Square Footage and Surface Area: The Hidden Variables

The calculation of property surface areas in Monaco has long been a topic of debate. Unlike in France, there is no formal legislation governing these calculations, leading to varied practices and sometimes vague terminology.


How Are Surfaces Calculated?

Without the systematic involvement of a certified surveyor, measurement methods can vary significantly. In the residential market, total surface area or saleable area typically includes:

•  Interior spaces (including walls)

•  Outdoor spaces (balconies, terraces, gardens)

•  Half of shared walls

However, in many cases, the reported figure only accounts for the interior space and outdoor areas, as detailed floor plans including wall thicknesses are often unavailable. This can lead to notable discrepancies, particularly in duplexes or penthouses, where the advertised size may significantly exceed the actual usable living space.


Weighting Factors: A Step Toward Standardization

The Monaco Real Estate Chamber (CIM) has proposed a set of weighting factors to provide a more accurate reflection of outdoor space value:

•  100% of the area, if it represents less than 30% of the interior surface 100%

•  50% of any outdoor space exceeding that threshold 

•  50% for rooftop terraces and gardens

Not all agencies in Monaco are CIM members, meaning these guidelines are not universally followed.Additionally, other factors influence property valuation, such as condition, orientation, accessibility, and view. Given the uncertainty surrounding wall thicknesses, a standard 10% coefficient is often applied to interior measurements to account for structural walls.


An Ambiguous Legal Framework

According to Monaco’s Law n^o1.391 (amended by Law n^o1.531), the building structure is considered a common area in co-ownership properties. Yet, it is still included in the calculation of saleable surface area. This contradiction raises several concerns:

•  How are co-ownership fees allocated if common areas are sold as private property?

•  How does the inclusion of structural elements affect price-per-square-meter calculations when these spaces cannot be used?

These inconsistencies complicate real estate appraisals and comparative market analyses, especially since Monaco’s sales deeds do not always specify surface areas.


Impact on Advertised Prices

Consider this scenario:

•  A property is listed at €50 000 per sqm based on 110 sqm (using the Monaco method). 

•  If a more conventional calculation is applied (excluding walls and applying a 10% adjustment), the actual living space decreases, and the effective price rises to €55 000 per sqm.

•  International comparative studies struggle to accurately reflect Monaco’s market.

•  The displayed price per square meter may not always represent the real value of usable space.

A Need for Standardized Measurements

If Monaco were to align its measurement standards with France, two scenarios could emerge:

1. Reduce reported surface areas by 10%, impacting property valuations.

2. Maintain current measurements while adjusting price-per-square-meter calculations, artificially inflating advertised prices.

Additionally, the DPUM (Monaco’s Urban Planning Department) bases its assessments on volume rather than surface area, which can impact residency applications, particularly for studios.
According to IMSEE, Monaco’s statistics office, 86% of sold property surfaces in 2024 were documented. However, their methodology differs:

•  Balconies, loggias, and terraces are counted in full

•  Gardens and rooftop terraces are weighted at 50%

Conclusion

As of today, there is no single, legally binding method for calculating property surface areas in Monaco. The only exception is the density surcharge tax, where the government applies a method closer to French standards. For any property acquisition, it is essential to ask the right questions:

•  What surfaces are actually included in the calculation?

•  How were they measured?

Ultimately, a certified surveyor remains the only way to ensure a precise and legally defensible measurement.