Free Roof Valley Calculator: Estimate Costs & Materials
Turn plan legs into valley LF and a rough idea of peel-and-stick strips before you detail the job.
Valley length (plan legs model)
When each roof face meets at a right angle, the valley centerline in plan is often the hypotenuse of the two horizontal runs to the corner. Multiply by the number of similar valleys.
Real installs overlap strips—this is a rough piece count from length ÷ width; follow your detail and manufacturer.
Valley & I&W hints
Enter legs, valley count, and strip width, then click Calculate.
How to Calculate Roof Valley Calculator Manually
Step 1: Establish the Horizontal Plan Geometry
On a plan drawing, identify the two run distances that meet at the valley or hip corner. For a 90° plan corner, these are the two eave-to-ridge runs from each intersecting plane.
Step 2: Calculate Valley Centerline Length (Plan View)
For a 90° corner where Leg A and Leg B are the horizontal runs: Valley plan length = √(A² + B²). If Leg A = 16 ft and Leg B = 22 ft, valley plan = √(256+484) = √740 ≈ 27.2 ft.
Step 3: Convert Plan Valley to Sloped Valley Length
Apply the slope factor for the valley pitch. For a symmetric hip at 6/12 pitch: multiply plan valley length by √(1 + (6/12)²) = 1.118. So 27.2 × 1.118 ≈ 30.4 ft of actual valley metal or I&W shield needed.
Step 4: Scale for Multiple Identical Valleys
Multiply by the number of identical-geometry valleys. On a simple four-way hip, you'll have 4 valleys. On a T or L plan, count each re-entrant corner as a separate valley with its own geometry.
Step 5: Size Accessory Quantities from Valley Length
Ice & water shield in valleys: order LF ÷ roll width (usually 3 ft wide = 1 roll per 3 LF of valley). Valley metal: order LF of W-metal or Z-metal from the centerline length plus 12" overhang at eave.
Roof Valley Calculator Formulas
- Valley plan length = √(Leg A² + Leg B²) [Pythagorean theorem for 90° plan corner]
- Sloped valley length = Valley plan length × Slope factor [slope factor = √(1 + (rise/run)²)]
- I&W shield strips = ceil(Total valley LF ÷ Roll width in ft) [e.g. 3 ft wide roll]
Valley geometry assumes right-angle plan corners. Obtuse or acute plan corners require trigonometric adjustment. Always measure the actual valley centerline on the roof deck before cutting valley metal or flashing.
Roof Valley Calculator: Plan Legs, Valley Lineal Feet, and Peel-and-Stick Strip Planning
Hypotenuse from Two Perpendicular Eave Runs
When two horizontal eave directions meet at an inside corner at roughly 90°, the valley centerline in plan often behaves like the hypotenuse of a right triangle: √(A² + B²) from the legs you measured. Multiplying by valley count scales repeated identical valleys. Field-verify when the plan is not square or valleys are unequal.
Strip Counts Bracket Peel-and-Stick from Width and Valley LF
Enter the effective width you run parallel to the valley per strip. The tool divides total valley LF by that width to suggest how many strip-width passes to budget—still a planning bracket because overlaps, jogs, and detail widths change real consumption.
Plan Legs Ignore 3D Lengthening—Steep Jobs Need a Field Check
Inputs are horizontal. True valley length in 3D lengthens with pitch and detail. On very steep or irregular valleys, treat output as a starting point and adjust from ladder measure or CAD.
Pair Valley LF with the Linear Foot Calculator for Full Perimeter Scope
After valleys look sane, roll eave, rake, ridge, and hip totals on the linear foot calculator for roof. For sloped area by facet, use the roof plane calculator.
Frequently Asked Questions — Roof Valley Calculator
Hypotenuse assumptions, identical valleys, ice barrier width, open versus closed valleys, and shingle waste.
How Do You Calculate Roof Valley Length from Two Sides?+
When plan legs meet at ninety degrees, valley centerline length often equals √(A² + B²)—then multiply by identical valley count. For better estimating accuracy, cross-check pitch geometry, plane intersection, and field verification with your project notes, then confirm layout accuracy before final ordering. This keeps your material planning aligned with real site conditions and reduces costly quantity revisions.
Why Is Roof Valley Length a Hypotenuse in Plan View?+
The valley traces the shortest line across the inside corner in the flat map, so right-triangle math matches many field sketches. For better estimating accuracy, cross-check pitch geometry, plane intersection, and field verification with your project notes, then confirm layout accuracy before final ordering. This keeps your material planning aligned with real site conditions and reduces costly quantity revisions.
Does This Roof Valley Calculator Assume Every Valley Matches?+
Yes—repeat the same legs and count; for unequal valleys, run separate calculations instead of one blended count. For better estimating accuracy, cross-check pitch geometry, plane intersection, and field verification with your project notes, then confirm layout accuracy before final ordering. This keeps your material planning aligned with real site conditions and reduces costly quantity revisions.
Are Peel-and-Stick Strip Counts from the Valley Calculator Exact?+
No—they bracket parallel strips from width and LF; overlaps, jogs, and code widths still change real ice-and-water usage. For better estimating accuracy, cross-check pitch geometry, plane intersection, and field verification with your project notes, then confirm layout accuracy before final ordering. This keeps your material planning aligned with real site conditions and reduces costly quantity revisions.
Open Valley Versus Closed Valley—Does LF Change Much?+
Lineal feet along the valley may be close, but flashing width, weave, and metal differ—follow the shingle manufacturer detail. For better estimating accuracy, cross-check pitch geometry, plane intersection, and field verification with your project notes, then confirm layout accuracy before final ordering. This keeps your material planning aligned with real site conditions and reduces costly quantity revisions.
What If I Already Measured Valley LF on the Roof?+
Skip hypotenuse mode and type that LF into the linear foot calculator with your other eave, rake, and ridge runs. For better estimating accuracy, cross-check pitch geometry, plane intersection, and field verification with your project notes, then confirm layout accuracy before final ordering. This keeps your material planning aligned with real site conditions and reduces costly quantity revisions.
Does Roof Pitch Change Valley Length from Plan Legs?+
Plan legs ignore 3D slope lengthening—verify steep or irregular valleys with ladder measure or CAD before you lock orders. For better estimating accuracy, cross-check pitch geometry, plane intersection, and field verification with your project notes, then confirm layout accuracy before final ordering. This keeps your material planning aligned with real site conditions and reduces costly quantity revisions.
What Ice Barrier Width Should I Enter for Valley Strips?+
Use the effective width in feet you actually run parallel to the valley per manufacturer and local code guidance. For better estimating accuracy, cross-check pitch geometry, plane intersection, and field verification with your project notes, then confirm layout accuracy before final ordering. This keeps your material planning aligned with real site conditions and reduces costly quantity revisions.
Do Valleys Add Shingle Waste Beyond Valley LF?+
Yes—cuts and weave consume extra field shingles, so bump waste on the bundle order after you trust valley geometry. For better estimating accuracy, cross-check pitch geometry, plane intersection, and field verification with your project notes, then confirm layout accuracy before final ordering. This keeps your material planning aligned with real site conditions and reduces costly quantity revisions.
How Do Roof Valley Calculations Tie to Drip Edge Orders?+
Valley LF feeds accessory planning—pair totals with the linear foot calculator so metal, ice, and cap lines stay separate. For better estimating accuracy, cross-check pitch geometry, plane intersection, and field verification with your project notes, then confirm layout accuracy before final ordering. This keeps your material planning aligned with real site conditions and reduces costly quantity revisions.