1. The first problem: the reference areas differ
Each sector of construction uses its own reference area, inherited from professional practice and the regulations specific to each use. These areas are not interchangeable and generate frequent misunderstandings in comparisons across types.
| Use | Usual reference area | Summary definition | Typical ratio to floor area |
|---|---|---|---|
| Apartments | Floor or habitable area | Internal area, or net habitable area | 0.80 – 0.87 habitable to floor |
| Houses | Floor or habitable area | Internal area, or habitable | 0.78 – 0.85 |
| Offices | Gross usable area | Net area after deducting the walls | 0.75 – 0.82 usable to floor |
| Retail and public buildings | Floor area, per the applicable regulation | Varies with the regime | 0.78 – 0.85 |
| Warehouses | Internal floor area | The internal envelope to the face of the walls | 0.88 – 0.93 |
| Hotels | Per room | Unit cost per finished room | Reasoned per room, not per m² |
| Care homes and serviced residences | Usable area | Private usable plus accessible collective usable | 0.72 – 0.80 |
| Swimming pools | Pool and hall usable area | Tank plus surrounds plus hall | Varies with the tank-to-building ratio |
Converting between the areas: the keys
Floor area is the statutory reference for planning permission. It includes walls, circulation and plant rooms, but excludes lift shafts and areas under 1.80 m in height.
Habitable area is the net area of a dwelling, without walls, partitions, steps or reveals. It is roughly floor area × 0.82 to 0.87 according to the programme.
Gross usable area is the floor area of an office plate after deducting the external walls and shafts. It is roughly floor area × 0.75 to 0.82.
To compare two ratios expressed in different units, bring them to the same base, generally floor area, before calculating the difference.
2. The matrix of comparability
Not every comparison is equally valid. Some are direct, using the same reference area and the same scope. Others require conversion. The table gives the method for each pair.
| Comparing… | …with | Direct comparison possible? | Normalisation method |
|---|---|---|---|
| Apartments, floor area | Offices, usable area | With care | Convert to a common floor area; multiply usable by 1.25 for the floor-area equivalent |
| Housing, floor area | Care home, usable area | With care | Convert usable to floor area by × 1.30, since usable is about 0.75 of floor |
| Ambient warehouse | Cold store | ✔ Direct | Same reference area, direct comparison valid |
| New apartments | Refurbishment | With care | Refurbishment is per m² of existing habitable, new build per m² of floor area; different coefficients |
| Hotel, per room | Student residence, per room | ✔ Direct | Same unit, but different room sizes, to be stated |
| Offices, usable | Coworking, usable | ✔ Direct | Same area, same use, direct comparison valid |
| Paris housing | Provincial housing | With a factor | Apply the regional factor before comparing; divide Paris by about 1.28 |
| New build | Roof extension | With care | Include land cost in the new build, strengthening cost in the extension |
3. The second problem: inclusions and exclusions vary
The second great bias is what the ratio includes or excludes. A ratio of 2,550 €/m² may cover everything, structure, finishing trades, equipment, internal external works, or only part. Before comparing two ratios, make sure they cover the same scope.
| Item | Included in the construction ratio? | When it is separate | Order of magnitude if separate |
|---|---|---|---|
| Standard foundations | Yes: strip footings or raft | Special foundations such as piles | + 5 to 25 % on difficult ground |
| Structure | Yes | Never separate | |
| Standard finishing trades | Yes | Premium finishes specified additionally | See specification levels |
| Technical equipment at standard level | Yes | Special equipment such as refrigeration or process plant | + 15 to 80 % according to speciality |
| Internal external works and services | Generally yes | External works outside the building footprint | + 5 to 15 % according to configuration |
| Land | Never | Always separate | Variable, 10 to 60 % of the total cost |
| Fees: design team, engineers, control | Never | Always separate | 12 to 18 % of the works excluding VAT |
| Furniture and mobile equipment | Never | Always separate | 5 to 20 % according to use |
| Basement parking | Often separate | To be added if the brief includes it | + 28,500 to 41,000 € per space |
| VAT | No, ratios exclude VAT | Always to be added at the applicable rate | 5.5 %, 10 % or 20 % according to programme |
The golden rule: every ratio published by Quostra excludes VAT, land, fees, separate basement parking and tax. To rebuild the complete cost of an operation those items must be added, and they can represent a further 30 to 60 % according to location and legal structure.
4. The third problem: the specification level
An office ratio can run from 1,840 €/m² of usable area for a minimal category A shell to 4,590 €/m² for a premium corporate fit-out. An apartment ratio can run from 1,630 €/m² of floor area for functional social housing to 3,570 €/m² for premium. Comparing two ratios without stating their specification level is like comparing a small hatchback with a sports car by looking only at price per kilogram.
