Key numbers
- psi = pounds per square inch of compressive strength at 28 days (1 psi = 6.895 kPa; 3,000 psi ≈ 20.7 MPa)
- IRC Table R402.2: 2,500 psi minimum everywhere; garage floors and porches rise to 3,000 (moderate) and 3,500 psi (severe weathering), air-entrained
- ACI 318-19 Table 19.3.2.1: F0 2,500 psi, F1 3,500, F2 4,500, F3 5,000 psi for freeze-thaw exposure
- Bagged mix: QUIKRETE Concrete Mix and Sakrete High-Strength are rated 4,000 psi at 28 days, 2,500 psi at 7 days
On this page
- How to use the Concrete PSI Guide
- What does concrete psi mean?
- What psi does the IRC require? (Table R402.2)
- What psi does ACI 318 require by exposure class?
- 2500 vs 3000 vs 4000 psi: which do you need?
- How do you order concrete by psi? (worked example)
- How fast does concrete reach its psi?
- Common concrete psi mistakes
- Frequently asked questions
How to use the Concrete PSI Guide
- 1Pick your unitsEvery dimension has its own unit menu (in, ft, yd, cm or m); changing one converts that number so the size stays the same. The US / Metric switch sets all fields to feet and inches or meters and centimeters and resets them to typical values.
- 2Enter the dimensionsType the length (default feet), width (default feet) or thickness (default inches). Measure the inside of the forms and the depth in several places.
- 3Set waste and quantityUse the waste slider (0 to 20%, default 10%) and allow more on uneven ground. If you have several identical pours, enter how many.
- 4Read the resultsSee the volume in cubic yards, cubic feet and cubic meters, the ready-mix order rounded up to ¼ yard, the number of 90, 80, 60, 50 and 40 lb bags rounded up, and the weight at the density you choose (150, 145 or 140 lb/ft³).
- 5Price it and save itPick a pricing basis (per cubic yard, per cubic meter or per bag of the highlighted size) and enter your local price for a material cost. Use Add to project to total several pours, and Copy link to share the exact result.
Results update as you type. Back to the calculator ↑
What does concrete psi mean?
Concrete psi is the compressive strength, in pounds per square inch, that the mix is specified to reach 28 days after placing. “3,000 psi concrete” means test cylinders of that mix must reach at least 3,000 psi at 28 days. Building codes set the minimum by what the concrete is used for and how harsh the weather is.
The strength is measured by crushing cylinders under ASTM C39, the test QUIKRETE cites for its Concrete Mix rating. Footnote a of IRC Table R402.2 confirms the code numbers are “Strength at 28 days psi.” Metric specs use MPa:
| Specified strength (psi) | MPa (1 psi = 6.895 kPa) | Where you meet it in this guide |
|---|---|---|
| 2,500 | 17.2 | IRC minimum for all residential concrete; ACI F0, S0, W0, W1, C0, C1 |
| 3,000 | 20.7 | IRC garage floors, porches and exposed walls, moderate weathering |
| 3,500 | 24.1 | IRC garage floors and porches, severe weathering; ACI F1 |
| 4,000 | 27.6 | Bagged premix rating; ACI S1 and W2 |
| 4,500 | 31.0 | ACI F2 and S2 |
| 5,000 | 34.5 | ACI F3 and C2 |
QUIKRETE prints its 4,000 psi rating as 27.5 MPa on the data sheet; the 27.6 above is the straight 6.895 kPa conversion. Treat the code values as minimums: a designer can always specify more.
What psi does the IRC require? (Table R402.2)
The International Residential Code sets 2,500 psi as the floor for every type of residential concrete, and raises it only for concrete exposed to the weather in moderate and severe weathering regions. Your region comes from IRC Table R301.2(1), which your local building department fills in.
