10 October 2026 · 1 min read
C25/30 or C30/37? Choosing the right concrete class
What do the two numbers in a concrete class mean, and how do you know which class suits your project?
In a concrete class, the first number is the 28-day characteristic compressive strength (MPa) of a cylinder specimen and the second that of a cube. C30/37 therefore means 30 MPa on cylinders and 37 MPa on cubes.
What does the code say?
The Turkish Building Earthquake Code requires at least C25/30 for reinforced concrete structures. This is a minimum; basement walls, car parks and aggressive environments may need higher classes.
Who decides?
The concrete class is set in the structural design and approved by the design engineer. Send us the class and placement method; our technical team prepares a mix suited to the exposure class.
