RoofingCalculator.ioHow the Roof Calculator Works
The calculator turns a roof's length, width and pitch (or just an address) into roof squares, a material list and a 2026 installed cost range. The math is exact for simple roofs. Prices start from national averages, and a ZIP code tunes the labor to your state.
How is roof area calculated?
Roof area is the flat footprint (length times width, plus any overhang) multiplied by a pitch factor. The factor is the square root of 1 plus (rise ÷ 12) squared, which is how much longer a sloped rafter is than the flat run under it.
On a 50 by 30 foot house with a 6/12 roof, the footprint is 1,500 square feet. Multiplied by 1.118, that's 1,677 square feet of actual roof, or 16.8 squares (a square is 100 square feet).
- Pitches from 0/12 to 24/12
- Overhang up to 4 ft per side
- Exact for simple gable and hip roofs
| Pitch | Multiplier | Extra roof area |
|---|---|---|
| 0/12 | 1.000 | +0.0% |
| 3/12 | 1.031 | +3.1% |
| 4/12 | 1.054 | +5.4% |
| 6/12 | 1.118 | +11.8% |
| 8/12 | 1.202 | +20.2% |
| 10/12 | 1.302 | +30.2% |
| 12/12 | 1.414 | +41.4% |
The takeoff turns roof area into order quantities
The takeoff turns roof area into order quantities. Shingles are ordered at 3 bundles per square. Synthetic underlayment covers about 10 squares a roll and No. 15 felt about 4, and both double up on 2/12 to 4/12 slopes, where code requires two layers under shingles and tile.
Edge materials come from the roof's geometry. Ridge cap covers the ridge plus any hips at about 25 linear feet a bundle (GAF Seal-A-Ridge; some caps run 20 or 33, so check the wrapper), starter strip runs the eaves, and drip edge runs the eaves and rakes. For the 50 by 30 example, that's 56 bundles, 2 synthetic rolls, 2 ridge cap bundles, 100 feet of starter and about 167 feet of drip edge.
- Bundles, rolls and ridge cap
- Starter strip and drip edge
- Flat membranes skip shingle accessories
Waste is added to the order, not the roof
Waste is extra material for cut-offs, and the calculator adds it to the order, not to the roof. It defaults to 10 percent for a gable roof and switches to 15 percent when you pick a hip roof, because every hip line means angled cuts on both sides.
Waste only touches materials. Labor and tear-off are priced on the roof's actual squares, since nobody installs the scraps. You can set anything from 0 to 40 percent. You don't need to pad it for valleys and dormers. Enter them and the calculator adds their cut waste on its own (about 2 square feet per foot of valley, 25 per dormer).
- 10% gable, 15% hip by default
- Adjustable from 0 to 40%
- Applied to materials only
Costs start from 2026 national averages
Every cost range starts from a 2026 US national average, split into material and labor for each roofing type. Material is priced on the waste-adjusted squares and labor on the actual squares, then the two are added together.
Tear-off adds $100 to $150 a square for each old layer removed. Labor goes up 15% for moderate jobs and 30% for difficult ones, Roofs of 8/12 and steeper are bumped to at least moderate, and 12/12 and up to difficult, because the crew needs harnesses and staging. The 50 by 30 example in architectural shingles, with one layer torn off, comes to about $9,600 to $15,600. Permits, rotted decking and local price swings aren't included.
- Material and labor priced separately
- Tear-off by layer
- Labor difficulty adjustment
| Material | Installed, per square |
|---|---|
| 3-Tab Asphalt Shingles | $380 to $550 |
| Architectural Shingles | $450 to $750 |
| Standing Seam Metal | $1,000 to $1,600 |
| Corrugated Metal | $600 to $1,000 |
| TPO / Single-Ply (Flat) | $650 to $1,100 |
| Modified Bitumen (Flat) | $550 to $900 |
| EPDM Rubber (Flat) | $400 to $1,050 |
| Concrete Tile | $900 to $1,600 |
| Clay Tile | $1,000 to $2,500 |
| Natural Slate | $1,500 to $3,500 |
| Synthetic Slate | $900 to $1,800 |
| Wood Shake | $900 to $1,400 |
Address lookup reads the footprint from OpenStreetMap
Address lookup finds the building's outline on OpenStreetMap and fills in its length and width for you. It geocodes the address, pulls the building footprints around that point, and picks the one the address falls inside (or the nearest one within about 30 meters). The outline is then boxed into a rectangle with the same area.
