Size a louvre from airflow, free-area velocity, free-area ratio, safety margin, and aspect ratio, or reverse-calculate airflow and actual velocity.

Apply the entered airflow allowance, then round both dimensions upward. The resulting aspect ratio may change.

Preliminary geometric sizing. Use the manufacturer’s free-area percentage for the exact model, dimensions and screen. Confirm tested pressure drop and rain performance before selection.

Sizing requires a positive design velocity. Use manufacturer performance data for the selected application.

Selects the output dimension unit. A rounding increment is required; this does not select an available product size.

Airflow allowance and rated onset comparison

Blank means no additional airflow allowance; no universal safety factor is assumed.

Blank or 0 omits this arithmetic comparison. Use the same free-area basis and test configuration; it does not certify rain protection.

Related Calculators

Louvre Size Formula

The formula below gives gross rectangular face area from known dimensions. For airflow sizing, required gross area = adjusted airflow / (free-area velocity × free-area fraction), using consistent units.

S = W × H

Variables:

  • S is the louvre size
  • W is the louvre width
  • H is the louvre height

Gross face area equals width × height. Net free area excludes blades, frame and supports and equals gross area × the manufacturer’s free-area fraction for that exact size and configuration. The calculator applies an entered airflow allowance, derives dimensions from the aspect ratio, and rounds each upward. Verify the actual rounded product’s free area and tested performance.

What is a Louvre?

A louvre is a structure consisting of a series of horizontal slats angled to admit light and air with rain rejection, sun control or acoustic performance depending on the design and its tested ratings. Louvres are commonly used in windows, doors, and other openings to allow ventilation while providing privacy and protection from the elements. They can be made from various materials, including wood, metal, and glass, and are often used in architectural designs for both functional and aesthetic purposes.

How to Calculate Louvre Size?

The following steps outline how to calculate the Louvre Size.

  1. First, determine the width of the louvre (W).
  2. Next, determine the height of the louvre (H).
  3. Finally, calculate the louvre size using the formula S = W * H.
  4. After inserting the values and calculating the result, check your answer with the calculator above.

Example Problem : 

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

Louvre Width (W) = 5 units

Louvre Height (H) = 3 units