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Roofing Calculator

By , Editor Last reviewed

Enter your house's size, overhang and roof pitch. Get the roof area, squares and shingle bundles, plus every accessory: starter, hip and ridge cap, underlayment, ice barrier, drip edge and nails. No address, email or sign-up.

Your roof

Measure the house wall to wall (outside walls). Add the overhang below. Length runs along the ridge; width is eave to eave.

Main roof
ft
ft
/ 12
Rise in inches per foot
in
Past the walls, on every edge
ft
Where two roofs meet
%
Your allowance; cut-up roofs need more
Pitch finder: rise over run
in
in

That's a – pitch (–°).

Products, ice barrier, nails and prices
sq ft
ft
ft
sq ft
Owens Corning ProArmor, with laps
ft
Lapped 2 in at joints (IRC)
Nails per shingle
$
$
$
$
$
$

You need

– bundles of shingles

– sq ft of roof · – squares · includes –% extra

  • Starter strip– bundles · – ft
  • Hip & ridge cap– bundles · – ft
  • Underlayment– rolls
  • Drip edge– pieces · – ft
  • Roofing nailsabout –
Edge lengths
  • Eaves– ft
  • Rakes (on the slope)– ft
  • Ridges– ft
  • Hips– ft

Shopping list

    Quick answer: a 40 × 30 ft house with 12 in overhangs and a 6/12 gable roof has about 1,503 sq ft of roof (15 squares). With 10% extra that's 51 bundles of GAF Timberline HDZ or Owens Corning Duration shingles, 2 bundles of ridge cap and 2 rolls of synthetic underlayment.

    How the calculator works

    Slope factor: √(1 + (pitch ÷ 12)²)
    Roof area: (length + 2 × overhang) × (width + 2 × overhang) × slope factor
    Bundles: roof area × (1 + waste%) ÷ coverage per bundle
    Hip length: half the short side × √(2 + (pitch ÷ 12)²), four hips
    Drip edge: (eaves + rakes) ÷ (piece length − 2 in lap)

    For planes that share one pitch, the roof's area is its footprint times the slope factor, whatever the shape. That's why a hip roof and a gable roof over the same house need the same shingles; the shape changes only the edges. Pitches differ between sections? Enter each section separately.

    Pitch multipliers

    PitchAngleSlope factorRoof area per 1,000 sq ft of footprint
    3/1214°1.0311,031 sq ft
    4/1218.4°1.0541,054 sq ft
    5/1222.6°1.0831,083 sq ft
    6/1226.6°1.1181,118 sq ft
    7/1230.3°1.1581,158 sq ft
    8/1233.7°1.2021,202 sq ft
    9/1236.9°1.2501,250 sq ft
    10/1239.8°1.3021,302 sq ft
    12/1245°1.4141,414 sq ft

    The factors match the tables in IKO's estimating guide.

    Roofing materials compared

    Minimum slopes are from the 2021 International Residential Code; your local code may differ. Weights come from the sources listed and vary by product. Service lives are HUD's 2015 ranges, based on 2007 builder data, and HUD itself cautions that such estimates “must be taken with a grain of salt.” A warranty term isn't a lifespan.

    MaterialLowest pitch (IRC)WeightService life (HUD)Good to know
    Asphalt shingles2:12 (R905.2.2); double underlayment from 2:12 up to 4:122.4 to 3.2 lb per sq ft for one layer (a metal-roofing maker’s figure)15–30 years (“composition shingle”)The most common US roof. Look for Class A fire rating and, in hail country, a UL 2218 Class 4 impact rating.
    Metal panels, standing seam¼:12 for standing seam; lapped seams 3:12 without sealant, ½:12 with (R905.10.2)0.8 to 1.5 lb per sq ft (a metal-panel maker’s figure)20–50+ years (standing seam)Light and suited to low slopes. Cool-roof versions reflect more sunlight (check the Cool Roof Rating Council directory).
    Metal shingles3:12 (R905.4.2)——Metal formed to look like shingles, slate or shakes. We found no authoritative weight or life figure.
    Concrete tile2½:12; double underlayment from 2½:12 up to 4:12 (R905.3.2)About 720–970 lb per 100 sq ft (one maker’s profile)50+ years (“concrete/clay tile”)Heavy: switching to tile from shingles can need a check of the roof framing by an engineer or your building department.
    Clay tile2½:12; double underlayment from 2½:12 up to 4:12 (R905.3.2)About 750 lb per square for one profile; others are heavier50+ years (“concrete/clay tile”)Heavy, like concrete tile. Weight varies a lot by profile, so use the product’s own figure.
    Slate4:12 (R905.6.2)500 to 1,400 lb per square, by thickness and size50–100 yearsThe heaviest common roof. Needs framing designed for the load and an experienced slate installer.
    Wood shakes and shingles3:12 (R905.7.2 shingles, R905.8.2 shakes)—15–30 years (“wood shingle”)Check fire-rating rules first: some areas require Class A roofs.

    Before anyone goes up

    OSHA calls falls the leading cause of death in construction: 389 of 1,034 construction deaths in 2024 were falls to a lower level. Measure from the ground, the attic and the plans where you can, and weigh the job with the DIY vs hire a pro calculator. Hiring? Compare roofers with the contractor checklist, schedule the job in the timeline planner, and look up terms like square, rake and pitch in the glossary. Need the footprint of an L-shaped house? Use the square footage calculator.

    Common questions

    How many bundles of shingles do I need?

    Divide the roof area plus waste by the coverage per bundle. For GAF Timberline HDZ and Owens Corning Duration, three bundles cover 98.4 sq ft, a little less than a 100 sq ft “square”, so a 40 × 30 ft house with 12 in overhangs and a 6/12 gable roof (1,503 sq ft) needs 51 bundles with 10% extra. Counting a flat 3 bundles per 100 sq ft would leave you short.

    What is a roofing square?

    A 10 × 10 ft area: 100 sq ft of roof. Roof prices and shingle coverage are usually quoted per square.

    How do I find my roof pitch?

    Pitch is inches of rise per 12 in of level run. From the attic or a ladder at the gable end, hold a level against the rafter or roof, measure 12 in along it, and measure straight up to the roof. Our pitch finder converts any rise and run. Don’t climb onto a roof to measure it.

    Does a hip roof need more shingles than a gable roof?

    Not for the same pitch and overhangs: both cover the same area, because roof area is the footprint times the slope factor. A hip roof has more edges and hips, though, so it needs more ridge cap and starter, and usually more waste from cutting along the hips.

    Do I need an ice barrier?

    Where your jurisdiction says ice dams are a local problem. The 2021 IRC requires one for shingle roofs where Table R301.2 is marked “YES”, reaching at least 24 in inside the exterior wall line (and at least 36 in up the slope on 8:12 and steeper roofs). Your building department can tell you.

    Can I put asphalt shingles on a low-slope roof?

    Only down to 2:12. Between 2:12 and 4:12 the IRC requires a double layer of underlayment, which this calculator adds automatically. Below 2:12, use a covering rated for low slopes, such as standing-seam metal.

    Sources

    Formulas and figures last checked against these sources on. Spotted an error? Tell us and we'll fix it.

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