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Roof squares & materials takeoff

Give it the footprint and the pitch. It returns the squares, and the bundles, rolls, pieces and boxes to put on the order — with the waste allowance shown, not buried.

How are you describing the roof?

Most jobs are one rectangle. Switch to sections for an ell, a dormer, a porch or more than one pitch.

Measure the roof, not the house. This is the footprint the roof covers from above, including the eave overhangs — not the heated floor area. It is the mistake that throws a takeoff out by two or three squares.

Slope factor 1.118×

Roof style

A hip roof runs eaves all the way round and needs cap on four hips, so it costs more in accessories.

The default residential shingle. GAF Timberline HDZ and equivalents.

Synthetic has to be fastened with plastic cap nails — GAF, Grace and TAMKO all require them — so a cap nail line is on the order below.

136 fasteners a square: 3 rows at 12 in o.c. plus 6 in o.c. at the laps.

105 ft only if you separate every sheet at the centre perforation. Run whole, a bundle covers 52.5 ft — pick the other Owens Corning line for that.

Cap runs from 20 to 45 ft a bundle depending on the product.

A coil carton holds far more than a hand-drive box of the same weight.

Flashing you have counted

Plumbing vent flashings, one per vent. Two to five on most houses — count them, nothing can derive it.

Dormer cheeks, chimney sides, where an ell meets a wall. Step flashing goes in one piece per shingle course, so 2.4 pieces a foot.

Fifty, not a hundred. Buying this one on a hundred-piece assumption leaves you half short.

Roof complexity

Waste is estimating practice, not a specification. The defaults are 10% simple and 15% cut up — override it with yours.

Required in high-wind zones and on mansards. Four is the standard-slope minimum.

Valleys plus the eaves. Required by code in many jurisdictions.

Roof area

Squares
13.42
1,342 sq ft of roof surface
With 10% waste
14.76sq
What to order against
Slope factor
1.118×
1,200 sq ft footprint
Eaves
80 ft
Rakes
67.1 ft
Ridge
40 ft
Hips
0 ft
Valleys
0 ft

Edge lengths derived from the footprint and pitch. The rakes climb the slope, so they are longer than the half-width they cover. A single rectangle has no valleys, which is why this one reads zero — switch to sections to measure them.

Materials to order

Materials to order
ItemNeededOrderSpare
Architectural (laminated)
3 bundles per square at 33.33 sq ft each
1,476sq ft45 bundles24 sq ft
Synthetic underlayment (10 sq roll)
1,409sq ft2 rolls425 sq ft
Plastic cap nails — 1 in plastic cap nails, 2,000 per box
Required for synthetic underlayment, not an upgrade. 3 rows at 12 in o.c. plus 6 in o.c. at the laps.
1,830ea1 box170 ea
Starter strip — Owens Corning Starter Strip Plus, split (105 ft)
Runs the eaves and the rakes. 105 ft only if you separate every sheet at the centre perforation. Run whole, a bundle covers 52.5 ft — pick the other Owens Corning line for that.
154ft2 bundles56 ft
Hip and ridge cap — GAF Seal-A-Ridge (25 ft)
Runs every ridge and every hip
42ft2 bundles8 ft
Drip edge (10 ft pieces)
Runs the eaves and the rakes
154ft16 pieces6 ft
Valley metal — W-valley, 10 ft pieces
Open valleys. The 5% is the 6 in end lap on a 10 ft piece, not cut waste.
0ft0 pieces—
Pipe boots (plumbing vent flashings)
One per plumbing vent. Count them off the roof — two to five on most houses.
3ea3 boots0 ea
Step flashing — 5 × 8 in aluminium, 50 per bundle
Fifty, not a hundred. Buying this one on a hundred-piece assumption leaves you half short.
0ea0 bundles—
Roofing nails — Coil carton (7,200 nails, approx. 31 lb)
4 nails per shingle, plus an allowance for starter, cap and drip edge
3,892ea1 carton3,308 ea

“Needed” includes the waste allowance. “Spare” is what is left over after rounding up to whole bundles, rolls and boxes — you are paying for it, so it is shown. A line whose measurement is zero orders zero, never a minimum.

