Calculator
Drip Edge Calculator
Drip edge is bought by the piece, not the foot, and two things stand between a plan's eave and rake measurements and the piece count that actually ships: the rakes on a plan are horizontal runs, while drip edge is installed along the slope itself, and every piece after the first surrenders part of its length to the piece before it at the overlap.
This calculator corrects for both. It converts the rake's horizontal run into its true length up the slope using the roof's pitch, adds that to the eave length for a total run, then divides by what one piece actually advances the run once its overlap is subtracted — not by the piece's full nominal length, which overstates how far each piece really goes.
Calculate your quantity
Measured horizontally, as it appears on a plan.
Drip edge pieces
14 10 ft pieces
- Eave length
- 80 lin ft
- Rake horizontal run
- 48 lin ft
- Pitch multiplier
- 1.118 x
- Rake length up the slope
- 53.7 lin ft
- Total drip edge
- 133.7 lin ft
- Effective length per piece
- 9.83 ft
- Pieces if you ignore the laps
- 14 pieces
- Roofing nails
- 134 nails
- The rake measures 5.7 ft longer than its horizontal run at a 6/12 pitch. Measuring rakes off a plan view is the classic drip-edge shortfall.
Shopping summary
- • 14 x 10 ft drip edge
- • 1 lb of 1-1/4 in roofing nails
This is an estimate — confirm structural work with a professional.
How this calculation works
An eave runs level, so its length on a plan and its length on the roof are the same number. A rake runs up the slope from the eave to the ridge, so its horizontal run on a plan is shorter than its actual installed length by exactly the same pitch multiplier that inflates a roof's flat footprint into its true sloped area — the identical correction, applied here to a linear run instead of an area.
Once total run length is known, piece count follows from how far one piece actually advances that run, not its stated length. A 10 ft piece installed with a 2 inch overlap only extends the run by 9 ft 10 in, because the first two inches of the next piece sit underneath the one before it rather than adding new coverage. Ignoring that overlap and dividing straight by the nominal piece length is a small error per piece that adds up to a full extra piece over a long enough run.
- The pitch multiplier applies to rakes, not eaves — an eave measured on the ground is already the length that gets installed, while a rake measured the same way is not.
- Nail count follows total linear feet directly at a fixed spacing, independent of how that length is split across pieces, so it doesn't change if you switch between 10 and 12 ft stock.
- A steep roof with modest rakes and a shallow roof with long rakes can need similar total drip edge length for very different reasons — one from the pitch correction, the other from the run itself.
- This page assumes a straightforward eave-and-rake perimeter. Valleys, dormers and other roof breaks add drip edge or flashing this simple two-measurement model does not capture on its own.
The formula
rakeSlopeFt = rakeRunFt × pitchMultiplier; totalLinFt = eaveLinFt + rakeSlopeFt; effectivePerPiece = pieceLength − (overlap ÷ 12); pieces = ceil(totalLinFt ÷ effectivePerPiece)
- rakeRunFt × pitchMultiplier
- Converts a rake's horizontal run, the way it's measured on a plan or from the ground, into its true length up the slope — the multiplier is √(1 + (rise/12)²), the same ratio used to convert a roof's footprint into its sloped area.
- eaveLinFt
- Eave length needs no pitch correction, because an eave runs level along the bottom of the roof rather than up the slope.
- pieceLength − (overlap ÷ 12)
- How far one piece actually advances the total run once the overlap with the next piece is subtracted, converted from inches of overlap to feet.
- nailSpacing
- Fastener spacing along the total run, converted to a nail count independent of how the run is divided into individual pieces.
Dividing total run by a piece's nominal length instead of its overlap-adjusted length under-orders on any run long enough to need more than a handful of pieces — the shortfall is small per piece and compounds steadily as the run gets longer.
Where these numbers come from
- Pitch multiplier as √(1 + (rise/12)²)
- Geometric derivation from the roof's pitch triangle — rise over 12 inches of run sets the ratio between a rake's horizontal plan length and how much farther it actually measures once it is climbing the slope.
- 10 and 12 ft standard drip edge lengths
- Manufacturer-published — the common stock lengths drip edge is sold in at most suppliers. Custom lengths exist but are a special order rather than a stock item.
- 2 in standard overlap between pieces
- Trade convention for lapping drip edge sections so water sheds over the joint rather than finding it, similar in purpose to the head lap on rolled underlayment though a much smaller distance.
- 12 in nail spacing along drip edge
- Trade convention for fastening drip edge at a standard residential spacing. High-wind regions sometimes call for a tighter schedule, which is the reason nail spacing here is left adjustable rather than baked in as one fixed number.
Worked examples
A steep 10-in-12 roof with eave-dominated total length
| Total eave length | 120 ft |
|---|---|
| Total rake run | 60 ft |
| Roof pitch (rise per 12) | 10 in |
| Piece length | 10 ft |
| End overlap | 2 in |
| Nail spacing | 12 in |
| Drip edge pieces | 21 10 ft pieces |
|---|---|
| Eave length | 120 lin ft |
| Rake horizontal run | 60 lin ft |
| Pitch multiplier | 1.3017 x |
| Rake length up the slope | 78.1 lin ft |
| Total drip edge | 198.1 lin ft |
| Effective length per piece | 9.83 ft |
| Pieces if you ignore the laps | 20 pieces |
| Roofing nails | 199 nails |
At a 10-in-12 pitch, the 60 ft rake run measures about 78 ft up the actual slope — 18 ft longer than its horizontal run — bringing total drip edge length to roughly 198 ft. Dividing that by a full 10 ft piece would suggest 20 pieces; dividing by the overlap-adjusted 9 ft 10 in each piece really advances the run pushes the true count to 21, one more than the naive figure.
