Indicative onlyThese tools provide indicative calculations only. No warranty is given as to the accuracy, completeness or fitness for purpose of any output. Using this site does not create a professional relationship or duty of care between brickdims and the user. Results must not be used as a substitute for professional advice, site-specific assessment, or formal compliance sign-off. Building regulations are subject to change, so always verify against the current editions of the relevant Approved Documents and consult a building control officer where required. brickdims accepts no liability for any loss, damage or non-compliance arising from reliance on these tools, to the fullest extent permitted by law. If any part of these terms is found unenforceable, the remaining terms continue to apply. These terms are governed by the laws of England and Wales. By using this site you accept these terms.
Free area calculator
BETA
Calculate the free area of a louvre from its face dimensions and free area percentage.
Results from brickdims.com tools are indicative only. Using this site does not create a professional relationship or duty of care. Not a substitute for professional advice or formal compliance sign-off.
Louvre
Results
Face area
1 m²
Free area
0.5 m²
50% of the face area
FAQs
What is louvre free area?
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Free area is the open area that air can pass through, given as a percentage of the louvre's face area. The blades and frame take up the rest.
How do I calculate free area?
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Multiply the face area by the free area percentage. A 1000 × 1000mm louvre at 50% free area has 0.5m² of free area.
What free area do louvres usually have?
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It varies widely with the blade profile, and weather louvres with better rain defence usually have less. Always use the manufacturer's tested figure rather than an assumed one.
Is free area the same as effective area?
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No. Free area is the geometric opening. The air a louvre actually passes is lower because of resistance through the blades, which manufacturers express as a coefficient of discharge or an effective area.
How much free area does a substation need?
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It is set by the network operator's specification for the transformer size, so check the DNO's requirements for the project before sizing the louvres.