Roofing Shingle Calculator
Calculates the number of roofing squares needed to cover a roof, including a user-defined waste allowance. Use this when ordering shingles for a new roof or a re-roofing project.
About this calculator
In roofing, one square equals 100 square feet of coverage. To find the number of squares required, divide the total roof area by 100. However, shingles are always wasted due to cuts at ridges, hips, valleys, and edges, so a waste percentage is added before dividing. The formula is: Squares = (roofArea × (1 + wastePercentage / 100)) / 100. Typical waste allowances range from 10% for a simple gable roof to 15–20% for complex hip or valley roofs. Most shingle bundles cover one-third of a square (about 33 sq ft), so multiply your squares result by 3 to get the number of bundles to purchase.
How to use
Suppose your roof area measures 1,800 sq ft and you want a 15% waste allowance. Step 1 — Apply the waste factor: 1,800 × (1 + 15/100) = 1,800 × 1.15 = 2,070 sq ft. Step 2 — Divide by 100 to convert to squares: 2,070 / 100 = 20.7 squares. Step 3 — Round up to the nearest whole square: 21 squares. Step 4 — Multiply by 3 for bundles: 21 × 3 = 63 bundles of standard three-tab shingles.
Frequently asked questions
How do I calculate the number of roofing squares for a gable roof?
Measure the length and width of each roof plane and multiply to get the area of that plane. Sum all planes to get the total roof area in square feet, then divide by 100 to get squares. Add a 10% waste allowance for a simple gable roof by multiplying by 1.10 before dividing. Always measure the actual sloped surface, not the horizontal footprint, to account for roof pitch.
What waste percentage should I use when ordering roofing shingles?
A 10% waste factor is standard for straightforward gable roofs with few penetrations. Roofs with hips, valleys, skylights, chimneys, or dormers typically require 15–20% waste. Steeper pitches also generate more waste because cuts are more frequent and less material is reusable. When in doubt, rounding up to the next full square is a low-cost insurance policy against running short.
How many shingle bundles are in a roofing square?
Standard three-tab asphalt shingles come 3 bundles per square, with each bundle covering approximately 33 square feet. Architectural (dimensional) shingles can require 3 or 4 bundles per square depending on the manufacturer, so always check the product label. To convert your calculated squares to bundles, multiply by the bundle-per-square count listed on the packaging.