Enter the gutter width, downspout width, gutter height, and downspout height into the calculator to estimate the combined cross-sectional opening area (a geometric check) based on those dimensions. Note: actual conductor/leader head sizing for roof drainage is typically based on roof drainage area, design rainfall intensity, and the leader/downspout capacity per local code/manufacturer data.

Conductor Head Size Calculator

Enter any 4 values to calculate the missing variable

Related Calculators

Conductor Head Opening Area Formula

The following geometric relationship can be used to estimate a combined opening (cross-sectional) area from the gutter and downspout dimensions. This is not a roof-drainage sizing method; for actual leader head sizing, use roof drainage area, design rainfall intensity, and applicable code/manufacturer tables.

CHS = (GW \times GH) + (DW \times DH)

Variables:

  • CHS is the conductor head opening area (e.g., in², ft², cm², or m²)
  • GW is the gutter width
  • DW is the downspout width
  • GH is the gutter height
  • DH is the downspout height

To estimate CHS, multiply the gutter width by the gutter height, multiply the downspout width by the downspout height, and add the two areas together. Use consistent length units for GW, DW, GH, and DH.

What is a Conductor Head?

A conductor head, also known as a leader head or collector box, is a component of a rainwater drainage system. It is typically installed at the top of a downspout (leader) to collect and direct water from the gutter system into the downspout. Conductor heads are often used to help manage high flows at an outlet and can provide an aesthetic, decorative element on the exterior of a building.

How to Calculate Conductor Head Size?

The following steps outline how to calculate the Conductor Head Opening Area (CHS) using the geometric relationship above.

  1. Determine the gutter width (GW).
  2. Determine the gutter height (GH).
  3. Determine the downspout width (DW).
  4. Determine the downspout height (DH).
  5. Calculate CHS using: CHS = (GW × GH) + (DW × DH).
  6. After inserting the values and calculating the result, you can verify with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge (assume all dimensions are in inches).

Gutter Width (GW) = 10

Downspout Width (DW) = 5

Gutter Height (GH) = 8

Downspout Height (DH) = 6

CHS = (10 × 8) + (5 × 6) = 80 + 30 = 110 in²