Keep this one

The numbers above are free, now and always, on a tier that takes no card. Paying keeps more jobs live, puts your logo on the estimate, and drops the “Made with RoofParrot” line from the PDF you send.

See the plans — from $42 a seat a monthI have a key
The formula
slope factor = sqrt(rise² + run²) / run surface area = footprint area × slope factor squares = surface area / 100 order quantity = ceil( (surface area × (1 + waste)) / coverage per unit )

The footprint is the roof’s horizontal projection — what it covers seen from directly above, overhangs included. The slope factor is plain Pythagoras: the sloped surface is the hypotenuse of the rise-over-run triangle, so a 6/12 roof has 1.1180 square feet of surface for every square foot of footprint.

Each material is then its own small calculation: the measured quantity, times one plus the waste allowance, divided by what one purchasable unit covers, rounded up. What differs between them is only which measurement drives them.

What measurement drives each material
LineDriven by
ShinglesRoof area
UnderlaymentRoof area
Plastic cap nailsRoof area
Starter stripEaves + rakes
Hip and ridge capRidges + hips
Drip edgeEaves + rakes
Valley metalValleys
Pipe bootsBoots you count
Step flashingRoof-to-wall length
Field nailsShingles on the roof
Ice-and-waterValleys + eave courses
Two things that surprise people

A line whose measurement is zero orders zero, never a minimum. Leave the valley, wall and boot fields empty and those three lines read zero — the tool does not invent a number for something only a tape measure can answer.

The coverage figures are a picker, not a constant, because they vary more than people expect. Hip and ridge cap runs from 20 lineal feet a bundle to 45 depending on the product. Starter runs from 50 to 120, and GAF Pro-Start only reaches its 120.33 if you split every sheet in half. A coil carton of nails holds 7,200; a hand-drive box of roughly the same weight holds about 4,050. Pick what you actually buy.

Worked example: a 40 × 30 gable at 6/12
Footprint
40 ft × 30 ft
Pitch
6/12
Style
Gable
Shingle
Architectural
Waste
10% (simple)
  1. Footprint area. 40 × 30 = 1,200 sq ft.
  2. Slope factor. sqrt(6² + 12²) / 12 = sqrt(180) / 12 = 1.1180.
  3. Surface area. 1,200 × 1.1180 = 1,341.64 sq ft.
  4. Squares. 1,341.64 / 100 = 13.42 squares.
  5. Add waste. 13.42 × 1.10 = 14.76 squares. That is what to order against.
  6. Shingles. 1,341.64 × 1.10 / 33.33 sq ft per bundle = 44.28, so 45 bundles. The rule of thumb — round to 15 squares, 3 bundles each — gives 45 here too, but that is two roundings landing together rather than a check. On a slightly smaller roof the two disagree by two bundles, and the coverage figure is the one to trust.
  7. Underlayment. 1,341.64 × 1.05 / 917 sq ft net per roll = 1.54, so 2 rolls of synthetic.
  8. Plastic cap nails. Synthetic underlayment has to be cap-fastened, so: 3 rows at 12 in on centre plus the lap row at 6 in on centre is 5 fasteners per lineal foot of a 48 in roll, and the roll nets 44 in, so 5 × 12 / 44 = 1.364 per sq ft. 1,341.64 × 1.364 = 1,830 fasteners, which is 1 box of 2,000. No waste allowance on top — the row count already comes from the stricter sealed-deck pattern.
  9. Starter. Eaves 80 ft plus rakes 2 × 30 × 1.1180 = 67.08 ft, so 147.08 ft. × 1.05 / 105 ft per bundle = 1.47, so 2 bundles — on the default, which is Starter Strip Plus with every sheet split at its centre perforation. Run the sheets whole and a bundle covers 52.5 ft, which is 3 bundles; the picker has both readings and the order follows the one you choose. Starter runs the rakes as well as the eaves — GAF's warranty lists “Starter Strip Shingles (Eaves & Rakes)” as a qualifying accessory, so skipping the rakes costs the homeowner the wind coverage they were sold.
  10. Ridge cap. Ridge is 40 ft. 40 × 1.05 / 25 ft per bundle = 1.68, so 2 bundles of Seal-A-Ridge. On TimberTex at 20 ft a bundle it would be 3.
  11. Drip edge. The same 147.08 ft of eave and rake. × 1.05 / 10 ft per piece = 15.44, so 16 pieces.
  12. Nails. 33.33 / 21 pieces = 1.587 sq ft per shingle, so 1,341.64 / 1.587 = 846 shingles installed. 846 × 4 nails × 1.15 = 3,892, which is one 7,200 coil carton. The 15% here covers starter, cap and drip-edge nailing, which the field count does not.

