Use this construction calculation for preliminary quantity, geometry, material, load, or coverage planning when dimensions and units have been measured consistently.

Horizontal run (m)

Required number input.

Vertical rise (m)

Required number input.

Find the straight-line rafter length between eave and ridge from horizontal run and vertical rise; excludes overhang and cuts. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Theoretical rafter length (m)

The resulting theoretical rafter length returned as a number.

• A quantity estimate or simplified engineering formula is not a building-code check, stamped design, manufacturer approval, or site inspection. Material properties, tolerances, waste, moisture, workmanship, loads, local conditions, and code requirements can change the result.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Verify dimensions on site, use current product data and local code requirements, include an explicit waste or safety allowance where appropriate, and obtain qualified structural, electrical, plumbing, or geotechnical review when required.

• Roof Pitch Angle

  Calculate a roof slope angle from vertical rise and horizontal run, not the rafter length.

• Valley Flashing Length

  Estimate straight flashing length along a roof valley from its horizontal plan projection and vertical rise.

• Excavation Slope Ratio

  Horizontal run per unit vertical rise of an excavation slope; this geometric ratio is not a safe-slope determination.