# Concrete Strength Converter

Convert between grade, MPa, psi and kgf/cm², with cube-to-cylinder correction.

- Page: https://jianzhujisuan.com/en/concrete-strength-convert
- Category: Concrete (https://jianzhujisuan.com/en/c/concrete)
- Chinese version: https://jianzhujisuan.com/zh/concrete-strength-convert.md
- Data checked: 2026-10-25

## Quick result

With the default inputs (Grade C30, Specimen 150 mm cube, Measured strength (optional) 0 MPa): **Cube strength 30.0 MPa**

## Inputs

| Parameter | Type | Default | Unit | Note |
|---|---|---|---|---|
| Grade | select | C30 | — |  |
| Specimen | select | 150 mm cube | — |  |
| Measured strength (optional) | number | 0 | MPa | Leave 0 to use the grade value; enter a result to back-calculate the grade |

## Formula

- **Cylinder strength**: f_cyl = 0.79 × f_cube (up to C50)
- **psi**: 1 MPa = 145.038 psi
- **kgf/cm²**: 1 MPa = 10.197 kgf/cm²
- **Elastic modulus**: Ec = 10⁵ ÷ (2.2 + 34.7/fcu) MPa

## Worked example

C30: 30.0 MPa cube strength — 23.7 MPa as a cylinder (3438 psi, or 4351 psi as a cube) and 306 kgf/cm² — with fc = 14.3 MPa, ft = 1.43 MPa and Ec = 2.98×10⁴ MPa.

## Questions

### Does C30 mean 30 MPa?

C30 means a characteristic cube strength of 30 MPa at 28 days under standard curing, with 95% confidence. That is not the design value: the design compressive strength of C30 is only 14.3 MPa after the material partial factor and the prism-to-cube correction. Designing with 30 MPa would be badly unsafe.

### Why convert between cube and cylinder?

A cube benefits less from platen restraint and reads higher; a cylinder is closer to the stress state in a real member, so the same concrete tests about 21% higher as a cube. China and Europe use cubes, the US and Japan use cylinders — convert when reading foreign drawings or you will misread the grade.

### Can a test result be converted back to a grade?

Only with the age and curing conditions stated. Direct comparison requires 28-day standard curing; site-cured or early-age specimens must first be normalised to 28 days by maturity or an accepted curve. A single failing result does not condemn the concrete — the code allows cores taken from the structure.

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