How to Calculate the Floor Area of a Home

How to calculate the floor area of a home is a question many owners ask themselves when selling, valuing or renovating a property. The habitable surface - often referred to as ‘living area’ - forms the basis for the price per m², EPC calculations and sales brochures. In Belgium, this is not measured as total floor area, but as usable spaces according to common conventions. An incorrect calculation can lead to disputes with buyers or an underestimated sale value. This article explains step by step how to do it correctly, taking into account both region-specific and general Belgian practices.

What counts as habitable surface area?

First, let's define what is included. The habitable surface covers all spaces that can effectively be used for living, sleeping, cooking or relaxing. These are:

• living room, bedrooms, kitchen, bathroom;
• converted loft, study, dining room;
• entrance hall, corridors, built-in cupboards (if usable).

Do not include:

• garage, cellar, unconverted loft;
• utility rooms, unheated spaces;
• staircases, roofs, exterior walls.

For sloped ceilings, you measure from the point where the standing height is at least 1.5 m. This prevents inflated figures and follows market convention.

How to calculate the floor area step by step

The basic formula is simple: length × width per room, then add them up. For irregular shapes, split the space into rectangles. Here is the practical approach:

Step 1: draw a sketch or use a floor plan

Draw a floor plan for each storey. Do you have an architect's plan? Perfect - measure the interior dimensions from it. No plan? Use a laser distance meter or tape measure for accuracy.

Step 2: measure each room

Measure length and width at floor level:

• Rectangular room 5 m × 4 m = 20 m².
• L-shaped room: split into two rectangles (e.g. 5×3 m = 15 m² + 2×4 m = 8 m² = 23 m²).

Round to the nearest whole or half m² for readability.​

Step 3: adjust for sloped walls and recesses

For loft spaces: only measure where the height is ≥1.5 m. Sloped sections are ignored or calculated proportionally. For round or complex shapes, use software such as CADGIS or dedicated apps.

Step 4: add up and classify

Total all qualifying spaces:

Don't forget to add any converted rooms.​

Step 5: check and document

Double-check using online tools (cadastral plan via CADGIS for plot and garden). Keep your measurements on file for the sale.

Differences by region and application

In Flanders, the market follows the standard convention: usable spaces from 1.5 m height. For the EPC certificate or the information sheet: strict rules apply (garage excluded). In Wallonia and Brussels, the approach is similar, but it is worth checking locally.

When selling, accuracy is crucial: buyers compare prices per m². Incorrect information can lead to claims for misrepresentation. For a mortgage or a grant, specific definitions apply (e.g. habitable surface vs. total area).

Avoiding common mistakes

• Counting too much: exclude the garage or unheated loft.​
• Measuring inaccurately: use a laser for precision.​
• Not adjusting for sloped roofs: measure from 1.5 m.​
• Forgetting to add up: use a table.​

Digital tools for quick calculations

• CADGIS/Myloopings: measure plot and garden online.​
• Apps such as RoomScan: scan and calculate automatically.
• Architecture software: for complex shapes.​

Why getting the floor area right pays off

An accurate calculation of the floor area maximises your sale value: a realistic price per m² attracts serious buyers. In your sales communication, being transparent builds trust.

For renovation: base your material purchases (flooring, paint) on exact m² figures.​

Want to know what your home is worth with a correctly calculated floor area? Request a free valuation. A real estate agent will refine your calculation and put it in the context of market prices per m².