Two documents, one source
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.
The adjective estimativo therefore carries the entire difference, and carries it on a specific plane. 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.
The comparison
| Aspect | Computo metrico | Computo metrico estimativo |
|---|---|---|
| Content | Description, unit of measurement, quantity | The same items plus unit rate and amount |
| Question answered | How much of it is being done | What it costs |
| Source required | Drawings and technical specification | Additionally a prezzario or a price analysis |
| Sensitivity to time | Low. Quantities do not age | High. Rates are tied to the date of design approval |
| Typical use | Checking quantities, comparing bids on unit rates | Establishing the works amount and the cost framework |
| Presence in public deliverables | Absorbed into the priced bill | Deliverable of the progetto esecutivo |
The row on sensitivity to time is the most useful in practice. An unpriced bill prepared two years earlier remains valid if the design has not changed. A priced bill prepared two years earlier needs revaluing, because rates must relate to the date of design approval and the prezzario applied has annual validity.
When only the unpriced bill is needed
There are situations in which the unpriced document has a function of its own. In those cases pricing would come too early.
Checking quantities is the first. When reviewing someone else's work, or when isolating a measurement error from a pricing error, separating the two planes is the quickest method: if the quantities reconcile, the problem lies in the choice of prezzario items.
Comparing bids on unit rates is the second. Giving contractors the schedule of operations and quantities and asking them to apply their own rates produces perfectly comparable bids, because the quantity base is identical for everyone.
Programming is the third. The construction programme, labour requirements and site logistics are built on quantities, not on amounts.
How you move from one to the other
The move requires three decisions, in order. Each conditions the one that follows.
Choosing the source of rates comes first: the regional prezzario in public works, a price book or reference list in private work. The choice is not neutral and should be stated in the document, together with the edition used.
Matching each bill item to a prezzario item comes next, and must be done by reading the list item's description in full rather than its heading alone. This is the step where the hardest errors to detect take root.
Determining the missing items closes the process. Where no prezzario item corresponds to the operation intended, the rate is built by analysis, documenting materials, labour, plant hire and transport and adding the prescribed percentages for overheads and profit.
How the document is presented
Beyond content, the two documents differ in the form in which they are issued, and form affects usability. The format decides whether the document can be worked on at all.
The unpriced bill appears as a schedule with description, unit of measurement, dimension lines and total quantity. The legibility of those dimension lines is its essential characteristic: an unpriced bill showing only totals cannot be verified and loses most of its usefulness.
The priced bill adds the unit rate and amount columns, and is normally accompanied by two derived deliverables: the summary by work category, which makes the incidence of each category on the total legible, and the schedule of unit rates applied. In public works the labour incidence schedule joins these.
One element that should always be stated and is often missing is the reference for the source of rates, giving the prezzario and its edition. Without it the amounts cannot be verified and the document cannot be updated.
The practical consequences of the distinction
The distinction produces concrete effects in three recurring situations. In all three the error stems from conflating the two documents.
When inviting bids from several contractors, issuing the unpriced bill allows comparable offers on the same quantity base. Issuing the fully priced bill instead anchors bids to the figures shown, reducing the information the comparison yields.
When managing a variation, separating the two planes establishes whether the cost increase stems from a rise in quantities or from a change in rates. That distinction changes the discussion with the client radically and, in public works, the regime applicable to the change.
When updating an estimate after some time, the unpriced bill remains usable and simply needs revaluing against the current prezzario. Rebuilding an obsolete priced bill from scratch while the quantities remain valid is avoidable work, and its avoidability depends on having kept the two planes separate in the working file.
Where the bill sits among estimating tools
The priced bill is not the only way to estimate the cost of a project, and it helps to know where it sits. Knowing the alternatives helps to choose one proportionate to the stage.
A parametric estimate per square metre works from average values by building type. It is quick, suited to the feasibility stage and to order of magnitude checks, but it does not allow items to be isolated and does not hold up as a contractual basis.
The computo metrico estimativo works from the operations the design actually requires. It presupposes a developed design and is the only instrument that allows cost to be discussed item by item.
A contractor's quotation expresses the price an operator asks to carry out those operations. It incorporates that firm's organisation, its purchasing and its margin, and can therefore diverge from the bill in either direction without either being wrong.
The most common misunderstanding in dealings with clients arises precisely here: the priced bill is read as the price that will be paid, whereas it is an estimate of the cost of the works according to a declared source. In private work the contract price arises from agreement between the parties.
The final account bill
A third variant completes the picture. The bill prepared on completion sets out the quantities actually executed, valued at contract rates. It is not a design document but an account, and in public works its function is performed by the accounting documents, which have the status of public instruments.
Comparing the design bill with the quantities actually valued, read item by item, is the most valuable information a project returns to whoever prepared the estimate. It shows where the method held and where it gave way, and allows subsequent estimates to be calibrated on the practice's own data.
Note: the legislative references in this page relate to Italy and are current as at the date of publication. Public procurement rules change frequently, and the version in force should be checked before any operational use.