Do I have to re-enter roof area for shingles and sheathing?
No. Roof length, rise/run/pitch, and overhang are entered once and the resulting roof area feeds both Shingles and Sheathing automatically.
Roofing Calculator
Enter your roof measurements once and get rafter count, roof pitch, shingle bundles, and sheathing sheets together — no re-entering the same numbers on three different pages.
Material List
Roofing jobs touch at least three separate takeoffs: framing/rafter count, roof covering, and sheathing. This page runs all three from one set of roof measurements. Each calculator below is the same one available on its own page — nothing here is a new formula, it is the Roof, Shingles, and Sheathing calculators reading from a shared input set.
How to measure your roof
Measure roof length along the eave (the horizontal edge, not the sloped side) and record it as one plane at a time — a simple gable roof has two planes of the same length. For rise and run, measure from the ridge to the wall plate: run is the flat horizontal distance, rise is the vertical height gained over that run. If you already know the pitch (for example, “6 in 12”), you can enter pitch and run instead and skip measuring rise directly.
On-center spacing is the distance between the centerlines of adjacent rafters or trusses, almost always 16 or 24 inches on residential work — check your framing plan or existing rafters before assuming. Overhang run is the horizontal distance the roof extends past the wall, measured the same way as the main run.
Eave, rake and ridge lengths are measured for that same single plane, so that the trim and the covering on the results below are counted on one basis and can be added up together. This plane’s eave is the horizontal bottom edge; its rakes are the two sloped end edges (usually twice the rafter length on a gable plane). The ridge is the one edge two planes share — the cap goes on it once, so enter the ridge on one plane and leave it blank on the other rather than counting it on both.
Roof measurements (one plane)
Enter these once, for one roof plane — the covering, the sheathing, the rafters and the eave/rake/ridge trim are all sized for that same plane, so they can be added up together. Rafter count and roof area come from the Roof calculator; that roof area then feeds Shingles and Sheathing automatically below. For a gable, run the page once per slope; the ridge is the one edge shared between them, so count it on one slope only.
Roof
Solves rise, run, pitch, rafter length, rafter count, roof plane area, ridge board length, eave fascia, and soffit area.
Plan for a — ft rafter at a —:12 pitch.
Plan for
Roof result
Warnings
- ERROR Enter a roof length greater than zero.
- ERROR Rise and run are required for the selected solve mode.
- INFO This is a general reference only. Verify local code, loading, and manufacturer requirements.
Detail values
- Rise
- — ft
- Run
- — ft
- Rafter length
- — ft
- Ridge-cut rafter length
- — ft
- Total rafter length (order length)
- — ft
- Pitch
- — : 12
- Angle
- — deg
- Recommended rafter size
- Data not available for this combination
- Span lookup status
- —
Assumptions
- Pitch warning reference: IRC R905.2.2: asphalt shingles, 2:12 minimum, with double underlayment required from 2:12 up to 4:12
- Overhang included in roof area: No
- Ridge board thickness: 1.5 in (1.5 in default matches a standard 2x ridge board)
- Rafter span table load basis: IRC "Rafter Spans for Common Lumber Species" table: 20 PSF roof live load, 10 or 20 PSF dead load, L/delta=180, ceiling not attached to rafters. Not a ground-snow-load table.
- Rafter span measured as: Horizontal run, wall to ridge — not yet entered. Overhang is a cantilever past the support and is not part of the span, and the table is not indexed by sloped length.
Formula details
- Rafter length: sqrt(rise^2 + run^2)
- Pitch: (rise / run) x 12
- Angle: atan(rise / run) x (180 / pi)
- Rafter count: ceil(roofLength / spacing) + 1
Layout arithmetic, not a published figure: one rafter at every on-center position along the plane, plus one to close the last bay. Per single roof plane -- multiply by the number of planes (2 for a gable, more for a hip) for the whole roof.
- Ridge-cut rafter length: rafterLength - (ridgeBoardThickness / 2) x (rafterLength / run)
Shortens the theoretical rafter length by the ridge board's half-thickness, projected onto the slope, so the ordered board matches the actual birdsmouth/ridge cut.
- Roof plane area: roofLength x (rafterLength + overhangDiagonal)
Single roof plane, including the overhang. Measured on the theoretical rafter length rather than the ridge-cut length: the ridge cut is where the board stops, and the covering runs over it to the ridge centerline.
- Soffit area: roofLength x overhangRun
Underside of the overhang only; zero when no overhang is entered.
- Rafter span lookup: Use verified IRC "Rafter Spans for Common Lumber Species" table row for species, rafter size, and spacing.
Roof live load 20 PSF, L/delta=180, ceiling not attached to rafters. Not a snow-load table.
Shingles
Converts roof area into bundles or metal panels to buy, plus starter strip, drip edge, ridge cap, and underlayment.
You'll need shingles of shingles for 0 sq ft of roof.
You'll need
Shingles result
Warnings
- ERROR Enter a roof area greater than zero.
- INFO Enter eave, rake, ridge, hip, and valley lengths to size starter strip, drip edge, cap shingles, and valley flashing. These are skipped without them.
Not counted -- answer these to add them
- Ridge and soffit ventilation
- The attic floor area. IRC R806.2 sizes ventilation against the flat ceiling below, not the sloped roof above, so the roof area entered here cannot stand in for it.
Detail values
- Roof area used
- 0 sq ft
- Squares
- —
- Adjusted squares
- —
Assumptions
- Shingle type: Architectural / dimensional
- Coverage input: Bundles per square
- Estimated waste: 10% for an average project
- Underlayment coverage: 400 sq ft per roll -- a No. 15 felt roll (36 in x 144 ft) after its salvage lap. Synthetic underlayment usually ships nearer 1,000 sq ft; check the wrapper and change this.
