Ventilation & window sizing calculator

The room

Results update as you type. Nothing is sent anywhere — the calculation runs in your browser.

Floor area

144.0 sq ft / 13.38 sq m

Requirement applied

10% of floor area (habitable room)

Suggested window options

Each option reaches or exceeds the minimum. Openable percentages are stated so you can check them against the products you are pricing.

• 2 x Jalousie / louvre window — 3 ft x 4 ft

  21.60 sq ft openable

  2 units at 10.8 sq ft openable each — 21.6 sq ft total (12 sq ft nominal per unit, 90% openable).

  Assumption: Louvre blades open across the full sash; ~90% of the opening passes air.

• 3 x Casement window — 3 ft x 4 ft

  18.00 sq ft openable

  3 units at 6 sq ft openable each — 18 sq ft total (12 sq ft nominal per unit, 50% openable).

  Assumption: Two-sash casement with one operable leaf; ~50% openable.

• 4 x Awning window — 4 ft x 2 ft

  14.40 sq ft openable

  4 units at 3.6 sq ft openable each — 14.4 sq ft total (8 sq ft nominal per unit, 45% openable).

  Assumption: Top-hung awning sash at typical opening angle; ~45% effective.

• 1 x Fixed picture pane — 4 ft x 5 ft + 1 x louvre 3 ft x 4 ft + 1 x louvre 2 ft x 3 ft

  16.20 sq ft openable

  The fixed pane contributes 0 sq ft of ventilation; the louvres carry 16.2 sq ft openable. Use this where a view window or a structural opening rules out a fully operable elevation.

  Assumption: Fixed glazing counts as 0% openable; louvre panels at ~90% openable.

These are suggested combinations to meet the minimum standard. Real comfort depends on where the openings sit: air needs an inlet and an outlet on opposing or adjacent walls, not simply enough square footage on paper. See our cross-ventilation and passive cooling guide for the fuller explanation.

Results are for planning guidance only and should be confirmed against the specific local planning and building requirements applicable to your project before final design.