Carrez Law Floor Area Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/9/2026
Carrez law floor area is calculated by deducting walls and partitions, stairs and shafts, door and window recesses, and any part with a ceiling height below 1.80 m from the gross floor area. For a 55 m² gross apartment with converted attic space, the Carrez area can drop to 46.5 m².
Explanation
France's Carrez law (law n°96-1107 of December 18, 1996) requires that any deed of sale for a co-owned unit state its exact private floor area, precisely defined by implementing decree n°97-532 of May 23, 1997: the floor area of enclosed and covered rooms, after deducting the surface occupied by walls, partitions, stairs and stairwells, technical shafts, and door and window recesses. The most commonly misunderstood rule concerns ceiling height: any part of the home where it's below 1.80 m is simply excluded from the calculation, regardless of its actual use — which is why converted attics, low mezzanines, or sloped ceiling areas often noticeably reduce the Carrez area compared to the gross floor space actually used day to day. This rule also explains why a duplex apartment with an attic can show a Carrez area markedly smaller than its perceived living space, which frequently surprises buyers who tour the property before consulting the official assessment. The financial stakes of this calculation are real and directly enforceable in court: a measurement error exceeding 5% to the buyer's disadvantage entitles them to a proportional reduction in the sale price, through legal action brought within one year of signing the final deed — which is why the official measurement must always be carried out by a certified property surveyor, never estimated on your own for the purposes of a deed of sale. This calculator gives a useful ballpark estimate for planning ahead of a viewing or checking the consistency of an assessment already carried out, but never replaces this mandatory professional measurement; to estimate the overall cost of the purchase once the area is known, see our notary fees calculator. The attic and sloped-ceiling spaces excluded by the 1.80 m rule remain real volumes of the home nonetheless, often insulated separately from the rest — see our insulation thermal resistance calculator to assess the thermal performance of these spaces.
Example: an apartment with converted attic space
Inputs
Gross floor area: 55 m². Walls and partitions: 3 m². Stairs and shafts: 1 m². Recesses: 0.5 m². Area under 1.80 m: 4 m².
Calculation
Carrez area = 55 − 3 − 1 − 0.5 − 4 = 46.5 m².
Result
This apartment's estimated private floor area under the Carrez law is 46.5 m², noticeably less than the 55 m² gross floor area measured.
Frequently asked questions
Does this estimate replace the mandatory official assessment when selling?
No, absolutely not: the Carrez law requires that the private floor area stated in the deed of sale be measured by a professional (certified property surveyor), with the tools and methodological rigor required. This calculator only gives a useful ballpark estimate ahead of a viewing or to check an assessment's consistency, but has no legal or contractual value.
Do a terrace, balcony, or garage count toward the Carrez area?
No: the Carrez law only applies to enclosed and covered rooms. Terraces, balconies, loggias, parking spaces, cellars, and garages are excluded by definition, even if they're part of the same co-owned unit — they can be mentioned separately in the listing or deed of sale, but never added to the Carrez area itself.
What happens if the actual area differs by more than 5% from what's stated in the deed?
If the error is to the buyer's disadvantage (actual area more than 5% below what was stated), they can request a proportional reduction in the sale price in court, provided they act within one year of signing the final deed. Past that deadline, or if the gap is under 5%, no recourse is possible on this basis alone.