Shingle Coverage Chart & Calculator

The model, stated exactly

Roofing squares = roof area in square feet ÷ 100, rounded up to whole squares. Bundles before waste = squares × 3, on the single stated basis of architectural shingles at 3 bundles per square. Bundles to buy = bundles before waste × (1 + waste percentage ÷ 100), rounded up to whole bundles. The rounding matters: you cannot buy 59.4 bundles, so the order is always the next whole bundle up. The basis is fixed for the whole page — if your shingles are 3-tab at 3 bundles per square the same arithmetic holds, but if your product bundles cover a different area, check the bundle coverage printed on the wrapper and adjust.

The worked example, line by line

Setup: 1,800 sq ft, 10% waste, 3 bundles per square.

Line 1 — squares. 1,800 ÷ 100 = 18 squares.

Line 2 — bundles before waste. 18 × 3 = 54 bundles.

Line 3 — add waste. 54 × 1.10 = 59.4 bundles.

Line 4 — round up. 59.4 rounds up to 60 bundles to buy.

Try these

1,200 sq ft at 10% waste. 12 squares, 36 bundles before waste, 39.6 with waste — buy 40 bundles.

2,400 sq ft at 10% waste. 24 squares, 72 bundles before waste, 79.2 with waste — buy 80 bundles.

1,800 sq ft at 0% waste. 18 squares, 54 bundles, no waste added — buy 54 bundles. Useful only as a check figure; never order a real roof with zero waste.

1,800 sq ft at 15% waste. 18 squares, 54 bundles before waste, 62.1 with waste — buy 63 bundles. Complex roofs with many valleys earn the higher allowance.

Reference table: bundles to buy at 10% waste

Print this table before you call the supplier: every row already includes the 10% waste and the round-up, so the last column is the order quantity for a straightforward roof.

Output · formula · meaning

Who uses this

• The homeowner checking a roofer's quote: enters 1,800 sq ft and 10% waste and confirms 60 bundles — if the quote says 80, something needs explaining before signing.
• The DIYer re-roofing a garage: enters 1,200 sq ft and reads 40 bundles off the table, then orders once instead of making a second trip mid-job.
• The buyer comparing supplier prices: enters the roof area once and uses the bundle count to compare per-bundle prices fairly, instead of comparing total quotes that hide different waste allowances.
• The owner of a cut-up roof: enters 15% waste and sees 63 bundles for 1,800 sq ft — the extra 3 bundles are the price of valleys and dormers, planned before the crew arrives.

Accuracy & limitations

The arithmetic is exact on its stated basis, but three inputs deserve care. First, roof area means roof surface area, including slope — a pitched roof is larger than the house's footprint, and using floor area undercounts by the slope factor. Second, the 3-bundles-per-square basis is architectural shingles; always check the coverage printed on your product's wrapper, because some products bundle differently. Third, waste is a judgment call: 10% suits a straightforward gable roof, while hips, valleys, dormers, and steep pitches push it toward 15% or more. The calculator also does not count ridge caps, starter strips, underlayment, or flashing — those are separate line items on any real order. Error policy: missing, non-numeric, or non-positive roof area and a negative waste percentage are reported as errors rather than calculated, so no result ever shows NaN.