What this calculator does
A concrete cylinder calculator, in the civil engineering sense, works out the compressive strength of a standard concrete test cylinder from the load that broke it. Concrete strength is checked by casting a cylinder of a set size, curing it, then loading it in a compression machine until it fails, and the strength that comes out of that test is what a batch of concrete is actually rated at against a specification.
The arithmetic behind the result is simple, strength equals failure load divided by the cross-sectional area the load acted over, but getting the area right depends on using the cylinder's actual diameter, not an assumed standard size. Enter the diameter of the cylinder tested and the load reading at failure, and this tool returns the compressive strength in both megapascals and psi.
The formula
Work out the cross-sectional area of the cylinder from its diameter, area = π × (diameter/2)². Divide the failure load by that area to get compressive strength in newtons per square millimetre, which is the same as megapascals. The psi figure is the same strength multiplied by the standard 145.038 conversion factor.
| Term | Meaning |
|---|---|
| Compressive strength | The maximum stress a concrete cylinder can carry before it fails in a compression test, in MPa or psi. |
| Failure load | The load reading on the compression testing machine at the moment the cylinder crushes, in newtons. |
| Cross-sectional area | The circular face of the cylinder that the load is applied over, calculated from its diameter. |
| Standard cylinder sizes | Concrete compressive-strength testing commonly uses 150 mm diameter by 300 mm tall cylinders, or a smaller 100 mm by 200 mm size, depending on the testing standard followed. |
The inputs explained
| Field | What to enter |
|---|---|
| Cylinder diameter (mm) | The diameter of the test cylinder, measured across the circular face the load is applied to, not its height. |
| Failure load (N) | The load shown on the compression testing machine at the point the cylinder fails, in newtons. |
When to use it
Checking a batch against a specified strength
A concrete pour is often specified to reach a strength such as 32 MPa at 28 days. Testing a cylinder from that batch and running the failure load through this calculation confirms whether the pour actually met the specification.
Comparing a lab report to a site record
A testing laboratory report usually states compressive strength directly, but recalculating it from the raw failure load and cylinder diameter recorded on site is a quick check that no transcription error crept into the reported figure.
Converting between MPa and psi for an overseas spec
A project specification written to a US standard may quote strength in psi while local test results come back in MPa, or the other way around, and having both figures from the one failure load avoids a manual unit conversion.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
Compressive strength for a standard 150 mm cylinder at increasing failure loads
A standard 150 mm cylinder tested to a range of failure loads.
| Failure load | Compressive strength | Compressive strength (psi) |
|---|---|---|
| 300 kN | 16.98 MPa | 2,462 psi |
| 400 kN | 22.64 MPa | 3,283 psi |
| 500 kN | 28.29 MPa | 4,104 psi |
| 565 kN | 31.97 MPa | 4,637 psi |
| 700 kN | 39.61 MPa | 5,745 psi |
| 850 kN | 48.10 MPa | 6,976 psi |
Compressive strength at a fixed failure load, by cylinder diameter
The same 500 kN failure load applied to cylinders of different diameters.
| Cylinder diameter | Compressive strength |
|---|---|
| 100 mm | 63.66 MPa |
| 125 mm | 40.74 MPa |
| 150 mm | 28.29 MPa |
| 175 mm | 20.79 MPa |
| 200 mm | 15.92 MPa |
Questions
What is the formula for concrete cylinder compressive strength?
Compressive strength equals the failure load divided by the cross-sectional area of the cylinder, where area = π × (diameter/2)². Load in newtons divided by area in square millimetres gives strength directly in megapascals.
What size cylinder should I use?
The two most common sizes are 150 mm diameter by 300 mm tall, and a smaller 100 mm by 200 mm cylinder. Either works with this calculator as long as the diameter entered matches the cylinder actually tested, since the result depends on that figure.
Is this the same as a basic cylinder volume calculation?
No. A plain cylinder volume calculation just multiplies the circular cross-section by height to get how much concrete fills a cylindrical shape, such as a post or column. This calculator instead uses the failure load from a compression test to find the material's strength, a different question entirely.
How do I convert the result to psi?
Multiply the MPa figure by 145.038, which this calculator does automatically alongside the MPa result, so both units are available from the one failure load reading.
For general force-over-area stress calculations outside the concrete testing context, see the mechanical stress calculator. To convert a strength figure between ksi and MPa for a US-standard specification, use the ksi to MPa converter.