Below is Table R402.2, “Minimum Specified Compressive Strength of Concrete,” as adopted without change in the Residential Code of Ohio (OAC 4101:8-4-01, where it is numbered 402.2). Values are f’c in psi at 28 days.
| Type or location of concrete construction | Negligible weathering (psi) | Moderate weathering (psi) | Severe weathering (psi) |
|---|---|---|---|
| Basement walls, foundations and other concrete not exposed to the weather | 2,500 | 2,500 | 2,500 c |
| Basement slabs and interior slabs on grade, except garage floor slabs | 2,500 | 2,500 | 2,500 c |
| Basement walls, foundation walls, exterior walls and other vertical concrete work exposed to the weather | 2,500 | 3,000 d | 3,000 d |
| Porches, carport slabs and steps exposed to the weather, and garage floor slabs | 2,500 | 3,000 d, e, f | 3,500 d, e, f |
The footnotes, quoted from the same text:
- a. “Strength at 28 days psi.”
- b. “See Table 301.2(1) for weathering potential.”
- c. “Concrete in these locations that is subject to freezing and thawing during construction shall be air-entrained concrete in accordance with Footnote d.”
- d. “Concrete shall be air-entrained. Total air content (percent by volume of concrete) shall be not less than 5 percent or more than 7 percent.”
- e. “See Section 402.2 for maximum cementitious materials content.”
- f. “For garage floors with a steel-troweled finish, reduction of the total air content (percent by volume of concrete) to not less than 3 percent is permitted if the specified compressive strength of the concrete is increased to not less than 4,000 psi.”
Section R402.2 adds that fly ash, slag, silica fume and blended cements in garage floors and exterior porches, carport slabs and steps exposed to deicing chemicals are capped at the percentages in ACI 318 Section 19.3.3.4.
States amend this table. Minnesota Rules 1309.0402 replaces it with a version that adds a footings row at 5,000 psi in all three regions. Its footnotes allow 2,500 psi with an approved water- and vapor-resisting admixture, and exempt post footings for decks or porches, wood foundations, slab-on-grade foundation walls and footings for floating slabs. Always check the edition and amendments your jurisdiction has adopted.
What psi does ACI 318 require by exposure class?
ACI 318, the building code for structural concrete, sets a minimum strength and a maximum water-cementitious materials ratio (w/cm) for each exposure class. The table below is from ACI CODE-318-19(22) Table 19.3.2.1, as reproduced by Obla and Lobo in Concrete International (May 2023). When a member falls in several categories, the most restrictive value governs.
| Exposure class | Condition | Max w/cm | Min f’c (psi) | Min f’c (MPa) |
|---|---|---|---|---|
| F0 | Not exposed to freezing and thawing | N/A | 2,500 | 17.2 |
| F1 | Freezing and thawing, limited exposure to water | 0.55 | 3,500 | 24.1 |
| F2 | Freezing and thawing, frequent exposure to water | 0.45 | 4,500 | 31.0 |
| F3 | Freezing and thawing, frequent water and deicing chemicals | 0.40 | 5,000 | 34.5 |
| S0 / S1 / S2 | Sulfate exposure, none to severe | N/A / 0.50 / 0.45 | 2,500 / 4,000 / 4,500 | 17.2 / 27.6 / 31.0 |
| S3 | Very severe sulfate (option 1 / option 2) | 0.45 / 0.40 | 4,500 / 5,000 | 31.0 / 34.5 |
| W0 / W1 | Dry, or in contact with water without low-permeability need | N/A | 2,500 | 17.2 |
| W2 | In contact with water, low permeability required | 0.50 | 4,000 | 27.6 |
| C0 / C1 | Dry, or moist without external chlorides | N/A | 2,500 | 17.2 |
| C2 | Moist with chlorides from deicers, salt or seawater | 0.40 | 5,000 | 34.5 |
The ACI commentary examples cited in the same article: F2 covers members subject to snow and ice accumulation and “horizontal and vertical members in contact with soil”; F3 covers members exposed to deicing chemicals, such as horizontal members in parking structures. If in doubt between F1 and F2, the article says to pick F2.
