The British Standard for topsoil, and the two things about it that are most often got wrong online — one of which will triple a topsoil order.
BS 3882:2015 is the current British Standard specifying topsoil for supply and use. It replaced BS 3882:2007. It covers classification, chemical and physical requirements, sampling, and — in Annex A — normative guidance on how topsoil should actually be used on site. Annex A is the part that matters for quantities, and the part almost nobody reads.
Spread topsoil should not normally exceed 300 mm. The rooting depths above are totals — topsoil on top, subsoil below. They are not topsoil depths.
This is the single most consequential misreading in the category. A calculator that offers "900 mm — trees" as a topsoil depth is quoting a rooting depth as though it were a soil order. A reader who follows it buys three times what the standard asks for, of the more expensive of the two materials. We have seen exactly that on a major UK calculator whose own standards page states the rule correctly.
It is not only wasteful. Deep topsoil stays wet, settles for years, and encourages roots to sit in it rather than going down.
Our topsoil calculator warns above 300 mm and tells you to run the depth below it as subsoil instead. That costs us nothing, because nobody pays us per tonne.
Premium, General Purpose and Economy were withdrawn with the 2007 edition. The 2015 standard classifies topsoil as Multipurpose or Specific Purpose, the latter subdivided into acidic, calcareous and low fertility.
The old grades are still quoted constantly — by suppliers, by calculators, and by sites that also carry an accurate standards page and contradict themselves. If a supplier offers you "BS 3882 Premium topsoil", they are quoting a specification that has not existed for a decade. That does not necessarily mean the soil is bad; it means the label tells you nothing.
Ask for the classification and the test certificate instead. Multipurpose topsoil to BS 3882:2015 has stated pH, organic matter, texture and contaminant limits, and a supplier selling it properly can produce the analysis.
Related: BS 8601:2013 specifies subsoil, and is what Annex A points to for the layer beneath. We cite it on the topsoil calculator but do not have a page for it, because there is little in it that changes a quantity.
This page is a summary, not the standard. BS 3882:2015 is published by BSI and is not free — if a specification depends on it, buy the standard rather than trusting any website, including this one. What we can tell you is which parts of it our figures rest on, and which of our figures come from somewhere else entirely.
All standards · Topsoil calculator · Our figures