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Cross-market term

Slump and consistence

How workable fresh concrete is — how far a moulded cone of it subsides when the mould is lifted. American practice states a measured distance, European practice states a CLASS covering a range, and the two are not the same kind of number.
  • 4Markets
  • NoSame thing everywhere
  • 3Calculators

What it is called, by market

One concept, four markets. Where a name means something else locally, the card says so rather than leaving you to find out on site.

  • United Statesyours

    Same word, different thing

    slump

    also 4 inch slump, slump test

    A measured distance in INCHES, quoted as a target with a tolerance — a point value rather than a band.

  • Canada

    Same word, different thing

    slump

    also slump in mm

    The same test stated in millimetres, so a Canadian slump figure and an American one describe the same measurement in different units.

  • United Kingdom

    Same word, different thing

    consistence class

    also S1 to S5, slump class, slump in mm

    An S-class is a BAND of slump values, not a measurement — so S3 covers a range and cannot be converted to a single figure.

  • Australia

    Close, not identical

    slump

    also slump in mm

    Measured in millimetres as a value rather than a class, so Australian practice is closer to the North American convention than to the European one.

The governing standard, by market

  • United States

    ASTM C143

    Slump of hydraulic-cement concrete — the test method.

  • United Kingdom

    BS EN 12350-2 / BS EN 206

    Slump test method, and the consistence classes concrete is specified by.

Calculators for this

Each works in either measurement system, and the terminology on the page follows whichever market you have selected.

Concrete Mix Ratio Calculator →Concrete Calculator →ACI 211.1 Water-Cement Ratio Calculator →

Frequently asked questions

Can I convert an S-class to a slump figure?
Not to a single figure, because they are different kinds of quantity. A slump specified in inches or millimetres is a target value with a tolerance around it, so the concrete is accepted if it measures within that tolerance. A European consistence class such as S2 or S3 is a BAND: any slump inside the class's range conforms, and two loads at opposite ends of the same class behave noticeably differently on site. So an S-class maps to a range rather than a number, and a specification that converts a class to a single figure has narrowed it — which may be what was wanted, but it is a change to the specification rather than a translation of it.
Does a higher slump mean weaker concrete?
Not by itself, and this is the more damaging confusion. Slump measures workability, not strength. A mix can be made wetter by adding water, which does reduce strength because it raises the water-cement ratio — and that is where the association comes from. But it can also be made more workable by a plasticiser or superplasticiser at the same water content, which raises the slump and leaves the strength alone or improves it. So a high-slump mix arriving on site is not evidence of a weak one. What IS evidence of a weak one is water added at the site after batching, which is why specifications prohibit it and why the delivery ticket matters.
Why is the slump measured at all?
Because it is the only property of fresh concrete that can be checked in two minutes at the point of delivery, and because consistency between loads matters as much as the value. A load that arrives noticeably different from the last one indicates something changed at the plant or in transit, and that is worth knowing before it is placed. The test is also a conformity check: the concrete was specified at a consistence, and this is how the site establishes that what arrived matches. It says nothing about strength, which is established by cubes or cylinders tested later — so a load can pass the slump test and fail at twenty-eight days, and the two tests are not substitutes.