Measure two lengths before ordering drip edge: the eaves and the rakes. A simple gable roof has 2 horizontal eaves and 4 sloped rakes, and the rakes are longer than the flat footprint width because the slope adds length. Measuring each run at the roof surface keeps the order accurate.
How do you measure a roof for drip edge?
Add up every eave and rake along the roof surface. Measure eaves with a tape along the horizontal edge, scale each rake by the roof pitch multiplier, then convert each run into whole 10 ft pieces with the 2 in overlap subtracted at each joint.
Total edge length = sum of eave runs + sum of rake runs
Which edges need drip edge?
The 2021 International Residential Code, Section R905.2.8.5, requires drip edge at the eaves and rake edges of shingle roofs. Count the edges by roof shape before measuring.
| Roof shape | Edges to measure | Notes |
|---|---|---|
| Simple gable | 2 eaves, 4 rakes | Scale each rake by the pitch multiplier |
| Hip | All eaves, usually 4 or more | Eave length is not changed by the slope |
| Shed | 2 eaves (high and low), 2 rakes | Scale each rake by the pitch multiplier |
| With dormers or additions | Each added eave and rake | Measure separately; do not assume they match the main roof |
An eave is the horizontal edge at the bottom of a roof slope. A rake is the sloped edge running from the eave to the ridge on a gable end.
How do you calculate rake length from roof pitch?
Measure the building width on the ground, halve it, and multiply by the roof pitch multiplier. The multiplier for a 6-in-12 pitch is 1.118, so each foot of half-width becomes 1.118 ft along the slope.
Rake slope length = (building width ÷ 2) × pitch multiplier
Pitch multiplier = sqrt(1 + (rise ÷ run)²)
| Roof pitch | Pitch multiplier |
|---|---|
| 4 in 12 | 1.054 |
| 5 in 12 | 1.083 |
| 6 in 12 | 1.118 |
| 7 in 12 | 1.158 |
| 8 in 12 | 1.202 |
| 9 in 12 | 1.250 |
| 10 in 12 | 1.302 |
| 12 in 12 | 1.414 |
Worked example: a gable roof
A house footprint measures 40 ft by 28 ft with a 6-in-12 pitch. The eaves run along the 40 ft sides.
- Pitch multiplier for 6 in 12: 1.118.
- Rake slope length: 28 ÷ 2 = 14 ft; 14 × 1.118 = 15.65 ft.
- Two eaves: 2 × 40 = 80 ft.
- Four rakes: 4 × 15.65 = 62.6 ft.
- Total edge length: 80 + 62.6 = 142.6 ft (about 43.5 m).
How many drip edge pieces should you order?
Drip edge is commonly sold in 10 ft lengths. The code requires adjacent segments to overlap at least 2 in, so one 10 ft piece covers 9.83 ft once joined. Divide each measured run by 9.83 ft and round up, because pieces do not span corners.
Pieces per run = run length ÷ (10 ft − 2 in), rounded up
Effective coverage per piece = 9.83 ft (3.00 m)
For the worked example: each 40 ft eave needs 40 ÷ 9.83 = 4.07, rounded to 5 pieces, so 10 pieces for both eaves. Each 15.65 ft rake needs 15.65 ÷ 9.83 = 1.59, rounded to 2 pieces, so 8 pieces for the 4 rakes. Order 18 pieces total. Confirm the actual selling length on the product label before counting.
Common measuring mistakes
- Measuring the flat footprint width instead of the sloped rake length.
- Counting only the eaves and forgetting the rakes.
- Rounding the total length to whole pieces without splitting runs first.
- Counting each 10 ft piece as 10 ft of coverage and ignoring the 2 in overlap at every joint.
- Using one pitch value for a roof with additions or dormers at a different pitch.
- Measuring a sagging old edge instead of the straight run along the fascia line.
Code and product limits
The measurement method works for any roof shape, but the code rule it follows is specific: IRC Section R905.2.8.5 covers shingle roofs, and local amendments can change the requirement. The code also requires the drip edge to extend at least 1/4 in below the sheathing and 2 in back onto the deck, and to be fastened at not more than 12 in on center. Those dimensions do not change the piece count, but the wrong profile can still fail inspection.
Work from the ground where possible. Roof edges mean ladders, and a tape stretched along a long rake is easier and safer with a second person holding the far end. Measure straight runs along the fascia line.
Sources and scope
- International Code Council, 2021 International Residential Code, Section R905.2.8.5 "Drip edge": drip edge required at eaves and rake edges of shingle roofs; 2 in (51 mm) minimum segment overlap; 1/4 in (6.4 mm) below the sheathing and 2 in (51 mm) back onto the deck; fastening at not more than 12 in (305 mm) on center; underlayment over the drip edge at eaves and under it at rakes.
- Professional Roofing (NRCA), "On the edge", 2019-06-01: IBC and IRC drip edge requirements and industry recommendations.
- 2012 IRC significant-changes summary: drip edge usually manufactured in 10 ft lengths; first required by the 2012 IRC for asphalt shingles.
Scope: the methods here measure roof edge length and piece counts from stated dimensions and selling lengths. The governing code, local amendments, shingle manufacturer instructions, product label, and a qualified installer control the accepted profile, fasteners, and final order.
Review responsibility: Saleem Sial owns the published calculation, source, and editorial checks. Waseem Sial, External Reviewer and Engineer, remains listed for ongoing external review; no completed external-review date is claimed.
Next, use the roof area measurement guide to convert these edges into a sloped surface area, or check a pitch value against the roof pitch multiplier chart. For the full set of planning tools, return to the Roofing Calculators hub.