- For housing: state whether the ratio is social, intermediate or premium private. The gap between the extremes is 50 to 80 %.
- For offices: state the delivery level, category A, enhanced A, fitted out. The gap between category A and premium fitted is 80 to 150 %.
- For public buildings: state whether the ratio includes the special equipment, professional kitchen, pool, sports equipment, or only the bare building.
5. The five-step method for a valid comparison
Step 1: identify each ratio's reference area
Systematically check the unit behind every published ratio: per square metre of floor, habitable, usable or internal area, per room, per bed. It is the first question to ask before any comparison.
Step 2: convert to a common area
Choose a common area, generally floor area, as the universal statutory base, and convert each ratio using the conversion coefficients. For example, an office ratio in usable area × (1 / 0.78) gives the floor-area equivalent.
Step 3: check the scopes match
Check that both ratios include the same items: standard foundations, finishing trades, technical equipment, internal external works. If one includes parking and the other does not, deduct or add it before comparing.
Step 4: normalise the specification level
Make sure you are comparing comparable specification levels. Social housing is not comparable with premium housing without correction; the specification gap represents 30 to 50 % of the ratio. For offices, state category A, enhanced A or fitted.
Step 5: apply the regional factor
If the two programmes are not in the same area, bring both ratios to the same geographic base, standard provincial at 1.00, before comparing. Housing in Paris at 2,600 €/m² is not dearer than housing in Nantes at 2,000 €/m²; it is the same price once the factor is applied, since 2,600 / 1.30 = 2,000 €.
6. A worked example: apartments against offices
Take two illustrative programmes:
- Programme A: apartments in Nantes, published ratio 2,100 €/m² of floor area, standard specification, excluding parking.
- Programme B: offices in Lyon, published ratio 2,400 €/m² of usable area, enhanced category A, excluding parking.
Applying the method: (1) the areas differ, floor against usable; (2) convert the office ratio to floor area: 2,400 × (1 / 0.78) = 3,077 €/m²; (3) the scopes match, both exclude parking; (4) specification: standard housing is roughly equivalent to enhanced category A on the finishing trades, so the comparison is acceptable; (5) regional factors, Nantes 1.00 and Lyon 1.08, so the Lyon ratio brought to provincial base is 3,077 / 1.08 = 2,849 €/m² of floor area.
Normalised conclusion: enhanced category A offices in Lyon come to 2,849 €/m² of floor area on a standard provincial base, against 2,100 €/m² for housing, that is 36 % more. That is the honest comparison, very different from the raw one, 2,400 against 2,100 or +14 %, which under-stated the real gap.
You have better things to do. Submit your project on quostra.com; a normalised estimate with a cross-type comparison method within 72 working hours.
In summary
Comparing two construction ratios without care leads systematically to wrong decisions. The three biases to neutralise are the reference area, floor, habitable, usable, internal, per room, all different, the scope of inclusion, since land, fees and parking are often excluded, and the specification level, where the gap runs from 50 to 80 %. The five-step method, identify, convert, check the scope, normalise the level, apply the regional factor, produces economically valid comparisons. In the Lyon offices against Nantes housing example, the raw comparison gives +14 % and the normalised one +36 %: that is the order of magnitude of the error when no method is applied.
Reference basis of the figures
These bands are orders of magnitude for framing, and their reference market is the Paris region. They serve to place a budget at the earliest stages and to compare building types with one another. They replace neither a tender exercise nor an estimate prepared on drawings, and they are not a record of prices actually charged.
The ratios per square metre and per item on this page are stated in January 2026 values. They were updated from January 2025 values, the basis adopted for the whole cocoon, using the BT01 all-trades index published monthly by INSEE on its 2010 base: 132.0 in January 2025, 134.7 in January 2026, a rise of about 2 %.
The global amounts quoted as examples, and any rents, charges or receipts expressed per year or per night, remain on their own basis: a building cost index does not apply to them.
To bring the ratios forward, apply the usual revision formula: updated value = page value × (BT01 for the month in question / 134.7). The index has kept rising since: it stood at 138,3 in June 2026, the last value published when this page was checked, that is 2,7 % above the reference base. BT01 measures contractors' input costs, wages and social charges, materials, plant and energy, not the prices actually tendered.
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Sources: the BT construction cost indices published monthly by INSEE on its 2010 base, used to update the figures · construction cost statistics from SDES, the statistical service of the ministry responsible for construction · regulatory texts published in the Journal officiel and consolidated on Légifrance for the requirements cited.