Thickness by use
| Use | Thickness | Who says so |
|---|---|---|
| Concrete floors on ground, including garages | 3½ in minimum | IRC R506.1 |
| Patios and walks | 3½–4 in “generally enough” | Ohio Ready Mixed Concrete Association |
| Driveway, passenger cars | 4 in minimum | Michigan Concrete Association |
| Driveway with delivery vehicles | 5 in minimum | Michigan Concrete Association |
The associations differ on driveways: Ohio’s guidelines treat 3½–4 in as generally enough for driveways, patios and walks, while Michigan’s set 4 in as the minimum for cars and 5 in where heavier vehicles will drive. If trucks will ever use the driveway — a moving van, a delivery, an RV — the thicker figure is the safer one.
What goes underneath
The IRC calls for a 4 in base course under slabs that sit below grade. A firm, evenly compacted base matters as much as thickness: a slab over a soft spot is likely to crack, and a base that dips makes the slab thicker — and the concrete order bigger — than you planned.
How strong the concrete should be
The IRC sets minimum compressive strength by how harsh the weather is where you live (Table R402.2). For the slabs most people pour:
| Element | Negligible weathering | Moderate | Severe |
|---|---|---|---|
| Interior slabs on ground (not garages) | 2,500 psi | 2,500 psi | 2,500 psi |
| Porches, steps and garage floors | 2,500 psi | 3,000 psi* | 3,500 psi* |
*With 5–7% entrained air, which helps concrete survive freeze–thaw cycles.
Michigan’s driveway guidelines go further: 4,000 psi with 6.5% ± 1.5% air. Quikrete rates its standard Concrete Mix at 4,000 psi at 28 days. Strength isn’t the only requirement, though: where the code calls for entrained air, confirm the mix you’re buying is air-entrained — ask the supplier or read the bag.
Local code wins
States and cities amend the IRC and decide which weathering category applies. Your building department and supplier know the local requirement.
Sources for the numbers on this page
- State of Ohio (adopted IRC text) — Residential Code of Ohio 4101:8-5-01 — R506.1 concrete floors on ground (3½ in minimum) · checked October 1, 2026
- State of Ohio (adopted IRC text) — Residential Code of Ohio 4101:8-4-01 — Table R402.2 minimum compressive strength; R403.1.4 footing depth · checked October 1, 2026
- Ohio Ready Mixed Concrete Association — Guidelines for durable driveways, patios and walks · checked October 1, 2026
- Michigan Concrete Association — Driveway and sidewalk guidelines · checked October 1, 2026
- Quikrete — Concrete Mix No. 1101 — technical data sheet (bag yields, strength gain, curing) · checked October 1, 2026
Corrections and updates are logged on the sources page.