Concrete Strength Calculator
Cylinder break strength in psi or MPa.
What it does
Cylinder breaks grade concrete. A press crushes standard cylinders at 28 days, and load over area gives psi or megapascals. A 6 inch cylinder breaking at 141,400 lb reads 5,001 psi on 28.27 square inches.
The tool above divides either unit pair. Defaults give 5,001 psi imperial with a 500 kN on 150 mm mirror at 28.3 MPa. A 4 inch cylinder at 50,000 lb gives 3,979 psi. Area carries the whole divisor, so diameter errors square.
Standards fix the procedure behind the division. Six by twelve inch cylinders (150 by 300 mm) with moist curing to 28 days make breaks comparable across labs. Air content, aggregate, and temperature then explain most scatter.
This page divides loads only. It does not cure cylinders, approve pours, or replace lab reports. Structural calls need tested breaks.
How to use
- Pick imperial (lb, in) or metric (kN, mm).
- Enter the breaking load.
- Enter the cylinder diameter.
- Read strength first.
- Read area to check the divisor.
- Compare against the specified grade.
Formula
- load
- Breaking machine load in lb or kN.
- d
- Cylinder diameter in inches or mm.
- area
- Pi d squared over four.
Breaking load over cross area on standard cylinders at 28 days. At zero load there is no strength. Curing, air, and aggregate sit outside this division.
Worked example
Example: 5,000 psi break
Defaults: imperial 141,400 lb on 6 in diameter. Metric mirror is 500 kN on 150 mm.
- Inputs (imperial default): 141,400 lb on a 6 in cylinder.
- Area: pi times 36 / 4 is 28.27 in2 area.
- Strength: 141400 / 28.27 is 5,001 psi.
- Metric mirror (500 kN on 150 mm) gives 28.3 MPa.
- Standard 6x12 in cylinders cured 28 days. Tool shows the same.
Reference table
| Break | Strength | Area |
|---|---|---|
| 141400 lb on 6 in | 5,001 psi | 28.27 in2 area |
| 500 kN on 150 mm | 28.3 MPa | 17671 mm2 area |
| 50000 lb on 4 in | 3,979 psi | 12.57 in2 area |
| 300 kN on 100 mm | 38.2 MPa | 7854 mm2 area |
| 80000 lb on 6 in | 2,829 psi | 28.27 in2 area |
Limits
- Division only. No lab procedure.
- 28 day standard assumed.
- No air or curing model.
- Single break. Statistics need sets.
Common mistakes
- Using cube area for cylinders.
- Mixing lb with mm areas.
- Reading early breaks as 28 day grade.
- Ignoring diameter tolerance.
- Approving pours from one break.
Try it yourself
Quick checks. Answers sit tucked under each question.
500 kN on 150 mm?
Area is pi times 22500 / 4 is 17671 mm2 area. Strength is 500000 / 17671 is 28.3 MPa.
50,000 lb on 4 in?
Area is 12.57 in2 area. Strength is 50000 / 12.57 is 3,979 psi.
Questions
How is strength figured?
Load / area. Here 5,001 psi on 28.27 in2 area.
How is cylinder area figured?
Pi d squared / 4. Here 28.27 in2 area.
Which cylinder size?
6 by 12 in (150 by 300 mm) cured 28 days is the standard pair.
How do psi and MPa relate?
Strength / 145 for rough MPa, or MPa times 145 for psi. Here 28.3 MPa.
Does this grade my pour?
No. Air, curing, and aggregate shift real breaks from the math line.
Can I skip lab testing?
No. Lab breaks only. Field approval needs cylinders and a lab.