Freeze-thaw classes also need entrained air. For 3/4 in (19 mm) stone, Table 19.3.3.1 targets 5.0% air for F1 and 6.0% for F2 and F3; the article notes the specified air may be reduced by 1 percentage point at f’c of 5,000 psi or more. Air content is set by your mix design and engineer, not by this summary.
IRC or ACI? Houses built under the IRC use Table R402.2. ACI 318 governs engineered structural concrete, and IRC Section R402.2 points to ACI 318 Chapters 19 and 20, or ACI 332, for concrete materials and testing. The two tables differ because the IRC is a prescriptive residential code; a licensed engineer decides which applies to a given element.
2500 vs 3000 vs 4000 psi: which do you need?
Use the code row for what you are building, then the weathering or exposure class for where you live. Higher psi is never below code, but it costs more and, at the ready-mix plant, usually means a richer mix.
| Project | IRC minimum (negligible / moderate / severe), psi | Notes |
|---|---|---|
| Interior slab on grade, basement floor | 2,500 / 2,500 / 2,500 | Air entrainment if it freezes during construction (footnote c) |
| Footings and foundations not exposed to weather | 2,500 / 2,500 / 2,500 | Some states amend this (Minnesota: 5,000 psi footings) |
| Exposed foundation walls, exterior walls | 2,500 / 3,000 / 3,000 | Air-entrained 5–7% where 3,000 applies |
| Garage floor, porch, carport slab, exterior steps | 2,500 / 3,000 / 3,500 | Air-entrained 5–7%; 3% allowed for a steel-troweled garage floor at 4,000 psi |
| Driveway, sidewalk, patio | Not listed by name | Ask your building department; the garage-floor row is the closest residential analogy |
Bagged premix gives you 4,000 psi on paper: QUIKRETE Concrete Mix No. 1101 and Sakrete High-Strength Concrete Mix are both rated 4,000 psi at 28 days on their data sheets. That clears every IRC row. The psi rating does not tell you the air content, so where footnote d applies, confirm with the manufacturer that the product meets the 5–7% air requirement before using bags. Ready-mix is ordered by psi and air content directly.
Strength is not the whole spec
Footnote d’s 5–7% air matters as much as the psi in freeze-thaw areas, and adding water on site to make concrete easier to place lowers the strength the mix was designed for. Ask for the psi, slump and air content on the delivery ticket.
How do you order concrete by psi? (worked example)
Work out the volume, add your extra, and tell the supplier the strength in psi at 28 days along with slump, stone size and air content. NRMCA’s guide to ordering ready-mix (CIP 31) lists those items, notes 3,500–5,000 psi is typical, and recommends ordering 4–10% extra.
Worked example: 12 × 20 ft garage floor, 4 in thick, moderate weathering
- Volume: 12 × 20 × (4 ÷ 12) = 80 ft³, or 2.96 yd³
- With 10% extra: 3.26 yd³ (2.49 m³); rounded to a quarter yard, order 3.5 yd³
- Strength: IRC Table R402.2, garage floor slab, moderate weathering: 3,000 psi (20.7 MPa) minimum, air-entrained 5–7%
- Same slab from 80 lb bags: 147 bags at 0.60 ft³ each, including the 10% extra, rated 4,000 psi but check air entrainment
The site’s calculator above returns the yards and bags; the psi comes from your code row, not from the volume.
Metric: a 4 × 6 m garage slab 100 mm thick is 2.4 m³, or 2.64 m³ (3.45 yd³) with 10% extra. In a severe weathering area the IRC row asks 3,500 psi, about 24.1 MPa, air-entrained.
How fast does concrete reach its psi?
The rating is a 28-day number. QUIKRETE rates its Concrete Mix at 2,500 psi (17.2 MPa) at 7 days and 4,000 psi (27.5 MPa) at 28 days, so after one week it has 62.5% of its rated strength. Its data sheet asks for 5 days of moist curing at 70 °F or more, 7 days at 50–70 °F, and 48 hours of protection from freezing.
Cold, dry curing slows strength gain. Our concrete curing time guide covers when you can walk, drive and build on a new slab; this page stays with the strength classes.
