Concrete Compressive Strength Converter

Enter any concrete compressive strength value and instantly convert between PSI, MPa, kN/m², and kgf/cm². Covers every unit system used in US, European, and international construction.

Free to use No sign-up required Verified against ACI 318 & EN 206 All 4 major unit systems

✓ PSI ↔ MPa ↔ kN/m² ↔ kgf/cm² ✓ ACI & EN grade identification ✓ Works on any device ✓ Last verified May 2026

Reviewed by the AllConcreteCalculator.com editorial team — conversion factors cross-checked against ACI 318 and EN 206 standards, May 2026.

Enter a Compressive Strength Value

Compressive Strength Value

Enter any value — the converter outputs all four units simultaneously. Please enter a valid strength value greater than 0.

Common US Grades (PSI)

Common European Grades (MPa — EN 206)

All four unit systems appear instantly. No sign-up required.

Converted Strength Values

Converted Values — All Unit Systems

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PSI (lb/in²)

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MPa (N/mm²)

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kN/m²

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kgf/cm²

— Input

— Closest ACI Grade

— Closest EN 206 Grade

Concrete Classification

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Base unit: MPa (SI)
1 MPa = 145.038 PSI
1 MPa = 1,000 kN/m²
1 MPa = 10.1972 kgf/cm²

PSI → MPa: value ÷ 145.038
kN/m² → MPa: value ÷ 1000
kgf/cm² → MPa: value ÷ 10.1972

All other conversions go via MPa as intermediate step.

How to Use This Concrete Strength Converter

Identify your source unit. Before entering a value, select the correct input unit from the dropdown — PSI if you're working from US drawings, MPa if you have European or international specs, kN/m² for some civil engineering documents, or kgf/cm² for older metric specs and Japanese standards. Getting the unit right matters far more than the precision of the number itself.
Type or select your strength value. Enter the compressive strength from your mix design, structural drawings, or specification. Use the preset buttons for the most common US grades (2,500–6,000 PSI) or EN 206 grades (C16–C40) to load them instantly without typing. The converter accepts any positive value, including non-standard strengths used in high-performance concrete.
Read all four converted values simultaneously. The converter outputs PSI, MPa, kN/m², and kgf/cm² in one shot — no need to convert twice. The closest ACI (US) and EN 206 (European) standard grades are identified automatically, which is useful when adapting specifications across code systems.
Use the grade classification for spec compliance. The classification panel tells you what application the converted strength corresponds to — residential slabs, commercial structures, high-performance work, etc. Use this to verify that a converted specification still meets the structural intent of the original design before substituting concrete grades.

⚠ Pro Tip: PSI and MPa are not interchangeable labels — 4,000 PSI is approximately 27.6 MPa, not 4,000 MPa. The most common field error is reading a US PSI value on a metric spec sheet and assuming the unit is MPa. That's a 145× error in specified strength. Always verify the unit on every drawing sheet header before ordering concrete.

Concrete Strength Conversion Formulas

All conversions use exact SI-derived factors. MPa (megapascal) is the SI base unit for pressure and stress. Every other unit converts through MPa using fixed multipliers established in ASTM E380 and ISO 80000-4.

Step-by-step worked example — converting 4,000 PSI to all other units.
Step	Formula	Result
1. Input	4,000 PSI	4,000 PSI
2. PSI → MPa	4000 ÷ 145.038	27.58 MPa
3. MPa → kN/m²	27.58 × 1000	27,579 kN/m²
4. MPa → kgf/cm²	27.58 × 10.1972	281.2 kgf/cm²

Standard Concrete Grade Conversion Reference

Common concrete compressive strength values in all four unit systems. Derived from ACI 318 and EN 206 grade designations.
ACI Grade	EN 206 Grade	PSI	MPa	kN/m²	kgf/cm²
—	C12/15	2,176	15.0	15,000	153.0
2,500 PSI	≈ C16/20	2,500	17.2	17,237	175.8
3,000 PSI	≈ C20/25	3,000	20.7	20,684	210.9
3,500 PSI	≈ C25/30	3,500	24.1	24,132	246.1
4,000 PSI	≈ C28/35	4,000	27.6	27,579	281.2
4,500 PSI	≈ C30/37	4,500	31.0	31,026	316.4
5,000 PSI	≈ C35/45	5,000	34.5	34,474	351.5
6,000 PSI	≈ C40/50	6,000	41.4	41,369	421.8
8,000 PSI	≈ C55/67	8,000	55.2	55,158	562.4
10,000 PSI	≈ C70/85	10,000	69.0	68,948	703.1

EN 206 grades shown as characteristic cylinder strength (fck). ACI grades shown as f'c (28-day cylinder). Approximate equivalents only — codes differ in test method and confidence level.

