Use the tabs in the calculator to select a surface geometry and enter the requested dimensions to compute a radiation view factor. The “Small Surface Approx” tab uses a small-solid-angle approximation (valid when surface 2 appears small from surface 1). Other tabs use closed-form view factor expressions for specific shapes. The “Heat Exchange (Q)” tab estimates net radiative heat transfer between two diffuse-gray surfaces that exchange radiation only with each other.

Radiation View Factor Calculator

Small Surface Approx
Parallel Rectangles
Perpendicular Rectangles
Disk → Cylinder
Heat Exchange (Q)

Small-solid-angle approximation: surface 1 is very small (differential) and surface 2 is relatively small and far away, directly facing (F12 ≈ A2/(π d²); best when A2 ≪ π d²).

Results
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Radiation View Factor Formula

In general, the view factor between two finite surfaces depends on their geometry and relative orientation (and is not determined only by areas and a single distance). For the calculator’s Small Surface Approx tab, the following small-solid-angle approximation is used when surface 2 appears small from surface 1 and the surfaces are directly facing.

F_{12} \approx \frac{A_2}{\pi d^2}

Variables:

  • F_{12} is the view factor from surface 1 to surface 2 (dimensionless, 0 to 1)
  • A_2 is the area of surface 2 (m²)
  • d is the line-of-sight separation between the surfaces (approximately the distance between centroids when the surfaces are small compared with d) (m)

To use this approximation, divide the area of surface 2 by the square of the separation distance and then divide by π. If the computed value is not much less than 1, the approximation may be inaccurate and a geometry-specific view factor (like the other calculator tabs) should be used instead.

What is a Radiation View Factor?

The radiation view factor, also known as the configuration factor or shape factor, is a dimensionless quantity used in radiative heat transfer calculations. It represents the fraction of the radiation leaving one surface that directly reaches another surface. The view factor depends on the geometry of the surfaces and their relative orientation. It is a critical component in calculating radiative heat exchange between surfaces.

How to Calculate Radiation View Factor?

The following steps outline how to calculate the Radiation View Factor using the small-solid-angle approximation shown above.

  1. Determine the area of surface 2 (A_2) in square meters.
  2. Determine the separation distance d (in meters).
  3. Use the approximation F_{12} ≈ A_2 / (π d^2).
  4. Confirm the result is well below 1 (i.e., surface 2 subtends a small solid angle); otherwise use a geometry-specific view factor (like the other tabs in the calculator).
  5. Calculate the Radiation View Factor (F_{12}).

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Area of surface 2 (A_2) = 0.10 m²

Distance between the surfaces (d) = 1.0 m

Using F_{12} ≈ A_2 / (π d^2): F_{12} ≈ 0.10 / (π · 1.0²) ≈ 0.0318.