The price per square metre is the most quoted and least reliable figure in the property market. It has one merit: it is simple. It has three flaws, and each is enough to skew a valuation.
Flaw 1: price is not proportional to floor area
Intuition says a property twice as large is worth twice as much. The market says otherwise. Part of a home's value — the land, the location, the kitchen, the bathroom, the connections — does not double when the floor area doubles.
The result: the price per m² falls as the area grows. A 40 m² studio shows a markedly higher price per m² than a 200 m² house on the same street, without that saying anything about the quality of either. Applying the municipality's price per m² to a large property overvalues it; applied to a small one, it undervalues it.
Flaw 2: the average aggregates incomparable properties
A municipal price per m² is calculated across all sales: studios and villas, new build and renovation projects, dark ground floors and top floors with a view. That is not the price of a property, it is the average of a heterogeneous population.
Two municipalities showing the same price per m² can have very different markets: one with many small flats expensive per metre, the other with family houses cheaper per metre but dearer per unit.
Flaw 3: the denominator itself is vague
« Habitable floor area » has no single definition in Belgium. Depending on practice, converted attics, the conservatory, the integrated garage, cellars or areas under 1.80 m in height may or may not count. Two listings for the same home can show 120 and 145 m².
Dividing a reliable price by an uncertain area does not produce a reliable ratio: it produces a ratio you cannot interpret.
What price per m² does well
It remains useful for comparing properties of the same kind within the same area: two flats of similar size, in the same neighbourhood, in the same condition. There the denominator is comparable and non-linearity barely comes into play.
It is also readable over time: tracking the price per m² of a homogeneous segment year after year says something true about the trend.
What to look at instead
A range, not a point. The gap between the first and third quartile of sales describes the market far better than a single value: it says both where the centre lies and how widely properties scatter around it.
Transaction volume. A median calculated on 400 annual sales and a median calculated on 9 sales do not read the same way. Volume conditions how much confidence the figure deserves.
Geographic granularity. Location explains a considerable share of price dispersion. Measured on Belgian statistical sectors, that dispersion drops clearly when moving from municipality to neighbourhood: the interquartile spread for houses falls from around 55 % of the median at municipal level to around 46 % at sector level (Source: Statbel, statistical sectors 2022-2024). In other words, close to a third of what « varies » within a municipality is not the property — it is the location.
The property's characteristics. Floor area, condition, energy performance, number of façades, outdoor space: each shifts the price, and each reduces uncertainty once known. That is what distinguishes a valuation from an average.