The computo metrico estimativo: from preparation to price books and specification

The computo metrico is the ordered schedule of the operations a design requires, stating for each the unit of measurement and the quantity. It answers one question: how much of it is being done.

The computo metrico estimativo is the same schedule with the unit rate and resulting amount added for each item. It answers a second question: what it costs.

In everyday usage the two expressions are treated as synonyms, and in most cases someone saying computo metrico means the priced document. The distinction nonetheless exists and has practical consequences. Moving from the first document to the second adds no information about the design: it adds an economic valuation drawn from a source external to the design, namely the prezzario. It follows that quantities do not age while rates do, and that an unpriced bill prepared two years earlier remains valid if the design has not changed, whereas a priced bill needs revaluing.

This distinction, the cases where only the unpriced document is needed and how one moves from one to the other are the subject of dedicated coverage within this guide. It also carries the criterion for choosing between the two.

One further point should be made, because it prevents the most common misunderstanding with clients. The priced bill is an estimate of the cost of the works according to a stated source, not the price that will be paid. The contract price arises from the accepted offer, and may depart from the estimate in either direction without either figure being wrong.

The Italian public contracts code enacted by Legislative Decree 36 of 2023 reduced the number of design stages from three to two. The intermediate stage was abolished and the sequence now runs from the progetto di fattibilità tecnica ed economica, the technical and economic feasibility design, to the progetto esecutivo, the detailed design.

The simplification did not lighten the workload. Design obligations previously spread across three steps now sit on two, and the detailed design absorbs part of the detail that used to mature gradually. The effect on estimating is direct: the bill accompanying the detailed design must be complete and final, because there is no longer an intermediate stage in which to correct roughly estimated quantities along the way.

Article 22 of Annex I.7 to the code lists the documents making up the detailed design, and the bill of quantities appears together with the quadro economico, the project cost framework. Alongside them sit deliverables that directly condition its content.

Deliverable	Relationship with the bill
Drawings	Source of the quantities. Every item must be traceable to a drawing
Schedule of unit rates and any analyses	Holds the rates applied and the analyses for items absent from the price books
Capitolato speciale d'appalto	Sets the technical requirements justifying the choice of each item
Labour incidence schedule	Derives from the bill and makes the labour component legible
Cronoprogramma	Places the measured operations in sequence over time
Health and safety plan	Determines the safety charges, treated separately in the bill
Quadro economico	Places the works amount within the total cost of the project

The bill is therefore a synthesis deliverable translating into quantities and value choices made elsewhere. It cannot be produced in isolation nor deferred to a stage after design. Its role within the detailed design, the designer's responsibility and the question of its contractual value are examined in The computo metrico estimativo in the progetto esecutivo.

The quality of the outcome depends almost entirely on the order in which you proceed. The route runs through seven stages.

Define the structure. The first decision concerns the layout rather than the quantities: by work category following the logical sequence of construction and, within each, by building element or by floor. This structure determines the readability of the summaries, the ability to apportion work stage percentages under a lump sum contract, and the ease with which the works supervisor will locate items during valuation.

Take off the quantities. Every quantity must be derived from the drawings through an explicit calculation, written out line by line with dimensions and the number of elements. An explicit calculation is verifiable, can be updated when the design changes and is defensible at verification. Deductions must be set out line by line rather than absorbed into the total.

Apply the unit rates. Each item must be located in the prezzario by reading its full description rather than its heading, checking that the unit of measurement matches the take off, that the territorial scope corresponds to the location of the works, and that work excluded from the description is measured elsewhere.

Determine the missing items. Where an item is absent, or where an existing item does not match the real conditions, the rate is determined by analysis.

Isolate the safety charges. These derive from the health and safety plan and must be kept separate from the measured work, with the separation built into the structure from the first stage.

Build the summaries. The summary by work category, the labour incidence schedule and the works amount to be carried into the cost framework all derive from the bill. They should be produced together, and if they do not reconcile the error is in the bill.

Verify. The final step is a cross check running back up the documentary chain: completeness against the specification, traceability of the quantities, consistency of units, absence of double counting, plausibility of the percentage incidences, separation of safety charges.

