How millesimi are calculated: surface and coefficients

Thousandths (millesimi) express the proportional value of each unit relative to the whole building, set in thousandths out of a total of one thousand. The calculation does not coincide with simple cadastral floor area: you start from the real surface and correct it with a set of coefficients that account for the features affecting the use and market value of the property. The result is the virtual surface, from which, by proportion, the thousandths are derived. Understanding this step helps administrators and owners read and check the tables.

From real surface to virtual surface

The starting point is the usable surface of each unit, measured in a uniform way for all the properties in the condominium. To this surface you apply multiplying coefficients, usually values close to one, which increase or reduce the weight of the unit based on specific features. Multiplying the real surface by the coefficients gives the virtual surface, that is a weighted surface that makes units with different features comparable.

The most common coefficients

There is no statutory schedule of coefficients: the choice and the amount are up to the drafting professional, who applies them consistently and with documentation to all units. The coefficients most widespread in appraisal practice consider the elements that affect the use value of the unit within the building.

• Floor or floor height coefficient: values higher or lower floors depending on the context.
• Exposure and orientation coefficient: north, south, east, west affect comfort and light.
• Brightness and frontage coefficient: open or internal outlook, presence of natural light.
• Use coefficient: home, office, shop, cellar and garage carry different weights.
• Functionality or internal layout coefficient, where relevant.

Calculating the general thousandths

Once the virtual surface of each unit is determined, you add up all the virtual surfaces of the building. The thousandths of each unit are obtained by dividing its virtual surface by the total and multiplying by one thousand. The sum of all shares must equal exactly one thousand: this balancing check flags any calculation or rounding errors. This is the general ownership table, the basis for the conservation and enjoyment of undivided common parts.

Special or use tables

Alongside the general table, the condominium prepares specific tables for expenses subject to use criteria, such as stairs, lift and heating. These tables do not necessarily use the same coefficients as the general one: the stairs table, for example, weights floor height following the logic of Article 1124 of the Civil Code, while the heating table can be based on volumes or consumption. Each table distributes one thousand thousandths according to the parameter relevant to that service.

Who drafts the tables and with what status

Drafting the tables requires appraisal expertise and is usually entrusted to a professional, who produces a report with the criteria adopted and the coefficients applied. The tables do not grant real property rights and are not contractual, as clarified by the Joint Chambers of the Court of Cassation in judgment no. 18477 of 2010: they measure values and allocate expenses. For this very reason they can be approved and corrected under the rules for meeting resolutions, except for the rectification and revision cases of Article 69 of the implementing provisions.

Why transparency of the calculation matters

A well made table is verifiable: every owner must be able to trace the assigned thousandths back to the surface and the coefficients used. Transparency reduces disputes and makes it easier to spot errors when the conditions of the building change. Keeping the technical report, the surfaces and the coefficients in an orderly way is therefore an integral part of good administration, not a formal detail.

Moving from virtual surface to thousandths and keeping the general and use tables consistent is work that automation makes reliable. AmministraPro lets you record units with their thousandths, manage multiple tables and see the immediate impact of each change on the split, with the balancing always under control. The accounting and table features are described on /funzioni and the plans on /prezzi.