Concrete Strength Grades (psi)
In the US, concrete is specified by f′c — the specified 28-day compressive strength, in psi, of a standard test cylinder. The grade drives the strength-based water-cement ratio and typical uses below.
Choose a grade
Grades at a glance
| f′c | Approx. metric | Typical uses |
|---|---|---|
| 2500 psi | ~17.2 MPa | Sidewalks (some jurisdictions), non-structural fill, very light-duty work |
| 3000 psi | ~20.7 MPa | Footings, foundation walls, non-structural slabs, general residential work |
| 4000 psi | ~27.6 MPa | Driveways, structural slabs, most commercial / structural work, exterior flatwork |
| 5000 psi | ~34.5 MPa | Columns, beams, heavily loaded members, high-durability applications |
| 6000 psi | ~41.4 MPa | High-rise columns, precast/prestressed concrete, high-durability applications |
Higher strength grades need a lower water-cement ratio and usually more cement. See the method page for how w/c is selected.
Minimum f′c set by exposure (ACI 318)
In the US, the structural design usually sets a minimum specified strength, but ACI 318's durability requirements can set a higher one. ACI 318-19 assigns exposure classes for freezing and thawing (F), sulfate (S), water contact (W) and corrosion protection of reinforcement (C), each with a maximum w/cm and a minimum f′c. Selected examples:
| Exposure class | Situation | Max w/cm | Min f′c (psi) |
|---|---|---|---|
| F1 | Freezing and thawing, limited exposure to water | 0.55 | 3500 |
| F2 | Freezing and thawing, frequent exposure to water | 0.45 | 4500 |
| F3 | F2 plus exposure to deicing chemicals | 0.40 | 5000 |
| S1 | Moderate sulfate exposure | 0.50 | 4000 |
| C2 | Reinforced, exposed to moisture and external chlorides | 0.40 | 5000 |
F-class concrete also requires entrained air. Check the edition of ACI 318 adopted by your jurisdiction and the full tables before specifying.
Residential work: the IRC table
For one- and two-family dwellings, the International Residential Code sets minimum strengths by weathering probability: typically 2500 psi for protected foundations and interior slabs, rising to 3000 or 3500 psi (air-entrained) for exterior walls, porches, steps and garage floors in moderate and severe weathering regions. Local amendments and ACI 332 may apply; check your jurisdiction.
What the testing lab will check
Strength is verified on cylinders (4×8 in or 6×12 in) made to ASTM C31 and tested to ASTM C39, usually at 28 days. For f′c up to 5000 psi, ACI 318 acceptance requires that the average of any three consecutive tests is at least f′c and that no single test falls more than 500 psi below f′c. The producer therefore designs for a required average strength f′cr well above f′c — with no history, f′c + 1200 psi for grades from 3000 to 5000 psi.
Frequently asked questions
What does psi mean?
Pounds per square inch — the unit for f′c, the specified 28-day compressive strength measured on a standard cylinder.
Which grade for a driveway?
4000 psi is commonly used for driveways and exterior flatwork, but always confirm the required grade against local codes and project specifications.