14.76 squares to order against: 45 bundles of architectural shingles, 2 rolls of synthetic underlayment, 1 box of plastic cap nails, 2 bundles of starter, 2 bundles of hip and ridge cap, 16 pieces of drip edge and 1 carton of nails. Valley metal and step flashing read zero on this one: a rectangular gable has no valleys and no roof-to-wall line. The pipe boots are whatever you counted.

Figures from Roof Online — roof pitch factor table; GAF Timberline HDZ — 33.33 sq ft per bundle, 3 per square; Owens Corning Starter Strip Plus — 105 lineal ft per bundle once the sheets are split, 52.5 ft run whole; GAF — starter at eaves and rakes is a warranty condition; GAF Seal-A-Ridge — 25 lineal ft per bundle; GAF TAB-R-180 — synthetic underlayment needs cap fasteners; FORTIFIED FH 2023-11 — 3 rows at 12 in o.c., 6 in o.c. at the laps; Gibraltar V18G — W-valley, 18 in × 10 ft; IKO — step flashing at every course; 6 in valley metal end laps.

Questions

Is the footprint the same as my house's square footage?
No, and this is the mistake that throws a takeoff out most often. The footprint here is the area the roof covers seen from above, including the eave overhangs. A 1,200 sq ft single-storey house with 18 in overhangs covers appreciably more than 1,200 sq ft of ground, and a two-storey house of 2,400 sq ft of floor area may have a 1,200 sq ft roof footprint.
Why is my roof area bigger than the footprint?
Because the roof is sloped. A 6/12 pitch gives 1.1180 sq ft of roof surface for every square foot of footprint; a 12/12 gives 1.4142. The multiplier is the slope factor, and it comes straight from Pythagoras on the rise and the run.
What waste allowance should I use?
10% is the common default on a simple gable and 15% on a hip or cut-up roof with several valleys. Both are estimating practice rather than a published specification, which is why the field is editable and the figure is shown on the result rather than hidden inside it. Use your own number if you have one — you know your own cut waste better than any calculator does.
Why does the hip roof need so much more ridge cap?
A hip roof caps four hips as well as the ridge. On the 40 × 30 example at 6/12 the gable needs 40 ft of cap and the hip needs 100 ft — ten feet of ridge plus four hips of 22.5 ft each. The hip roof also runs eaves round the whole perimeter instead of along two sides, so it needs more starter and more drip edge too.
How are the nails worked out?
From the shingles that actually go on the roof, not the ones you buy. The measured surface area is divided by the area one shingle covers, then multiplied by four nails per shingle — or six for high-wind nailing. Four is the IRC minimum and the manufacturers' baseline; the six-nail rule is the manufacturer's, and it is a warranty condition rather than a code requirement, so read your shingle's instructions rather than ours. A 15% allowance on top covers starter, cap and drip-edge nailing, which the field count leaves out.
Why does it ask which starter and which cap I am buying?
Because they differ more than anything else on the list. Hip and ridge cap runs from 20 lineal feet a bundle (GAF TimberTex) to 45 (CertainTeed Shadow Ridge) — a bundle count that is out by more than double between two perfectly ordinary products. Starter runs from 50 feet a bundle to 120.33, and GAF Pro-Start only reaches 120.33 if you split every sheet in half, which is easy to not do. Picking one number for everyone would mean most people are short.
Why does starter run the rakes as well as the eaves?
Because the wind warranty says so. GAF's residential warranty lists the qualifying accessory as “Starter Strip Shingles (Eaves & Rakes)”, and for shingles without the LayerLock feature it wants six nails as well as starter on both. Running starter only at the eaves is cheaper by a bundle and costs the homeowner the wind coverage they were sold, which is a conversation nobody wants three years later.
