Roofing Calculator
Squares, shingle bundles, underlayment and nails — from the footprint you can actually measure, with the pitch multiplier done for you.
The footprint of the building, including eave overhang — not the roof surface. The pitch below converts one to the other.
Rise in inches per 12 inches of horizontal run. Measure it with a level and a tape in the attic if you can't get on the roof.
The actual sloped surface, all planes added together — not the footprint.
If a roofer quoted you in squares, enter that number. One square = 100 sq ft.
Check the wrapper before you order. Assuming 3 when the shingle packs 4 is the most common way a roofing order comes up a pallet short.
Add every ridge and hip. Cap bundles cover about 20 linear ft each.
For starter strip along the bottom edge — about 105 ft per bundle.
You need
Enter dimensions
| Also on the order | Amount |
|---|---|
| Pitch multiplier | — |
| Underlayment | — |
| Roofing nails (1¼″) | — |
| Hip & ridge cap | — |
| Starter strip | — |
Architectural bundles commonly run $33–$45.
What Will This Roof Cost to Replace?
Roofing is priced by the square — 100 square feet of roof surface — which is exactly what the calculator above gives you. Pick your material and whether the old roof comes off, and this prices the replacement.
Most codes allow only two layers total, and a second layer hides deck rot you'd otherwise catch. Insurers and manufacturers generally prefer a full tear-off.
Estimated replacement cost
Enter roof dimensions above
| Line item | Amount |
|---|---|
| Installed price | — |
| Tear-off & disposal | — |
| Labor portion | — |
National ranges for planning and sanity-checking a bid — not a quote. Steep pitches, multiple stories, valleys, and skylights all add cost.
What roofing costs per square in 2026
| Material | Installed per square | Typical 20-square roof | Expected life |
|---|---|---|---|
| 3-tab asphalt | $350–550 | $7,000–11,000 | 15–20 years |
| Architectural shingles | $450–750 | $9,000–15,000 | 25–30 years |
| Corrugated metal | $900–1,600 | $18,000–32,000 | 40–50 years |
| Standing-seam metal | $1,100–2,000 | $22,000–40,000 | 50+ years |
Tear-off and disposal add $100–200 per square. A "square" is 100 sq ft of roof surface, not floor area.
Reading a roofing bid without getting taken
Labor is about 60% of a shingle roof. Materials are the visible part of a quote, but the crew is what you're really buying — and it's where bids diverge.
- Check the square count first. Divide the bid by the squares in your estimate above. If a contractor's square count is far off yours, ask why before discussing price — pitch and waste assumptions are the usual reason.
- Deck repair is almost always excluded. Bids say "additional plywood at $X per sheet" because nobody knows what's under the shingles until they're off. Budget a contingency of a few sheets.
- Pitch changes the price. Anything above 6/12 needs staging and fall protection; 9/12 and up can add 25–50% to labor on the same square footage.
- Ask what underlayment and ice-and-water shield are included. Synthetic underlayment and proper ice barrier at the eaves cost more than felt and are worth it in freeze-thaw climates.
- Layering over saves money now and costs later. It skips tear-off, but the second layer can't be inspected, traps heat, and makes the eventual removal twice the job.
- Metal costs 2–3× asphalt up front and lasts two to three times as long. Over 50 years the math often favors metal — over a 7-year stay in the house, it rarely does.
How to Calculate Roofing Materials
A roof is bigger than the house under it, and the pitch is what decides by how much. Every estimate is the same four steps:
- Footprint area: length × width, including the eave overhang.
- Pitch multiplier: √(rise² + 144) ÷ 12. This is the slope length of a rise-in-12 triangle — a 6/12 roof is 1.118× its footprint.
- Squares: roof area ÷ 100, plus 10–20% waste.
- Bundles: squares × bundles per square, rounded up.
Roofing formulas
Roof area = footprint × √(rise² + 144) ÷ 12
Bundles = (roof area × 1.10 ÷ 100) × bundles per square, rounded up
Worked example — 40 × 30 ft house, 6/12 pitch: footprint 1,200 sq ft × 1.118 = 1,342 sq ft of roof. Add 10% waste → 1,476 sq ft = 14.8 squares. At 3 bundles per square that's 45 bundles, 2 rolls of synthetic underlayment and about 34 lb of nails.
