Concrete Strength Class Chart — EC2 C-Classes & Typical US Mixes
EN 1992-1-1 Table 3.1 classes C12/15–C50/60 with fck, cube strength, fcm, fctm and Ecm, plus typical US f′c mixes 2500–8000 psi with MPa conversions.
Updated August 18, 2026
A European concrete class like C25/30 names two numbers at once: the characteristic cylinder strength fck (25 MPa) and the characteristic cube strength fck,cube (30 MPa), both at 28 days with 95% of tests expected to pass. Everything else Eurocode 2 needs — the mean strength fcm, the mean tensile strength fctm, and the secant modulus Ecm — is tabulated in EN 1992-1-1 Table 3.1 and reproduces exactly from the code’s own formulas: fcm = fck + 8 MPa, fctm = 0.30·fck^(2/3), and Ecm = 22·(fcm/10)^0.3 GPa. The values below are the printed table figures; the formulas give the same numbers after rounding.
American practice specifies a single number instead: the specified compressive strength f′c from cylinder tests, quoted in psi. There is no official US "class" table, so the second chart lists the f′c levels that ready-mix suppliers actually stock and what each is typically ordered for, with exact MPa conversions. When comparing systems, compare cylinder to cylinder: a 4,000 psi mix (f′c ≈ 27.6 MPa) sits between C25/30 and C30/37 by cylinder strength — do not match it against the cube number in the class name.
EN 1992-1-1 Table 3.1 — Strength & Deformation (C12/15–C50/60)
| Class | fck, cylinder (MPa) | fck,cube (MPa) | fcm (MPa) | fctm (MPa) | Ecm (GPa) |
|---|---|---|---|---|---|
| C12/15 | 12 | 15 | 20 | 1.6 | 27 |
| C16/20 | 16 | 20 | 24 | 1.9 | 29 |
| C20/25 | 20 | 25 | 28 | 2.2 | 30 |
| C25/30 | 25 | 30 | 33 | 2.6 | 31 |
| C30/37 | 30 | 37 | 38 | 2.9 | 33 |
| C35/45 | 35 | 45 | 43 | 3.2 | 34 |
| C40/50 | 40 | 50 | 48 | 3.5 | 35 |
| C45/55 | 45 | 55 | 53 | 3.8 | 36 |
| C50/60 | 50 | 60 | 58 | 4.1 | 37 |
Printed Table 3.1 values. Derived columns follow the code formulas fcm = fck + 8, fctm = 0.30·fck^(2/3) (valid ≤ C50/60, rounded to 0.1 MPa) and Ecm = 22·(fcm/10)^0.3 (quartzite aggregates, rounded to whole GPa) — adjust Ecm ±10–30% for limestone, sandstone or basalt aggregates per EC2 §3.1.3.
Typical US Ready-Mix Strengths — f′c Usage Bands
| f′c (psi) | f′c (MPa) | Typical use |
|---|---|---|
| 2500 | 17.2 | ACI 318 minimum f′c for structural concrete; footings and walls in mild, non-freezing exposure |
| 3000 | 20.7 | Residential footings, foundation walls, and interior slabs-on-grade — the most common residential order |
| 3500 | 24.1 | Driveways, porches, and steps in severe weathering regions (IRC R402.2 minimum, air-entrained); garage slabs |
| 4000 | 27.6 | Structural slabs and beams, exterior flatwork in freeze–thaw climates, commercial slabs-on-grade |
| 5000 | 34.5 | Columns and walls in mid-rise construction, precast and prestressed products, high-traffic pavements |
| 6000 | 41.4 | High-strength columns and cores, prestressed girders — mix design and testing per project specification |
| 8000 | 55.2 | High-rise columns and cores and special precast; requires trial batches and tight QC (high-strength concrete) |
f′c is specified cylinder strength at 28 days; MPa column is the exact conversion at 0.00689476 MPa/psi, rounded to 0.1. Uses are typical NRMCA/PCA-consistent guidance — the governing drawings and exposure class requirements (ACI 318 Ch. 19) always control the minimum for a specific element.
Sources & Further Reading
- EN 1992-1-1:2004 (Eurocode 2) Table 3.1 — adjudicated across eurocodeapplied.com (computed values) and engipedia.com (printed table) reproductions; both consistent
- ACI 318-19 Table 19.2.1.1 (2,500 psi structural minimum) and IRC Table R402.2 (weathering-driven minimums for exterior flatwork)
- NRMCA / PCA published guidance on typical ready-mix strength selection; psi→MPa at 0.00689476 MPa/psi (NIST SP 811)
Frequently Asked Questions
What do the two numbers in a class like C25/30 mean?
The first is the characteristic 28-day cylinder strength fck (25 MPa on a 150×300 mm cylinder), the second the characteristic cube strength (30 MPa on a 150 mm cube). Cubes test roughly 20–25% higher than cylinders because the platens confine the shorter specimen more. Eurocode design formulas use the cylinder value fck.
How do I compare a US 4000 psi mix to a European class?
Convert and compare cylinder to cylinder: 4,000 psi × 0.00689476 = 27.6 MPa, which lands between C25/30 (fck 25) and C30/37 (fck 30). The common mistake is matching 27.6 against the second number in the class name — that one is a cube strength and would understate the European mix by a full class.
Is fcm = fck + 8 something I can design with?
fcm is the expected mean of the strength population, used for stiffness (Ecm depends on fcm) and creep/shrinkage models — not for section capacity. Capacity uses fck reduced by the partial factor (fcd = αcc·fck/γc). Producers target the mean so that no more than 5% of results fall below fck.
Why does my supplier quote a different E than Ecm in this table?
Table 3.1 Ecm assumes quartzite aggregates. EC2 §3.1.3 tells you to cut the value by 10–30% for limestone and sandstone and raise it up to 20% for basalt, and measured moduli vary further with the actual mix. For deflection-critical work, specify and test the modulus rather than reading it from the class.
Try the Calculators
Concrete Strength Class Chart — EC2 C-Classes & Typical US Mixes — reuven.tools/reference/concrete-strength-classes — verified against: EN 1992-1-1:2004 (Eurocode 2) Table 3.1 — adjudicated across eurocodeapplied.com (computed values) and engipedia.com (printed table) reproductions; both consistent; ACI 318-19 Table 19.2.1.1 (2,500 psi structural minimum) and IRC Table R402.2 (weathering-driven minimums for exterior flatwork); NRMCA / PCA published guidance on typical ready-mix strength selection; psi→MPa at 0.00689476 MPa/psi (NIST SP 811)