What an are is
One are equals one hundred square metres. It is a land area unit, used for plots rather than buildings.
Its use is common in Luxembourg in property listings, deeds and official statistics.
The conversion is immediate: a price per are divided by one hundred gives a price per square metre, and the reverse.
A plot of eight ares is eight hundred square metres, a common size for a detached house.
| Notion | Definition | Error to avoid |
|---|---|---|
| Are | One hundred square metres | Confusing are with square metre |
| Cadastral area | Area of the plot | Assuming it is fully developable |
| Developable area | What the regulation allows | Ignoring it in the comparison |
The three comparison traps
They produce errors by a factor of one hundred, which is never trivial. One are equals one hundred square metres.
Comparing without checking the unit. A listing, a statistic and a deed may use different units without this always being clearly stated.
Comparing a land price with a construction price. The first is often per are and covers a plot area; the second is per square metre and covers a living or built area. They are two quantities with no direct relationship.
Comparing areas that do not measure the same thing. Plot area, developable area, living area and built area are four distinct notions, and converting one to another depends on the applicable planning rules.
What a unit price does not tell you
Three limits, and they explain why two plots at the same price per are do not have the same value. They concern developability, shape and access.
It says nothing about developability. Two plots identical in area may permit very different built volumes under the applicable municipal rules.
It says nothing about shape. A narrow, sloping or awkwardly accessed plot carries a more expensive project at equal area.
It says nothing about the state of connection, covered in the article on serviced and unserviced land.
The price per are is therefore a market indicator, not a measure of value for a given project.
The relationship between plot and built area
A decisive technical point, often discovered too late. The developable area differs from the cadastral area.
It is not the plot area that determines what may be built, but the rules applying to that plot: permitted footprint, height, setbacks, density.
Those rules are municipal, and they vary between municipalities. They belong to the guide on municipal planning.
Consequence for estimating: relating land price to the achievable living area gives far more useful information than the price per are, but requires first knowing what is achievable.
How to compare usefully
Four steps, in this order.
Bring all figures to the same unit, before any other analysis.
Check what each area measures, plot or built area.
Establish the actual developable volume under the rules applying to the plot.
Calculate the land cost per achievable square metre of living area, the only quantity comparable between projects.
That last step is the one purchasers skip, and it is what reveals that a plot cheaper per are may cost more on the project.
What this means for a professional
Three rules.
State the unit used systematically in every document handed over, even where it seems locally obvious.
Never compare a land price with a construction price without making clear that the two quantities do not cover the same thing.
Relate land cost to the achievable square metre of living area when helping to choose between plots.
This article sets out principles of reading and serves professional orientation. It does not replace an estimate or consultation of the applicable planning documents.