That single extra piece is the overlap correction working exactly as intended — on a run this length, ignoring the 2 inch overlap across enough pieces adds up to a full piece short, which is the gap between what a plan-measurement guess produces and what installing the material actually consumes.
A shallow 3-in-12 porch roof with rake-dominated total length
| Total eave length | 40 ft |
|---|---|
| Total rake run | 100 ft |
| Roof pitch (rise per 12) | 3 in |
| Piece length | 12 ft |
| End overlap | 1.5 in |
| Nail spacing | 8 in |
| Drip edge pieces | 13 12 ft pieces |
|---|---|
| Eave length | 40 lin ft |
| Rake horizontal run | 100 lin ft |
| Pitch multiplier | 1.0308 x |
| Rake length up the slope | 103.1 lin ft |
| Total drip edge | 143.1 lin ft |
| Effective length per piece | 11.88 ft |
| Pieces if you ignore the laps | 12 pieces |
| Roofing nails | 215 nails |
This porch's eave runs only 40 ft, a fraction of the first example's 120, yet its rake run is nearly double at 100 ft — and at only a 3-in-12 pitch, that long rake barely lengthens at all going up the slope, adding just 3 ft over its horizontal run. Total drip edge length still comes to about 143 ft, dominated almost entirely by the rake rather than the eave, the opposite balance from the first example.
Twelve-foot stock and a tighter 1-1/2 inch overlap here mean each piece effectively advances 11 ft 10 in of run, close enough to the nominal length that the naive piece count and the corrected one differ by only one piece rather than compounding further — worth noting that the size of the overlap correction depends on both the overlap chosen and how many pieces the run actually needs.
Common mistakes
- Measuring rake length off a plan or from the ground and using it directly, without applying the pitch multiplier. A plan view always understates a rake's true installed length, and the steeper the roof, the bigger that gap gets.
- Applying the pitch multiplier to the eave as well as the rake. Eaves run level and need no correction — only the rake, which climbs the slope, does.
- Dividing total linear footage by a piece's full nominal length instead of its overlap-adjusted length. It looks like a rounding difference on a short run and becomes a genuinely missing piece on a long one.
- Assuming nail count scales with piece count rather than total linear footage. Switching from 10 ft to 12 ft stock changes how many pieces you buy, but the nail count follows the total run length and spacing, not the piece count.
- Treating a roof with multiple pitches as a single pitch for the rake correction. Each differently-pitched section needs its own multiplier applied to its own rake run, not one averaged figure across the whole roof.
Shopping summary
Pieces and roofing nails both round up to the totals above — buy those directly rather than estimating from a partial run. None of it means much without real eave and rake numbers first: how to measure a roof walks through getting an honest pitch reading from the ground or the attic before this page's rake correction has anything reliable to work from.
Drip edge goes down before the underlayment on the eave and after it on the rake in most installation sequences — the roof underlayment calculator is the companion order for that layer, sized by a completely different lap-loss calculation rather than this page's perimeter-and-overlap one.
Ice barrier membrane at the eave, where cold climates require it, installs alongside this page's drip edge but is sized from an entirely different input — the ice and water shield calculator works from a horizontal code distance that climbs the roof's own pitch, not from eave and rake lengths at all.
FAQ
Why does the pitch multiplier apply to the rake and not the eave?
It's purely about which direction each edge travels relative to the slope, not which one is longer or more prominent on the roof. The size of the correction scales with pitch: at a gentle 4-in-12 it only adds a few percent to a rake's plan length, easy to round away by eye, while at a steep 12-in-12 it adds well over 40 percent, which is why skipping the multiplier hurts far more on a steep roof than a shallow one. A hip roof's diagonal hip lines aren't rakes at all and need their own separate measurement — this page's two-input model assumes a gable end.
How much does the overlap actually cost me on a typical order?
On a short run, often nothing — the rounding absorbs it. On a longer run it adds up to roughly one extra piece for every dozen or so pieces the naive nominal-length count would suggest, and this page's overlap-adjusted piece length is what catches that gap while the order is still on paper instead of on the roof.
Should I choose 10 ft or 12 ft drip edge stock?
Either works structurally; the choice mostly comes down to fewer overlap joints with the longer stock against easier handling and less waste on a roof with shorter runs between corners with the shorter stock. This page will show you the piece count either way once you enter the stock length you're working with.
Does drip edge go under or over the underlayment?
It varies by edge: at the eave, drip edge is typically installed first, directly on the deck, with underlayment lapped over it; at the rake, the more common sequence reverses, with underlayment first and drip edge over it. Check your underlayment manufacturer's instructions and local practice, since both sequences are used.
My roof has two different pitches. How do I handle the rake correction?
Run this calculator once per distinct pitch section, applying each section's own eave and rake measurements and its own pitch to get that section's piece count, then add the results together. Averaging pitches into one figure understates the steeper section and overstates the shallower one, and the two errors don't cancel evenly.
Does nail spacing change in high-wind regions?
Often yes — some wind-exposed areas call for tighter drip edge fastening than the standard 12 inch spacing this page defaults to. Check your local requirements and adjust the nail spacing field accordingly; the piece count itself doesn't change, only the nail total.
Where to go next
The projects this number is a step of, the guides that explain the method behind it, and the rest of its trade group.