Roofing Materials Calculator

Estimate total roof square footage, roofing squares, shingle bundles, underlayment rolls, ridge cap, and nails for any pitch. Adjust the waste factor to match cut-up roofs or simple gables. Built for roofers, GCs, and homeowners planning a re-roof.

How This Calculator Works

Roofers measure in “squares,” where one square equals 100 square feet of roof surface. The calculator finds the footprint — length × width × the number of roof sections — then multiplies by a pitch factor to convert that flat footprint into actual sloped area, since a steep roof has more surface than the ground it covers. A waste factor is added for cuts, hips, and valleys, and the total is divided by 100 to get squares.

From squares it derives the order: shingle bundles at 3 per square (standard 3-tab and architectural coverage), underlayment rolls at one per 400 sq ft, ridge-cap bundles at roughly 35 linear feet of ridge per bundle, and nails at about 2 lbs per square. That mirrors how a supplier loads a roofing job — squares first, then everything else scales off it.

A Worked Example

A simple gable roof, two sections each 40 ft by 18 ft, on a 6/12 pitch (factor about 1.118), 10% waste, with 40 ft of ridge. Footprint: 40 × 18 × 2 = 1,440 sq ft. Pitched: 1,440 × 1.118 = 1,610 sq ft. Add 10% waste = 1,771 sq ft, which is 17.71 squares. Bundles: ceil(17.71 × 3) = 54. Underlayment: ceil(1,771 ÷ 400) = 5 rolls. Ridge cap: ceil(40 ÷ 35) = 2 bundles. Nails: about 35.4 lbs.

Estimator's tip: Always order a full extra bundle or two beyond the count, and keep them banded and dry for the inevitable repair — matching a discontinued shingle three years later is a nightmare. On anything past a simple gable, walk the roof and add your hips and valleys to the waste; every cut shingle in a valley is a partial you throw away, which is why complex roofs blow past the default 10% fast.

What Affects Your Shingle Order

• Roof pitch — the steeper the slope, the larger the multiplier on your flat footprint.
• Number of facets, hips, and valleys, which raise waste from the typical 10% toward 15%+.
• Shingle type: architectural, 3-tab, and designer shingles vary in bundles per square.
• Ridge and hip length, which drives separate cap-shingle bundles.
• Tear-off versus overlay, affecting underlayment and starter needs.
• Penetrations like skylights and chimneys that you flash and work around.
• Starter strip and drip edge along eaves and rakes, ordered by linear foot separately from field shingles.
• Climate and exposure — high-wind and coastal jobs may call for extra nails per shingle, raising fastener weight.

Frequently Asked Questions

How many bundles of shingles per square?

Three bundles cover one roofing square (100 square feet) for standard 3-tab and most architectural shingles. Heavier designer shingles can take four bundles per square, so check the wrapper.

What is a roofing square?

A roofing square is 100 square feet of roof surface, measured along the slope, not the ground. Roofers order shingles, underlayment, and labor by the square rather than by square foot.

How do I account for roof pitch?

Multiply your flat footprint by a pitch factor: about 1.03 for a 3/12, 1.118 for a 6/12, and 1.25 for a 9/12. The calculator applies the factor you choose so the squares reflect true sloped area.

How much waste should I add for roofing?

Ten percent suits a simple gable roof. Complex roofs with many hips, valleys, and dormers waste more on cuts, so 15% is safer. Steep-slope starter and ridge work also add to the order.