When quantities are uncertain you can tender approximate quantities and remeasure, or tender rates alone and measure as you go. The two behave very differently on site.
Both routes accept that you do not know the quantities, and both pay the contractor for what is actually built. The difference is whether the tender contains an estimate of quantity at all. A bill of approximate quantities gives bidders a notional total to price against, which makes bids comparable but creates expectations about scale. A schedule of rates gives no total, which is honest about the uncertainty and much harder to evaluate.
Bill of approximate quantities at a glance
The documents contain a measured bill based on the best estimate available, clearly labelled as approximate. Bidders price every item, producing a tender total that is used for comparison and for early cash flow planning. The work is then remeasured as it is built and the final sum is calculated at the tendered rates. Significant departures from the estimated quantities usually trigger a right to review the affected rates.
Schedule of rates at a glance
The documents contain descriptions of work items with units but no quantities, and bidders insert rates. There is no tender total, so evaluation depends on applying a notional basket of quantities to each bidder rates. Work is instructed and measured as it proceeds, and payment follows the measured quantity at the tendered rate. The arrangement suits a stream of small, unpredictable works more than a single building.
Comparability of bids
Bill of approximate quantities: Good. Every bidder prices the same quantities, so the totals can be compared directly once qualifications are normalised.
Schedule of rates: Poor without effort. You must build a weighted basket of representative quantities and apply it to each schedule, and the weighting choices decide the winner.
Exposure to rate loading
Bill of approximate quantities: Moderate. A bidder can load rates on items it expects to grow and reduce rates on items it expects to shrink, which is why the estimate must be as honest as you can make it.
Schedule of rates: High. With no quantities disclosed, a bidder guesses which items will be instructed most and prices accordingly. Your basket is the only defence.
Cost certainty at award
Bill of approximate quantities: A tender total exists and is usable as a budget, with a clear understanding that it will move as quantities firm up.
Schedule of rates: None at award. The budget has to be built separately from your own forecast of the quantities you will instruct.
Measurement effort during the works
Bill of approximate quantities: Substantial and structured. Joint measurement of each element as it completes, against a stated method of measurement, with records signed by both parties.
Schedule of rates: Substantial and continuous. Every instruction has to be measured and agreed, often in small parcels, which generates a high volume of paperwork.
Behaviour when quantities move a long way
Bill of approximate quantities: Most forms allow a rate to be reviewed where the quantity changes materially, because the original rate assumed a certain scale of working.
Schedule of rates: The rate stands regardless of volume unless the schedule says otherwise, so a small instruction can be uneconomic and a very large one can be a windfall.
Administrative fit for the client team
Bill of approximate quantities: Needs a quantity surveyor familiar with the stated method of measurement and willing to go on site monthly.
Schedule of rates: Needs a disciplined instruction log and someone who records each small job as it happens, or the final account becomes unprovable.
When bill of approximate quantities wins
- Projects where the design is substantially complete but quantities depend on survey or opening up.
- Tenders where you need a comparable headline figure for approval or funding.
- Work with repetitive elements, such as a refurbishment of many similar units.
- Situations where you want competitive tension across the whole scope rather than item by item.
When schedule of rates wins
- Ongoing maintenance, fit out or repair programmes where instructions arrive piecemeal.
- Projects where the extent of work genuinely cannot be estimated, such as remedial work behind finishes.
- Term arrangements covering a portfolio of buildings over a period.
- Work that must start before the full scope is known, with no appetite for a provisional sum.
How to decide
If you can produce an estimate of quantities that you believe within a reasonable band, use approximate quantities and remeasure, because comparability at tender is worth a great deal. If any estimate you produce would be a fabrication, use a schedule of rates and invest the saved effort in building a realistic basket for evaluation and a tight instruction procedure for the works. Mixing the two across a single project is usually a mistake unless the boundary between them is physically obvious.
Test your choice by pricing a plausible final account under both routes using one bidder rates and your own quantity forecast. If the two answers are close, take the route with the lower administration burden. If they diverge sharply, the divergence shows you which items carry the real exposure, and those items deserve a firmer definition before you tender anything. Measurement conventions and standard documents are updated periodically, so verify which edition you are referring to before issuing the tender.
Domira builds and supervises projects across Saudi Arabia, and the commercial discipline above is how its projects stay inside their budget and their programme. Send the drawings, the contract or the site and Domira will tell you where the risk actually sits.
Frequently Asked Questions
What is the difference between a remeasured contract and a schedule of rates?
A remeasured contract starts from an estimated bill of quantities that bidders price, producing a tender total that is later adjusted by measuring the work actually built. A schedule of rates contains no quantities at all, so there is no tender total and payment is built entirely from measurement of instructed work. The first gives comparability at tender; the second gives flexibility during delivery.
How do you compare bids when there are no quantities?
You create a basket of representative quantities that reflects the work you expect to instruct, then apply each bidder rates to that basket to produce a comparable total. Weight the basket towards the items most likely to dominate spend, and keep the weighting confidential until bids are in. Publish the method of measurement so that every rate is understood to cover the same work content.
Can a tendered rate be changed if the quantity turns out very different?
Many forms allow a rate to be reviewed where the measured quantity departs materially from the estimate, on the basis that the original rate assumed a particular scale and sequence of working. Whether that right exists on your project depends on the drafting, so check the clause before relying on it. A legal adviser should confirm how the mechanism operates under the governing law of your contract.
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