The lookup has limits. OpenStreetMap traces walls, not eaves, so add your overhang. It can't see pitch, so you enter that yourself. Some newer or rural buildings aren't mapped at all. When nothing matches, the calculator falls back to the largest building nearby and marks the result as approximate. Check the numbers against a tape measure or a satellite photo before ordering.
- Free OpenStreetMap data, no account
- Footprint, not roof surface
- Flags approximate matches
Hip roofs change the edges, not the area
Picking gable or hip changes the edge materials, while the area stays the same. A section is one rectangle of roof, and you can add up to 50 identical ones, such as matching wings or a row of units. Each is calculated the same way and added together.
A gable has a ridge the full length of the house and rakes at each end. A hip has a shorter ridge (length minus width), four hips running down to the corners, and eaves all the way around, which changes the ridge cap, starter strip and drip edge counts.
- Up to 50 sections
- Gable or hip geometry
- Ridge and hip lengths shown
The calculator won't price a roof below code minimum slope
The calculator checks each material against its minimum slope in the International Residential Code (section R905) and won't price a roof below it. Asphalt shingles need at least 2/12, concrete and clay tile 2.5/12, wood shakes 3/12, and natural or synthetic slate 4/12. EPDM works the other way. It's priced only up to 3/12, since it's a flat-roof membrane.
It also warns when a choice is unusual, such as shingles and tile between 2/12 and 4/12 (double underlayment), lapped corrugated metal below 3/12, and TPO or modified bitumen at 4/12 and steeper, where shingles or metal are the norm.
- IRC R905 minimum slopes
- Double underlayment below 4/12
- Low-slope and steep-slope warnings
The calculator is a ballpark, not a bid
The calculator is a ballpark for planning and qualifying a job, not a bid. The area math is exact for a rectangle with a straight gable or hip roof, so the quantities are as good as the measurements you enter.
Real roofs are more complicated. If yours has valleys, dormers, skylights or a chimney, enter them and each one shows up as its own line (valley lining, extra cut waste, dormer labor, reflashing), plus a complexity rating so you know how cut-up the job is. Labor starts at the 2026 national average. Add a ZIP code and it's scaled by your state's roofer wages from the Bureau of Labor Statistics. It can't see hidden deck damage, which only shows up at tear-off. Roofers, estimators and homeowners use it to check a quote. For a final price, get three written estimates from local contractors.
- Exact on simple roof shapes
- Valleys, dormers, skylights and chimneys priced
- Optional ZIP labor adjustment
Roof calculator questions
How accurate is the roofing calculator?
The area and material math is exact on a simple gable or hip roof, for the measurements you enter. Costs start from 2026 US national averages. Entering a ZIP scales labor to your state's roofer wages (BLS data), which closes much of the gap, but a local quote can still fall outside the range on a very cut-up roof or in an expensive metro area.
Where do the prices come from?
Each material has a 2026 US national-average price per square, split into material and labor. Material is priced on the waste-adjusted squares, labor on the actual squares, and tear-off adds $100 to $150 per square per layer. Add a ZIP code and labor moves up or down with your state's roofer wages from the Bureau of Labor Statistics.
Does the address lookup measure my roof?
No. It finds the building's footprint on OpenStreetMap and fills in length and width. You still enter the pitch and overhang, so check the dimensions before ordering materials.
Why won't it price shingles on my low-slope roof?
Code sets minimum slopes: 2/12 for asphalt shingles, 2.5/12 for concrete and clay tile, 3/12 for wood shakes and 4/12 for slate (natural or synthetic). Below those slopes it won't price them. On a very flat roof, pick TPO, EPDM or modified bitumen instead.
Is the calculator free?
Yes. It's free to use with no account, and you can bookmark or share an estimate because your inputs are saved in the page link.
Estimate your roof for free
No sign-up is required, and it works on any device.
If you only need one number, such as shingle bundles, gutter size or attic vents, there are 8 smaller standalone roofing calculators for that.