In Belgium

Weighted area (surface ponderee / gewogen oppervlakte) is a more sophisticated surface measurement than habitable area. It applies correction coefficients to each room based on its characteristics, giving a more accurate picture of the dwelling’s actual usability.

The weighted area is used primarily in Brussels’ and Wallonia’s reference rent grids (grilles indicatives des loyers) to estimate fair rent levels based on the property’s characteristics.

How it works

Coefficients. Each room is measured and adjusted:

  • Full ceiling height (>2.50 m): coefficient 1.0
  • Reduced height (2.20-2.50 m): coefficient 0.75-0.90
  • No natural light: coefficient 0.50
  • Basement rooms: coefficient 0.50
  • Balconies/terraces: coefficient 0.25-0.50
  • Garages: coefficient 0.50

Example. An apartment with: living room 25 m2 (coeff. 1.0 = 25), bedroom 14 m2 (coeff. 1.0 = 14), kitchen 8 m2 (coeff. 1.0 = 8), bathroom 5 m2 (coeff. 1.0 = 5), attic room 12 m2 at 2.00 m height (coeff. 0.50 = 6), balcony 6 m2 (coeff. 0.25 = 1.5). Raw area: 70 m2. Weighted area: 59.5 m2.

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Good to know
The Brussels reference rent grid uses the weighted area to estimate indicative rents. A 60 m2 apartment with a large balcony and an attic room may have a lower weighted area (and therefore a lower indicative rent) than a compact 55 m2 apartment with all rooms at standard height.

Practical example

A tenant in Brussels wants to check if their rent is in line with the reference grid. Their apartment: 65 m2 raw area. After applying coefficients (low-ceiling storage room, windowless bathroom), the weighted area is 52 m2. The grid suggests 780-850 EUR/month for this weighted area and location. Their actual rent of 820 EUR is within the indicative range.