 2 starter bundles, 2 ridge cap bundles, 18 drip edge pieces, 2 leak barrier rolls and 2 underlayment rolls.

The edge lengths drive four of the seven materials, so it is worth getting them right:

• Eaves are level, so measure them on the ground along the drip line, or from the plans.
• Rakes, hips and valleys are sloped. Measure them on the roof, or work them out: a rake is the level run times the pitch factor, so a 16 ft run at 6/12 is 16 × 1.118 = 17.9 ft. A hip or valley on a roof where both planes share the pitch is longer still, because it runs on a diagonal.
• Ridges are level and are measured end to end.

A satellite measurement gives the footprint and the plan lengths in one go. The roof measurement tool traces the roof from above; enter its footprint here with the pitch you see on site.

The take-off covers the main materials. Also check the job for:

• Flashing: step flashing at walls (GAF's instructions call for 2 nails a step flashing), counter flashing, chimney and skylight kits, and pipe boots.
• Ventilation: ridge vent in place of some ridge cap, box vents, and intake at the soffits.
• Deck repair: sheets of plywood or OSB for rotten decking found at tear-off. GAF calls for at least 3/8 in plywood or OSB under its shingles.
• Fasteners for the rest: cap nails or cap staples for the synthetic underlayment, and longer nails for ridge cap.
• Local code: wind zones, ice barrier rules and the number of layers allowed vary by jurisdiction. The code as adopted where you work and the shingle maker's instructions govern.

"Save as an estimate in Koira" carries each material as its own line into an estimate, where you add your supplier's prices, the labor and the tear-off. Measure the roof from above with the roof measurement tool.