Common concrete psi mistakes
- Assuming one psi fits every job. The IRC asks 2,500 psi for an interior slab and up to 3,500 psi for an exposed garage floor in the same house.
- Ordering psi without air. In moderate and severe weathering areas the IRC requires 5–7% entrained air on exposed slabs and walls.
- Reading a mix ratio as a strength. A 1:2:3 site mix has no rated psi; a mix ratio is not a strength test. For a stated strength, use a tested mix design or a rated premix.
- Ignoring state amendments. Minnesota’s footing row at 5,000 psi is one example; check what your jurisdiction adopted.
- Treating psi as load capacity. Slab thickness, base and reinforcement decide what a slab carries; that is engineering, not a table lookup.
All values on this page are code minimums quoted for reference. Structural design must follow your local code and a licensed engineer.
FAQ
Frequently asked questions
What psi concrete do I need for a driveway?
The IRC strength table does not list driveways by name. Its closest row, garage floor slabs and porches exposed to weather, sets 2,500 psi with negligible weathering, 3,000 psi with moderate and 3,500 psi with severe, air-entrained. Your local code and engineer set the actual figure.
Is 3000 psi or 4000 psi concrete better?
4,000 psi is stronger and, in a ready-mix order, usually means a lower water-cement ratio, which helps durability. Whether you need it depends on the code row and exposure: IRC Table R402.2 tops out at 3,500 psi for residential work, while ACI 318 asks 4,500–5,000 psi for F2 and F3 exposure.
What psi is a bag of Quikrete concrete?
QUIKRETE Concrete Mix No. 1101 is rated 4,000 psi (27.5 MPa) at 28 days and 2,500 psi (17.2 MPa) at 7 days, tested under ASTM C39, per its data sheet. Sakrete High-Strength Concrete Mix states the same 4,000 psi at 28 days.
What is the minimum psi for a garage floor?
2,500 psi in a negligible weathering area, 3,000 psi in moderate and 3,500 psi in severe, per IRC Table R402.2. In moderate and severe areas it must be air-entrained at 5–7%, or 3% for a steel-troweled floor if strength is raised to 4,000 psi.
What psi concrete for footings?
IRC Table R402.2 lists 2,500 psi for foundations and other concrete not exposed to the weather, in all three weathering regions. Some states amend this; Minnesota's rule 1309.0402 sets footings at 5,000 psi. Check your adopted code and the footing design.
What does 3000 psi concrete mean?
It means test cylinders of that mix are specified to reach at least 3,000 pounds per square inch (about 20.7 MPa) of compressive strength at 28 days. It is a specified minimum, not the strength on day one.
How long until concrete reaches its rated psi?
The rating is for 28 days. Bagged QUIKRETE Concrete Mix is rated 2,500 psi at 7 days, 62.5% of its 4,000 psi 28-day figure. Curing temperature and moisture change this; see our concrete curing time guide.
How do I order ready-mix by psi?
Give the supplier the specified strength in psi at 28 days, plus slump, maximum stone size and air content, per NRMCA's ordering guide (CIP 31). NRMCA notes 3,500–5,000 psi (25–35 MPa) is typical, and that you should order 4–10% extra.
7 Sources
- IRC Table R402.2 as adopted in the Residential Code of Ohio, OAC 4101:8-4-01 (Cornell LII)
- Minnesota Rules 1309.0402, amendment to IRC Table R402.2
- Obla & Lobo, Selecting Exposure Classes and Requirements for Durability, Concrete International, May 2023 (ACI CODE-318-19(22) Table 19.3.2.1; NRMCA copy)
- ACI FAQ: chloride concentration in soil and exposure classes (C2: w/cm 0.40, 5,000 psi, ACI 318-19)
- QUIKRETE Concrete Mix No. 1101 data sheet (4,000 psi at 28 days, ASTM C39)
- Sakrete High-Strength Concrete Mix technical data sheet
- NRMCA CIP 31, Ordering Ready Mixed Concrete
Last reviewed October 10, 2026 by M Bilal. Found an error? Tell us.