What Compressive Strength Does My Project Need?

Compressive strength is the single most specified concrete property. Selecting the wrong grade — either too low (structural failure risk) or unnecessarily high (cost waste) — is one of the most consequential decisions in any concrete project.

Recommended minimum compressive strength by application type — US and international equivalents.
Application	Min PSI (f'c)	Min MPa (fck)	EN 206 Grade	Notes
Mass concrete, fill	2,000	13.8	C12/15	Not for structural use
Sidewalks, patios	2,500	17.2	C16/20	Minimum for foot traffic exposure
Residential slabs, footings	3,000	20.7	C20/25	ACI 318 minimum for most structures
Residential driveways	3,500	24.1	C25/30	Freeze-thaw: min 4,000 PSI / C28
Commercial slabs, columns	4,000	27.6	C28/35	Most common US commercial spec
Prestressed concrete	5,000	34.5	C35/45	ACI 318 min for prestressed members
High-rise columns, parking structures	6,000–8,000	41–55	C40–C55	Engineer review required
High-performance / special structures	10,000+	70+	C70+	Requires mix design engineer

Specifying higher strength than needed wastes money but rarely causes problems. Specifying too low creates a dangerous situation that may not manifest until years after construction. When in doubt on a residential project, move up one grade — the cost difference between 3,000 and 4,000 PSI ready-mix is typically $5–$15 per cubic yard, a minor fraction of total project cost.

Common Mistakes When Using Concrete Strength Units

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Confusing PSI with MPa without converting. This is the most dangerous mistake in international concrete work. Ordering "4,000 MPa" concrete when you meant "4,000 PSI" (27.6 MPa) is a 145× error. Any time you receive a spec sheet in a different unit system, convert every strength value explicitly — never assume the number is the same in both units.
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Mixing up characteristic strength (fck) and mean strength (fcm). EN 206 grades like C25/30 have two numbers: the cylinder characteristic strength (25 MPa) and the cube characteristic strength (30 MPa). ACI f'c is measured on cylinders. If you're comparing an EN cube strength to an ACI cylinder strength without converting, your comparison is wrong — cube strengths are typically 20–25% higher than cylinder strengths for the same mix.
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Treating 28-day strength as final strength. ACI f'c is a 28-day value, but concrete continues gaining strength for months and years. A 3,000 PSI mix might reach 3,600 PSI at 90 days. For load testing or form removal timing, using only the 28-day value is conservative — but never assume a mix has already "reached" its final strength before 28 days unless test results confirm early-strength mixes or accelerated curing.
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Not accounting for test specimen size and curing conditions. Compressive strength results vary significantly based on cylinder size (4×8 in vs 6×12 in), cube size (100mm vs 150mm), curing temperature, and testing age. Results from field-cured cylinders are often 10–20% lower than standard lab-cured specimens. Never compare test results directly without ensuring identical test conditions.
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Using bagged concrete bag labels as engineering specifications. Bag labels like "Quikrete 5000" or "Sakrete High Strength" refer to approximate f'c in PSI under controlled mixing conditions. Field-mixed concrete consistently underperforms bag spec if water-cement ratio is increased, proportions are eyeballed, or curing is neglected. Never substitute bag-label strength for a certified mix design on any structural element without independent testing.