The full procedure, with a worked example on a single item and guidance on setting up the working file, is in How to prepare a computo metrico estimativo step by step. It also carries the three checks to run on every item.

One point deserves isolating because it is the principal source of invisible errors. Two surveyors measuring the same wall can arrive at different quantities without either being wrong, because a quantity is not a physical fact but the result of applying a convention, and the convention is set by the prezzario.

Every price book contains a section devoted to measurement criteria and technical specifications, establishing for each category the unit in which measurement is taken, what the rate covers, which deductions apply and which additions are permitted. It is consistently the least read and the most decisive part: applying the correct item with the wrong basis produces an error that no check on the total will reveal, because the bill stays internally consistent and what breaks is its correspondence with the site.

The emblematic case is measuring vuoto per pieno, literally void as solid, which means measuring a surface as though the openings were not there. It is not a shortcut: it reflects the fact that for some operations the presence of an opening does not reduce the effort in proportion to the area removed, and sometimes increases it, because reveals, heads and sills have to be worked. The dimensional thresholds and the treatment of surrounds vary from one price book to another and there is no single national convention: they must be read in the price book adopted.

The units of measurement, the treatment of the main work categories and the method for checking criteria on a bill received are the subject of dedicated coverage. It also covers the treatment of openings and overlaps.

On the tools side, extracting quantities from an information model introduces a specific and frequently underestimated problem. The model groups by construction element, the prezzario by operation, and the geometric area the model returns does not coincide with the quantity the measurement convention requires. An element modelled as a single object corresponds to several prezzario items, each with its own basis, and the correspondence needs defining before modelling rather than reconstructing afterwards.

In public works the choice of price source is not a professional preference. Article 41 paragraph 13 of the code provides that for works contracts the cost of products, equipment and operations is determined by reference to prices current at the date of design approval, taken from the price books updated annually by the territorially competent regions and autonomous provinces. Only in cases expressly authorised by the Ministry of Infrastructure and Transport may recourse be had to prezzari speciali adopted by contracting authorities.

Article 31 of Annex I.7 sets out the hierarchy to follow where an item has to be determined by analysis, and the same hierarchy guides the choice of primary source. The same hierarchy guides the choice of source to cite.

Order	Source
1	Price books of the territorially competent regions and autonomous provinces
2	Prezzari speciali of the contracting authority, with ministerial authorisation
3	Official lists and lists of the local chambers of commerce
4	Current market prices for the location of the works

Two elements need bearing in mind. The first is the time criterion: rates must be those current at the date of design approval. The second is annual validity: price books cease to have effect by 31 December each year and may be used transitionally until 30 June of the following year for tender designs approved by that date. The expected approval date therefore has to be considered before valuation begins, not afterwards.

The statutory basis, the timetable by which price books are prepared, the territorial rule, the transitional regime and the move from one edition to the next are examined in Regional prezzari: which one to use and how. The overall picture of the sources, including those usable in private construction and their limits, is in Price books for the computo metrico estimativo.

The framework is in transition. The 2026 budget law provided for a national price book with a supporting and coordinating function in relation to the regional books, without replacing them, indicating price variation thresholds applicable at territorial level. The mechanism depends on an implementing decree whose procedure has not been completed, and the operational reference therefore remains the regional prezzario. The state of the procedure is set out in dedicated coverage, which should be consulted before treating the mechanism as operational.

No prezzario covers the entire field of possible operations, and no project consists solely of standard work. Price analysis is the instrument assigning a value to items the list does not contain.

The method is codified by article 31 of Annex I.7 in three steps. The corresponding elementary prices are applied to the estimated quantities of materials, labour, plant hire and transport needed to produce one unit of each item, giving the technical cost. A percentage varying between 13 and 17 per cent is added for overheads, according to the importance, nature and duration of the project and any particular requirements. A percentage of 10 per cent is finally added for the contractor's profit.

The order of the last two steps is not immaterial: profit is calculated on the technical cost already increased by overheads, and applying the two rates separately to the same base understates the rate by several percentage points on every item analysed. Applying both rates to the same base produces a divergence on every item.

The analysis must be produced as a deliverable and attached, because it is what makes the rate verifiable at design verification and contestable on technical grounds during construction. The full method, the construction of unit inputs and the recurring errors are examined in the articles of the price books branch referred to above.