Does it handle more than one pitch, or dormers?
Yes. Switch the form to “Several sections” and add a section for each roof area, each with its own dimensions and pitch; the areas are summed and the slope factor reported is the area-weighted mean. In that mode you also enter the edge lengths yourself — eaves, rakes, ridges, hips and valleys — because the shape that needs this mode is the shape the rectangle arithmetic gets wrong. One rectangle stays the default, since most jobs are one rectangle.
Why does the valley only appear in sections mode?
Because a rectangle has no valleys. A valley is where two roof planes meet, so the single-rectangle form could never produce a number for one — and until the sections mode existed, valley metal and valley ice-and-water were silently zero on every job. In sections mode the valley footage is a measurement you take, and it drives the valley metal (10 ft W-valley pieces) and the ice-and-water that goes underneath it.
Why are plastic cap nails on the list, and only sometimes?
Because synthetic underlayment requires them and felt does not. GAF's technical bulletin R-180 specifies cap nails or cap staples and allows uncapped fasteners only when every one of its conditions holds — code compliance, the shingles on the same day, no weather expected, and a slope under 6/12. Grace Syn 15 says uncapped nails and staples cannot be used; TAMKO prints the cap locations on the sheet; Owens Corning ProArmor wants a 1 in minimum cap diameter. The default underlayment here is synthetic, so the count is worked out at 136 fasteners a square — 3 rows at 12 in on centre plus 6 in on centre at the laps, over the 44 in a 48 in roll nets. Choose felt and the line disappears.
How many pieces of step flashing is a foot of wall?
2.4, because step flashing goes in one piece per shingle course and 12 divided by a 5 in exposure is 2.4. An architectural shingle's 5⅝ in exposure needs only 2.13, so 2.4 over-orders by about 12% on the commonest shingle — the safe direction for a box of a hundred. Watch the pack size: a galvanized box is 100 pieces and an aluminium bundle is 50, which is why it is a picker rather than a constant.

What this list does not include

Shingles, underlayment, cap nails, starter, hip and ridge cap, drip edge, valley metal, pipe boots, step flashing and field nails are all on the list, and ice-and-water when you ask for it. These are not, and they are deliberately absent rather than forgotten:

  • Counter flashing, apron flashing and a chimney cricket. Step flashing is counted off the roof-to-wall length you enter; the counter flashing that caps it, the apron at a wall that runs across the slope, and a cricket behind a wide chimney are all separate and none of them is here. A cricket in particular is a framed, site-measured thing, not a stock part.
  • Ridge vent as a material. The attic ventilation calculator sizes it; this list does not carry it across.
  • Decking replacement, which nobody knows until the roof is open, and is the single biggest cost surprise on a re-roof. Quote it as a contingency with an agreed unit price.
  • Roof cement and sealant, dumpster and disposal, and anything to do with gutters.
  • Anything the tool cannot measure for you. The valleys, the roof-to-wall length and the pipe-boot count are inputs, not outputs. Leave them at zero and those lines read zero — which is the tool declining to guess, not an omission.

The storm and insurance checklist lists the items that most often get left off a scope, including several of these.

Roof measuring tool — squares and what to order · RoofParrot