Frequently Asked Questions

Divide the PSI value by 145.038 to get MPa. For example, 4,000 PSI ÷ 145.038 = 27.58 MPa. You can also use the approximation of dividing by 145 for quick field estimates — the error is under 0.03%. The converter above performs this calculation instantly and simultaneously outputs kN/m² and kgf/cm² as well.
3,000 PSI concrete is equivalent to 20.68 MPa. This is roughly equivalent to the EN 206 grade C20/25. It's the most common minimum specified strength for residential footings, foundations, and slabs in the US per ACI 318, and corresponds to 20,684 kN/m² or 210.9 kgf/cm².
f'c (pronounced "f prime c") is the specified 28-day compressive strength of concrete in the ACI code system. It's the minimum strength a concrete mix must achieve when tested on standard 6×12 inch cylinders at 28 days of age under standard laboratory curing conditions. Structural engineers use f'c as the basis for all concrete design calculations in US practice. The apostrophe (prime) distinguishes it from in-place or field strength, which may differ from the specified f'c.
PSI (pounds per square inch) is the US customary unit for concrete compressive strength. MPa (megapascal) is the SI metric unit, used in Europe, Australia, Canada, and international codes. They measure the same property — how much load per unit area concrete can withstand before failing. The conversion factor is 1 MPa = 145.038 PSI. Typical US residential concrete of 3,000 PSI equals about 20.7 MPa. Neither unit is more accurate than the other — they're just different scales.
ACI (American Concrete Institute) grades are expressed as f'c in PSI — the 28-day cylinder compressive strength with a 5% probability of falling below that value. EN 206 (European) grades are expressed as C(cylinder/cube) — for example, C25/30 means characteristic cylinder strength of 25 MPa and cube strength of 30 MPa. The two systems cannot be directly equated because they use different statistical confidence levels and test geometries. However, approximate equivalents exist: ACI 4,000 PSI ≈ EN C28/35, ACI 5,000 PSI ≈ EN C35/45. Always consult both code documents when adapting designs across code systems.
ACI 318-19 specifies a minimum f'c of 2,500 PSI (17.2 MPa) for general structural concrete, and a minimum of 3,000 PSI (20.7 MPa) for most standard residential and light commercial applications. For prestressed concrete members, the minimum is 5,000 PSI (34.5 MPa). Concrete exposed to freezing and thawing or deicing chemicals must be at least 4,500 PSI (31.0 MPa) with air entrainment. These are code minimums — project specifications often exceed them.
kN/m² (kilonewtons per square meter) is a pressure unit equal to 1 kilopascal (kPa). It's numerically equivalent to 1,000 Pa or 0.001 MPa. While MPa is the preferred unit for concrete strength in structural engineering, kN/m² appears in some civil engineering documents, load calculations, and soil mechanics contexts. The conversion is simple: 1 MPa = 1,000 kN/m². A standard 4,000 PSI mix equals 27,579 kN/m².
28 days is the standardized test age established by ACI and ASTM because ordinary Portland cement concrete reaches approximately 99% of its 28-day strength by that point, and strength gain slows significantly after that window. Testing at 28 days also provides a practical construction timeline — it gives enough time for form removal, early loading, and quality control decisions without waiting months for final strength. Seven-day tests are also commonly performed to predict 28-day results (typically 65–75% of 28-day strength at 7 days for standard mixes).
ACI defines high-strength concrete (HSC) as any mix with a specified f'c above 6,000 PSI (41.4 MPa). Ultra-high-performance concrete (UHPC) typically exceeds 14,500 PSI (100 MPa). High-strength concrete requires careful mix design — lower water-cement ratios, supplementary cementitious materials like silica fume or fly ash, and often superplasticizers for workability. It's used in high-rise building columns, long-span bridges, and precast elements where reducing member size or weight is critical. Handling, curing, and testing requirements differ from normal-strength concrete and must be specified explicitly.
kgf/cm² (kilogram-force per square centimeter) is a legacy metric unit for pressure and stress. It was widely used in Japan, much of Asia, and older European engineering documents before the SI system standardized MPa. It remains in use in some Japanese Industrial Standards (JIS) and older technical literature. The conversion is 1 MPa = 10.1972 kgf/cm², so a typical 28 MPa (4,000 PSI) concrete equals about 285 kgf/cm². When working with older Japanese or Asian structural drawings, verify whether the unit is MPa or kgf/cm² — the numbers look similar but differ by a factor of 10.