Pitch Multipliers
Multiply your footprint by this to get roof surface:
| Pitch | Multiplier | Angle | 1,200 sq ft footprint becomes |
|---|---|---|---|
| 3/12 | 1.031 | 14° | 1,237 sq ft |
| 4/12 | 1.054 | 18° | 1,265 sq ft |
| 6/12 | 1.118 | 27° | 1,342 sq ft |
| 8/12 | 1.202 | 34° | 1,442 sq ft |
| 10/12 | 1.302 | 40° | 1,562 sq ft |
| 12/12 | 1.414 | 45° | 1,697 sq ft |
The Bundles-Per-Square Trap
Almost every guide online tells you three bundles make a square and stops there. That's true for three-tab and for most standard architectural shingles — and wrong often enough to cost you a second trip.
- 3 bundles/square — three-tab and standard architectural. Roughly 26–29 shingles per bundle for three-tab, 22–25 for architectural.
- 4 bundles/square — heavyweight architectural and several designer lines.
- 5 bundles/square — premium designer, slate-look and shake-look profiles.
- Read the wrapper. Coverage per bundle is printed on it. That number, not a rule of thumb, is what your order should be built on.
Before You Order
- Measure the footprint, not the roof. Getting on a steep roof with a tape is the dangerous way to get a number you can calculate from the ground.
- Valleys and hips eat shingles. Every one means angled cuts and discarded offcuts — that's what the 15% waste tier is for.
- Ice-and-water shield is usually code at the eaves in freeze-thaw climates, and it's separate from your field underlayment. Check locally.
- High-wind zones want six nails per shingle, not four — that's 480 per square instead of 320, and it's often a warranty condition.
- Order the ridge cap as cap, not by cutting up field shingles, if the manufacturer's warranty calls for matching cap.
Frequently Asked Questions
How many bundles are in a square?
Three for three-tab and most architectural — but 4 or 5 for heavyweight and designer lines. Check the wrapper; assuming 3 is the most common way an order comes up short.
How do I get roof area from my footprint?
Multiply by the pitch multiplier, √(rise² + 144) ÷ 12. A 6/12 roof is 1.118× the footprint; 12/12 is 1.414×.
What is a roofing square?
100 sq ft of roof surface. Roofing is quoted and sold by the square, which is why every estimate converts to it.
How much waste should I add?
10% on a simple gable, 15% with valleys, hips or dormers, 20% on a cut-up roof or where the pattern must align.
How many nails per square?
About 320 at four per shingle; 480 in high-wind zones at six per shingle. Roughly 140 nails to the pound.
How much underlayment?
Synthetic rolls cover 10 squares, #15 felt 4 squares, #30 felt 2. Ice-and-water shield at the eaves is extra and often required by code.
My roof has more than one pitch — how do I measure it?
Calculate each section separately with its own pitch multiplier, then add the areas together before converting to squares. Treating a multi-pitch roof as one average pitch is how orders come up short on the steepest sections.
How many ridge cap bundles do I need?
Measure total ridge + hip length in feet, then divide by about 35 linear ft per bundle — check the wrapper, since it varies by brand. This is separate from the field bundles this calculator returns above.
Does waste percentage change by roof shape, not just size?
Yes — 10% covers a simple gable, 15% once hips, valleys or dormers show up, and up to 20% on a cut-up roof or a pattern that has to align. Set the waste input above to match your roof's complexity rather than adding "a little extra" on top of the total separately.
How much does it cost to replace a roof?
Most asphalt replacements run $9,000–18,000. Per square: $350–550 3-tab, $450–750 architectural, $1,100–2,000 standing-seam metal.
How much does tear-off add?
$100–200 per square — $2,000–4,000 on a typical 20-square roof. Layering over skips it, but hides deck rot and most codes cap you at two layers.
Is a metal roof worth the extra cost?
It's 2–3× the price and lasts 40–50+ years vs 25–30 for architectural shingles. Good value if you're staying put; rarely pays back on a short stay.
References
- Asphalt Roofing Manufacturers Association — residential asphalt shingle guidance: asphaltroofing.org
- NRCA — The NRCA Roofing Manual (steep-slope assemblies): nrca.net
- International Residential Code, Chapter 9 — roof assemblies, underlayment and fastening: codes.iccsafe.org
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