Where the need emerges during construction the determination follows a formal procedure, involving the works supervisor, the single project officer and the contractor, and concluding with the signature of a record. That signature is the moment the new rate becomes binding, and the moment at which a contractor not in agreement must enter its reservation, failing which it lapses.

Some deliverables of the detailed design serve a descriptive purpose, others a contractual one. The bill sits at the boundary between the two, and its robustness depends on consistency with the documents beside it.

The capitolato speciale d'appalto sets the technical and administrative rules of execution. Article 32 of Annex I.7 requires it to be divided into two parts, one containing the description of the works, the other the specification of technical requirements. The link with the bill runs both ways: every measured item must find in the specification the description of the work justifying it, and every onerous requirement must find in the bill an item valuing it. Discrepancies between the two documents are the leading source of requests for new rates during construction. Its structure, typical contents and the capitolato informativo introduced by the corrective decree are in The capitolato speciale d'appalto: structure and contents.

The schedule of unit rates collects the rates applied in the bill, including items determined by analysis, without quantities. It is the document that outlives the tender and becomes the operational instrument of the whole construction stage, because variations are valued by applying the rates in the schedule attached to the contract reduced by the discount percentage offered. A counterintuitive drafting rule follows: it is worth including items of modest economic weight but likely quantity variation, because their value lies not in the amount they represent in the design but in the cover they provide during construction. Connected to the same deliverable is the labour incidence schedule, which aggregates in tabular form the labour component attributable to the parts of the works and makes the estimate of that component verifiable.

The form of consideration determines the very function of the bill. Under an appalto a misura, a measured contract, the consideration is determined by applying the unit rates to the quantities actually executed, and quantity is a variable. Under an appalto a corpo, a lump sum contract, the consideration is fixed for the completed works, quantity is not a variable, and the bill serves to build the contract amount and to apportion the work stage percentages governing interim payments. The substantive difference is where quantity risk sits. The implication for whoever prepares the estimate is stark: a lump sum contract calls for a higher level of certainty about quantities than is acceptable under a measured contract, because the error cannot be recovered in the valuation.

The overall picture of the contract deliverables and the cross checking sequence is in The contract documents of the progetto esecutivo. It also carries the discrepancies that recur most often between deliverables.

The total of a bill is not the amount put out to tender, and neither is the total cost of the works. Precise steps sit between the three figures.

From the bill the works amount is built by distinguishing two components treated differently: the amount of work subject to discount, on which operators submit their offer, and the safety charges, which derive from the health and safety plan and are not subject to discount. To this is added the obligation, under article 41 paragraph 14, to quantify and state labour costs separately in the tender documents.

A distinction here generates frequent errors. The labour costs estimated under article 41 paragraph 13 relate solely to those costs and may not incorporate any other element, whereas the price analyses used to determine the tender amount also include overheads and profit. The two figures coexist in the same document and are not interchangeable. To this is added a second distinction, between the safety charges deriving from the plan, which belong to the design, and the contractor's own safety costs, which belong to the bid.

The quadro economico places the works amount within the total cost of the project by adding the sums at the contracting authority's disposal. Established practice sets it out in four columns, separating amounts prior to the tender from those following it: the pre tender column is completed from the figures deriving from the bill, the post tender column is populated progressively according to the awards made and the costs incurred. A framework updated by overwriting loses the record of the forecast and makes divergence impossible to measure, which is the document's principal usefulness. The four column structure is therefore a control instrument and not a formal convention.

The sums at disposal cover professional fees, taxes, utility connections, any land acquisition, contingencies and provisions. On an ordinary building project the works amount represents a share in the region of two thirds to three quarters of the total cost, and understatement of this section is common because its items are estimated with the least analysis. The contingency provision deserves particular attention, because the law provides for its use, up to a limit of fifty per cent, to meet the additional costs of price revision: it is therefore not a free reserve. Savings arising from the tender discount, for their part, are not definitively released at the point of award: they remain tied to the project until it concludes.

The route through the three levels of amount is set out in From the bill of quantities to the tender amount. It also covers the treatment of the non discountable component.

