The denominator deserves attention
Two particulars can quote the same floor area without describing precisely the same thing. One figure may include spaces another excludes; one may be measured, another taken from an older plan. If the basis is unclear, a price-per-square-metre comparison may be less informative than it appears.
I would start with the source of the area. Who measured it, when, for what purpose and using which convention? The answer helps establish whether the figures can be compared directly or need further work.
Record the basis, not just the total
RICS guidance for its members and regulated firms says the basis of measurement should be documented and suitable for the instruction. Its current editions page distinguishes the published sixth-edition Code of Measuring Practice and IPMS: All Buildings from the proposed seventh edition (RICS, n.d.-a). The status should be rechecked when an instruction is agreed.
IPMS provides an international framework intended to make measurements more consistent (RICS, n.d.-b). Naming a standard is only useful if the actual calculation follows it. A reader should be able to understand the treatment of the relevant spaces and any measurement limitations.
A small arithmetic example
Suppose a fictional sale price is €300,000. Dividing by 100 square metres produces €3,000 per square metre; dividing by 120 produces €2,500. The price has not changed. The denominator has. This example illustrates why a seemingly precise rate can mislead when areas are not on a common basis.
Changing from square feet to square metres only changes the unit. It does not reconcile different definitions of the space being measured. If a garage, attic or other space is included, its treatment should be clear rather than left to the reader to infer.
Comparable evidence still needs judgement
RICS comparable-evidence guidance identifies the need for a common measurement or comparison standard before analysing transactions (RICS, 2023). Even when that is achieved, location, condition, layout and other circumstances can still affect how useful the evidence is.
For a rural house with several outbuildings, for example, one combined area may obscure more than it explains. A clear schedule can distinguish the elements and their uses. The purpose is to make the property understandable, not to produce the largest possible number.
Questions worth asking
Request the measurement basis, the date and source, the included and excluded areas, and any access limitations. If the figure is important to a purchase or lease, agree whether it needs independent verification.
Floor area also does not establish title, planning compliance or the suitability of a space for a proposed use. Keep those enquiries with the relevant advisers. A good measurement is an important piece of the evidence, rather than a substitute for the rest of it.
References
Download this article’s reference list ↓
Royal Institution of Chartered Surveyors (RICS) (n.d.-a) Code of measuring practice: editions and measurement basis. Available at: Code of measuring practice: editions and measurement basis (Accessed: 1 November 2026).
Royal Institution of Chartered Surveyors (RICS) (n.d.-b) International Property Measurement Standards. Available at: International Property Measurement Standards (Accessed: 1 November 2026).
Royal Institution of Chartered Surveyors (RICS) (2023) Comparable evidence in real estate valuation. 1st edn, originally published 2019; reissued 2023. Available at: Comparable evidence in real estate valuation. 1st edn, originally published 2019; reissued 2023 (Accessed: 1 November 2026).
Further reading
Blackledge, M. (2017) Introducing Property Valuation. 2nd edn. Routledge. Edition, context & purchase links View / buy at publisher
Shapiro, E., Mackmin, D. and Sams, G. (2019) Modern Methods of Valuation. 12th edn. Estates Gazette. Edition, context & purchase links View / buy at publisher
Chudley, R., Greeno, R. and Kovac, K. (2024) Chudley and Greeno’s Building Construction Handbook. 13th edn. Routledge. Edition, context & purchase links View / buy at publisher
Books listed for further reading have not necessarily been consulted in full. See the reading room for the basis of each recommendation.
General information for Irish property matters. The requirements of a particular instruction should be discussed with the appropriate professional. Editorial approach and source policy.
Put the guidance into practice
Explore the relevant service and what to prepareThe wider picture
Follow a guided reading route around this question.