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Calculate the compressive strength of concrete cubes and cylinders from the failure load and specimen dimensions. Useful for concrete testing, laboratory calculations and routine QA/QC work.
The compressive strength of concrete is determined by applying a compressive load to a concrete test specimen until failure. The compressive strength is calculated by dividing the maximum failure load by the loaded cross-sectional area of the specimen.
This calculator can be used for common concrete cube and cylinder test calculations by entering the specimen dimensions and the maximum failure load recorded during testing.
The basic compressive strength equation is:
When the failure load is entered in kN and the loaded area is expressed in mm²:
Since 1 MPa = 1 N/mm², the resulting value is directly obtained in MPa.
Consider a 150 mm × 150 mm × 150 mm concrete cube that fails under a maximum load of 900 kN.
150 × 150 = 22,500 mm²
900 kN = 900,000 N
900,000 ÷ 22,500 = 40 MPa
For a cylindrical specimen, the loaded area is calculated from its diameter.
For example, for a 150 mm diameter cylinder tested at a failure load of 700 kN:
| Cube Size | Loaded Area | Formula |
|---|---|---|
| 100 × 100 mm | 10,000 mm² | 100 × 100 |
| 150 × 150 mm | 22,500 mm² | 150 × 150 |
| 200 × 200 mm | 40,000 mm² | 200 × 200 |
Concrete specimens are commonly tested at specified ages such as 7 days and 28 days, depending on the project requirements and applicable standards.
The strength calculated from a single cube or cylinder is the compressive strength of that particular specimen under the specified test conditions.
It should not be confused with the characteristic compressive strength of a concrete grade, such as M25, M30, M35 or M40.
Concrete acceptance involves sampling, specimen testing, statistical evaluation where applicable, and the acceptance requirements specified by the relevant standard and project specification.
Verify sample ID, casting date, concrete grade and specified test age.
Check specimen dimensions and ensure the loaded faces are suitable for testing.
Confirm machine condition, calibration status and correct loading procedure.
Concrete compressive strength testing and concrete quality control should be carried out with reference to the applicable Indian Standards and project specifications.
| Parameter | Example |
|---|---|
| Concrete Grade | M40 |
| Specimen | 150 mm Cube |
| Test Age | 28 Days |
| Failure Load | 900 kN |
| Loaded Area | 22,500 mm² |
| Compressive Strength | 40.00 MPa |
| Remarks | Record as per laboratory/project format |
Compressive strength is calculated as failure load divided by the loaded cross-sectional area: f = P/A.
A 150 mm cube has a loaded area of 22,500 mm². Therefore, a 900 kN failure load gives a compressive strength of 40 MPa.
Concrete compressive strength is commonly expressed in MPa (N/mm²).
Yes. The cylinder calculation uses the circular loaded area, A = πD²/4.
No. The test age is important. A 7-day test result should not automatically be considered equivalent to the specified 28-day characteristic strength.
No. It calculates the compressive strength of the tested specimen. Concrete acceptance requires evaluation against the applicable standard, sampling requirements and project-specific acceptance criteria.
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