Benchmarking is a technique for comparing projects in a systematic way, usually looking at quantitative metrics such as costs, energy performance or space usage. The prime purpose of such comparisons is to find out what other clients are doing, getting a sense of what is normal, and then using that information to set targets for ones own project. For the purpose of briefing, spatial data are usually the most interesting. This may concern the allocation of space per user (e.g. floor area per student, per office worker, per patient) or the allocation of space for specific functions (e.g. the amount of conference space per workplace, or the amount of outdoor space per pupil). Such data can be used as input for early calculations of the size of a project, or as a baseline to test ones own standards for space usage, getting a feel for whether these are generous or tight. Benchmarking data, however, should be treated with care. Overly hasty comparisons may ignore the specifics and particularities of a project and lead to the wrong outcomes. It is thus important to look at the building behind the data. What kind of buildings have been included in the benchmark? A benchmark of inner-city office buildings, for example, will produce different results from one that compares suburban office buildings. And how many buildings have been included in the benchmark? Just a few or large numbers, which make the data more trustworthy? Last but not least, one should look closely at what kind of data is being benchmarked. What unit of measurement has been used? Do figures relate to gross floor area or usable floor area or rentable area and how have these been defined? Small differences in definitions can result in large differences in the data. Recommendations-Look carefully at how the benchmark dimensions have been defined. What is included in the figures and what not? -Check out where the data come from: are they based on actual measurements or on a questionnaire? The latter tends to provide less accurate, less reliable data.-Do not just copy and paste data from benchmarks. Benchmark data can only be a starting point for a more thorough client-specific analysis.-Have a discussion about where the client would like to be in a benchmark: best in class or within the normal range?-Consider doing the benchmarking yourself: seek out comparable projects, analyse their data, and combine the benchmarking with a project visit.