- Valley flashing lap: valley length not entered -- valley flashing not counted
- Ice barrier: not entered -- membrane not counted
- Ice barrier roll coverage: 200 sq ft per roll -- a 36 in x 66.7 ft roll. No field for it on this screen yet; check the wrapper before ordering.
- Underlayment cap fasteners: not entered -- cap nails/staples not counted
- Ventilation ratio: attic floor area not entered -- ventilation not sized
- Ridge vent net free area: not entered -- ridge vent not counted
- Intake vent net free area: not entered -- intake vents not counted
- Fasteners: 320 per square -- four nails into each of the ~80 strip shingles a square takes at a 5 in exposure (IRC R905.2.6 minimum)
Formula details
- Squares: roofArea / 100
- Adjusted squares: squares x (1 + wastePercent)
- Bundles to buy: ceil(adjustedSquares x bundlesPerSquare)
- Drip edge: eaveLength + rakeLength
- Ridge cap: ridgeLength + hipLength
Cap shingles run the ridge and every hip off the same bundle, so they are one length. A hip roof's hips are often longer than its ridge, and the roof area cannot tell them apart -- a gable and a hip roof of equal area measure the same.
- Valley flashing: valleyLength + (ceil(valleyLength / stockLength) - 1) x endLap
One end lap at each joint between 10 ft pieces. The 6 in lap is a common manufacturer installation instruction, not an IRC dimension -- the code sends you to the manufacturer's instructions for valley lining. Check your product and change it here if it differs.
- Underlayment rolls: ceil(adjustedArea / coveragePerRoll)
- Ice barrier area: (eaveLength x 3 ft per course x courses) + (valleyLength x 3 ft)
IRC R905.1.2. Required only where there is a history of ice forming along the eaves. Where it is required, each valley gets one 36 in course down its centreline -- that 3 ft is the membrane's own width, not a second assumption about how far up the valley it runs.
- Required net free vent area: atticFloorArea / 150 x 144
IRC R806.2. The 1/300 ratio applies only where BOTH exception conditions are met: 40 to 50 percent of the required ventilating area comes from ventilators in the upper portion of the attic, no more than 3 ft below the ridge measured vertically, with the balance at the eaves; and, in Climate Zones 6, 7 and 8, a Class I or II vapor retarder is installed on the warm-in-winter side of the ceiling. Otherwise the ratio is 1/150.
- Roofing nails: ceil(adjustedSquares x fastenersPerSquare)
IRC R905.2.6 sets not less than four fasteners per strip shingle, or two per individual shingle, as the minimum; six is required in high-wind areas and wherever the manufacturer says so. R905.2.5 governs the nail itself (gauge, head, penetration), not how many.
Sheathing
Converts roof area into sheathing sheets to buy, with OSB/plywood and roof/wall context for the thickness spec.
You'll need — sheathing panels for 0 sq ft.
You'll need
Sheathing result
Warnings
- ERROR Enter an area greater than zero.
Detail values
- Area used
- 0 sq ft
- Sheet area
- — sq ft
- Base sheets
- —
Assumptions
- Default panel size: 4 ft x 8 ft when unchanged
- Sheathing spec: 0.4375" OSB for roof sheathing (not a code minimum — verify local requirements)
- Estimated waste: 10% for an average project
Formula details
- Sheet area: sheetWidth x sheetLength
- Base sheets: area / sheetArea
- Purchase sheets: ceil(baseSheets x (1 + wastePercent))
Choosing shingles vs. metal roofing
Asphalt shingles are sold by the bundle, with roughly three bundles covering one “square” (100 sq ft) on a standard-weight product — check the wrapper for your specific product’s coverage rather than assuming three bundles per square. Standing seam metal is typically sold and estimated by panel; select the Metal panel shingle type above to switch the Shingles quantity to a panel count (roof area divided by your panel’s covered area, editable) instead of bundles — panels are commonly custom-cut to the rafter length, so confirm exact panel layout and length with your supplier.
Low-slope roofs need extra attention: most asphalt shingle manufacturers set a minimum reference pitch around 2:12 (with special underlayment below 4:12), and standing seam metal is commonly referenced around 3:12 minimum. This calculator flags a warning when your entered pitch is below those general reference points, but manufacturer installation instructions and local code always take precedence over a general reference.
FAQ
Can I still fine-tune just the shingles or sheathing numbers?
Yes. Flip a calculator to "Manual entry" to edit its inputs directly — for example if you're buying panels in a size the master inputs don't cover — without changing the roof geometry or the other calculators.
Why does a gable roof need this run twice?
This page calculates one roof plane at a time, matching the standalone Roof calculator — rafter count, roof area, shingle bundles, sheathing sheets, starter strip and drip edge are all sized for that single plane. For a gable roof, run it once per plane (they're usually identical) and double those totals. Ridge cap is the exception and is not doubled: two planes meet at one ridge and the cap goes on once, so enter the ridge length on one plane and leave it blank on the other. If you'd rather estimate a full gable building in one pass, use the Shed/Barn template — it applies the plane-count multiplier for you.
What does the pitch warning mean?
It's a general reference check against common manufacturer minimums for the covering material you selected, not a code determination. Always verify against your product's installation instructions and local code.
Disclaimer
Material estimate and general reference only. Verify local code, structural requirements, and manufacturer installation instructions before ordering or starting work.