The bill belongs to the design stage. The contabilità dei lavori, works accounting, belongs to the construction stage and establishes what has actually been built. Confusing the two is a recurring error, and the distinction must be held firmly because the documents, the responsible parties and the legal effects all differ.

Annex II.14 to the code places on the works supervisor the control of expenditure through the accurate and timely completion of the accounting documents, which are public instruments for all legal purposes. Article 12 identifies the site diary, the measurement book, the accounting register and its summary, the interim valuation, the payment certificate and the final account.

The sequence is rigid. The works supervisor measures the work executed and records it in the measurement book, the measurements are valued in the accounting register at contract rates, from the register the interim valuation is derived, summarising everything executed since the start of the contract and stating the consideration accrued, the instalments already paid and by difference the instalment now due. The works supervisor transmits the interim valuation immediately to the single project officer, who issues the payment certificate having verified the contractor's social security compliance.

The most exposed document is the interim valuation, because it is where site accounting meets cash. It is covered, with a worked calculation and the checks to run before issue, in Interim valuations and the payment certificate.

The records preceding it warrant attention in their own right, because it is in the measurement book that establishment materially takes place and in the accounting register that the contractor's signature is taken, with the regime governing reservations that follows from it. Reservations must be entered, failing which they lapse, on the signature immediately following the prejudicial event, and those not confirmed on the final account are treated as waived. Timeliness of completion is therefore not a formal requirement: a measurement not taken before the work was concealed cannot be reconstructed, and estimating it afterwards is precisely what opens the way to dispute.

A specific mechanism operates where costs diverge from those assumed at tender. Price revision clauses are mandatory in the initial tender documents, and for works revision is triggered by a variation exceeding 3 per cent of the overall amount, operating to the extent of 90 per cent of the value exceeding that threshold and applying to performance still to be carried out. The mechanism works upwards and downwards, and should not be confused with a variation, which concerns a change in the subject of the performance. The distinction has immediate practical weight, because a cost increase caused by price movement is not managed as a variation.

The overall picture of the construction stage, with the roles and the sequence leading to payment, is in Construction works accounting in Italian practice. It also covers the regime governing reservations.

The body of rules around the bill is almost entirely public, but its usefulness in private work is unchanged and the differences of regime are worth spelling out. The differences of regime must nonetheless be made explicit.

In private work there is no obligation to prepare a bill, to adopt a particular price book, to produce a specification or to keep accounts in the forms of Annex II.14. That freedom does not amount to an absence of method. Without a bill, contractors' offers are not comparable and variations have no objective reference. Without a stated source, the estimate cannot be verified. Without a specification, technical requirements are left to the bill items, with the result that a dispute over the quality of a material finds no acceptance criterion. Without agreed accounting, the argument about progress reverts to the original quotation, which is never the right instrument for certifying what has been built.

Three practices cover most of the risk. Stating the source of rates together with its edition. Qualifying explicitly in the contract whether consideration is lump sum or measured, with the valuation basis and the frequency of measurement. Presenting the client with a budget structure separating the cost of the works from the other elements of the operation, with an explicit line for contingencies.

The recurring errors gathered along the whole route come down to a short and stable list. None of them requires special expertise to avoid.

A figure typed in place of an explicit calculation makes the bill impossible to update or verify, and at the first design change forces the take off to be redone. At the first design change it forces the document to be redone.

An item applied without reading its notes produces silent divergences that surface only during valuation, once the document is already contractual. By then the document has already become contractual.

A bill prepared before the design is stable diverges progressively from the design it is meant to describe. It is the most expensive error on the list.

A discrepancy between specification and bill transfers an unpriced obligation to the contractor, or prices work for which no acceptance criterion exists. Alternatively it prices work with no acceptance criterion.

Safety charges merged into the work items strip the component of the protection from discount that the law affords it. The effect shows directly in the tender amount.

A cost framework built by applying percentages to the bill total produces a document that is formally complete and without foundation. The percentages rest on no actual item.

A contingency provision omitted or token leaves the project without internal cover either for eventualities or for price revision. The gap covers both eventualities and price revision.

An interim valuation built on design quantities rather than measured ones attests the forecast and not the execution. The document thereby loses its function as a record.