Quantity calculation file: trace the BOQ back to its sources
A quantity calculation file connects the quantity in a bill of quantities to the work behind it. It records the source, calculation, location in the project and assumptions that affect the result. This makes it possible to investigate an item, review a drawing revision and identify missing information before pricing. The agreed deliverable and available project documents determine the level of detail; the number of worksheets alone says little about its usefulness.
What belongs in a quantity calculation file?
The bill of quantities brings together item descriptions, units and quantities for its agreed purpose. The calculation workbook explains how those quantities were established. Each item has an identifiable worksheet with its item code, description, unit, a link to the corresponding BOQ row and the calculation breakdown. A cover sheet and contents list make the workbook easier to navigate. Read it alongside the bill of quantities so that the scope described in the item is checked as well as its total.
The worksheet identifies the drawing, revision or data table used as a source. When a model is involved, it records the export and the available location or element identifiers. A cell reference alone is insufficient if the reader cannot tell what that cell represents. A short explanation beside the formula should state what was measured, the resulting unit, and the parts included or deducted. Keep notes and legends close to the table so they remain understandable in an exported copy.
Separate measurements, assumptions and missing information
A dimension read from a drawing, a quantity exported from a model and an adopted calculation factor are different kinds of information. Link the measurement or quantity to its source. Put the factor in a separate cell with its explanation, source and date. If a required input is unavailable, identify the gap and the question that must be resolved. A blank input is not zero, and using an assumption in a formula does not turn it into a measured fact.
A working formula does not establish that its source is correct. A workbook can calculate without errors while relying on an old drawing, counting an area twice or omitting work that was not shown. Identifiable sources, measurement boundaries and the reasons for professional decisions are therefore part of the record.
For example, the volume calculation for part of a slab may use an area and a thickness taken from different sources. Before multiplying them, check unit compatibility, the area being measured and whether the thickness varies. Thickened areas and openings are dealt with according to the documents and the agreed measurement method. This illustrates the explanation a worksheet needs; it is not a universal slab formula or a pricing instruction.
Break quantities down by floor, apartment and element
Where the source material supports it, divide the quantity by floor, zone and apartment while retaining a clear route back to the item total. This can help with reviewing flooring, plaster, paint, openings or sanitary fixtures. If an apartment selection is still missing, leave it explicitly open. Do not fill in a material choice or order quantity without a basis. The breakdown should let a reviewer examine each part without losing its connection to the overall BOQ.
An attached sketch should identify the location being measured. A frame around the element and a clear mark beside the relevant dimension or quantity help explain the calculation. Include the drawing reference and revision. An unmarked image of an entire floor does not explain which part belongs to the item. A readable caption also helps the reviewer return to the source instead of relying solely on colour or a reduced image.
Before using the breakdown for procurement, distinguish the physical quantity, the pricing quantity and the order quantity. Waste allowances, packaging, supply lengths and material selections may affect ordering and should remain separate from the measured amount. The guide to quantity types in a project explains these distinctions.
Review the workbook before delivery and after changes
Start by matching the item codes, descriptions and units between the calculation workbook and the BOQ. Then check formulas, summation ranges, source references and duplicate entries in the breakdown. The difference between the calculated total and the BOQ quantity should be zero when both represent the same item and revision. A zero difference establishes numerical agreement between those two locations. It does not establish that the measurement is complete or that the drawings were interpreted correctly.
Professional review against the drawings and specifications is also needed. Where a discrepancy appears, record its cause and how it was addressed. The quantity cross-checking guide explains how to investigate differences between sources. A quantity surveyor may be an engineer or a registered building technician, like Yaakov Avital. The quantity surveyor defines the measurement scope and examines what the figures mean, alongside the spreadsheet work.
When revised drawings arrive, retain the previous workbook version and record what changed, when and why. Update the affected calculations and check the totals again. This makes a calculation correction distinguishable from a design change. The delivery record should identify the revisions used, any assumptions still awaiting resolution and the update scope that was agreed.
Frequently asked questions
Can the quantity calculation file be delivered in Excel?
An Excel workbook with calculation sheets, formulas and references can be included in the agreed deliverable. The level of detail and required source material should be defined before work starts. Receiving a workbook does not replace checking its actual scope and the information that remains missing.
Does every item need a sketch?
A sketch is useful when it explains a location or measurement boundary. For an item based on a table or a list of components, a clear source reference may be more useful than another drawing. In either case, the calculation needs an identifiable basis that can be reviewed, rather than an unrelated image.
What information is needed to define the work?
Provide the available drawings and revisions, a model if one exists, specifications and schedules, the purpose of the BOQ and the project stage. Include any existing BOQ or earlier calculation with its date. Reviewing this material allows the deliverables, unresolved questions and scope of the written proposal to be defined.
Have a project? Tell me briefly what the project is and what already exists. When the project is a good fit, I usually reply with focused questions and a written quote.
Contact me for a quote* Created with AI for marketing, for illustration only. Not reviewed by Yaakov Avital and not professional advice. Every project must be checked on its own by a professional quantity surveyor and an engineer.