Loan Roofing Estimator
Measure the house, not the roof. Enter the footprint, pick the pitch, and this estimator climbs it for you: true roof area, squares, shingle bundles, underlayment rolls, ridge cap and nails — with the waste allowance every roofer adds before ordering.
The footprint is the building outline the roof covers. For an L-shaped house, split it into rectangles, run each one, and add the bundles. Gable overhangs add a little area — the waste allowance usually covers them.
How it works
Roof area is not the footprint — a pitched roof is the hypotenuse of the slope. The estimator multiplies the footprint by the pitch factor √(1 + (rise ÷ 12)2): 1.054 at 4/12, 1.118 at 6/12, 1.202 at 8/12. Shingles are counted in squares (100 sq ft of finished roof) at 3 bundles per square for standard architectural shingles. Underlayment rolls are counted at 400 sq ft of coverage per roll (a typical synthetic roll, applied over the bare roof area). Ridge cap comes in bundles covering about 35 linear feet each. Nails run about 320 per square — four nails per shingle, roughly 80 shingles to a square. The waste allowance (10% is standard for a simple gable, 12–15% for cut-up roofs with valleys) is applied to the shingle count, which is where cutting loss actually happens.
Formula & worked example
Formula: Roof area = footprint × pitch factor, where the factor is √(1 + (rise ÷ 12)2) — 1.054 at 4/12, 1.118 at 6/12, 1.202 at 8/12. Squares = area with waste ÷ 100; bundles = squares × 3; underlayment rolls = bare roof area ÷ 400 sq ft; ridge bundles = ridge feet ÷ 35; nails ≈ squares × 320.
Worked example: A 40 × 30 ft house (1,200 sq ft footprint) at 6/12 pitch: factor 1.118, true roof area 1,341.64 sq ft, and with 10% waste that is 14.76 squares — 45 bundles of shingles, 4 rolls of underlayment, 2 ridge-cap bundles and about 4,723 nails.
When to use this
- Re-roofing your own house and building the materials list before getting supplier quotes.
- A roofer's quote lists bundles and rolls you want to sanity-check against your own measurements.
- You're adding a roof over an addition, garage or shed and ordering materials yourself.
- Comparing shingle quotes per square — you need your true square count first, pitch included.
How to use it, step by step
- Measure the building footprint the roof covers — length × width of the outline, not the sloped surface.
- Estimate the pitch from the attic or with a level app: rise over a 12-in run.
- Enter the ridge and hip total length (the ridge beam length is a good default for a simple gable).
- Set waste: 10% simple roofs, 15% for valleys and dormers.
- Order the bundles shown, and confirm bundle coverage on the wrapper of the shingle you chose.
What the inputs mean
| Input | What it is | Typical values |
|---|---|---|
| Length & width | The building footprint the roof covers | 30–60 ft × 24–40 ft for houses |
| Pitch | Slope as rise per 12 in of run; drives the area factor | 4/12 to 8/12 on most houses |
| Ridge + hip length | Linear feet needing ridge cap shingles | Ridge length of the house, typically |
| Waste % | Cutting and damage allowance on shingles | 10% simple, 15% complex |
Another worked example
A second house: 50 × 24 ft footprint, gentler 4/12 pitch, 12% waste, 50 ft of ridge. The factor drops to 1.0541, so the true roof area is 1,264.91 sq ft — less than the steeper default despite the same footprint — giving 14.17 squares, 43 bundles, 4 underlayment rolls, 2 ridge bundles and 4,534 nails.
Frequently asked questions
How many bundles of shingles do I need for 1,200 sq ft?
It depends on pitch. A 1,200 sq ft footprint at 6/12 pitch is really 1,341.64 sq ft of roof; with a 10% waste allowance that is 14.76 squares, and at 3 bundles per square you order 45 bundles. The same footprint at 4/12 needs 43 bundles — pitch is real material.
What is a square in roofing?
A square is 100 sq ft of finished roof area — the unit shingles, underlayment and most roofing quotes are priced in. A 2,000 sq ft roof is "20 squares" no matter what the house footprint is.
How much waste should I add?
Ten percent for a simple gable or hip roof with few penetrations. Fifteen percent if the roof has valleys, dormers, skylights or many cuts — every valley eats shingles on both sides. Ordering one or two bundles extra beats a mid-job store run; most suppliers take back unopened bundles.
How many nails does a roof take?
About 320 nails per square with the standard 4-nail pattern (roughly 80 shingles per square). The default roof here — 14.76 squares — works out to 4,723 nails. High-wind zones use a 6-nail pattern, which raises the count by half.
Does the pitch factor really matter?
Yes. Moving from 4/12 to 8/12 grows the same footprint by about 14% more roof — on a 1,200 sq ft footprint that is roughly 180 extra sq ft, nearly 2 squares, or about $250–$400 of shingles and underlayment at typical prices.
💲 What will the whole job cost?
Materials are only part of a roof bill. The Roof Replacement Cost Estimator prices the full tear-off and install by material and complexity.
How many squares is a 2,000 sq ft roof?
Twenty squares by definition — a square is 100 sq ft. The catch is that a 2,000 sq ft house footprint is not a 2,000 sq ft roof: at 6/12 it is about 2,236 sq ft of roof, or 22.4 squares before waste.
Can I measure pitch from the ground?
Roughly: a pitch app on a phone sighted along the gable end works, and the attic gives an exact rise-over-run with a tape and level. One pitch step (say 6/12 vs 7/12) changes materials by about 4% — worth measuring rather than guessing.