# What Is a Consistency Class?
**A consistency class is a standardized classification that describes the workability of fresh concrete, indicating how easily it flows and can be placed. The most common method uses the slump test, with classes ranging from S1 (stiff) to S5 (very fluid).**
## Slump test classes (EN 206)
The European standard EN 206 defines the following slump classes:
| Class | Slump (mm) | Description |
|——-|———–|————-|
| S1 | 10 – 40 | Stiff |
| S2 | 50 – 90 | Plastic |
| S3 | 100 – 150 | Soft |
| S4 | 160 – 210 | Very soft |
| S5 | 220+ | Fluid |
## How the slump test works
A cone-shaped mold (the Abrams cone) is filled with fresh concrete in three layers, each compacted with 25 rod strokes. The mold is then lifted vertically, and the difference in height between the mold and the settled concrete is measured. This difference is the slump value.
## Choosing the right consistency class
The appropriate class depends on the application:
– **S1-S2** — Suitable for road construction and mass concrete where minimal flow is needed and vibration equipment is available.
– **S3** — The most commonly specified class for general building construction, offering good workability while maintaining shape.
– **S4** — Used for heavily reinforced elements where concrete must flow around dense rebar arrangements.
– **S5** — Applied in self-compacting concrete or situations where mechanical vibration is impractical.
## Factors affecting consistency
– Water-cement ratio
– Aggregate size and shape
– Use of plasticizers or superplasticizers
– Cement type and content
– Temperature and time since mixing
## Related terms
– Slump test
– Workability
– Water-cement ratio
– Self-compacting concrete
– Plasticizer
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