Concrete, rebar, and polymers, down to the number
What the psi on the ticket promises, how far apart the bars go, and which coating holds up in the sun. Each guide shows its sources, so you can check the figure before you pour.
Calculators
Run the takeoff before you call the supplier.
Guides by material
14 guides across three subjects, each with a short answer up top and the reasoning below it.
Concrete
Mix ratios, strength ratings, curing, and why slabs crack.
- Cement vs Concrete: What's the Difference?
- How Long Does Concrete Take to Cure?
- Concrete PSI Explained
- Concrete Mix Ratio: The 1-2-3 Rule
- Why Concrete Cracks
- What Is Efflorescence on Concrete?
- Types of Cement Explained
Reinforcement
Rebar sizes, grades, spacing, and composite bars that never rust.
- Rebar Sizes Explained
- Fiberglass Rebar vs Steel (GFRP)
- What Is Rebar?
- Rebar Spacing for a Concrete Slab
Quick reference
The two tables people look up most. Full versions live in the guides.
| Bar | Diameter | Area (sq in) | lb per ft |
|---|---|---|---|
| #3 | 3/8 in | 0.11 | 0.376 |
| #4 | 1/2 in | 0.20 | 0.668 |
| #5 | 5/8 in | 0.31 | 1.043 |
| #6 | 3/4 in | 0.44 | 1.502 |
| #7 | 7/8 in | 0.60 | 2.044 |
| #8 | 1 in | 0.79 | 2.670 |
The bar number is the diameter in eighths of an inch. See the full rebar size chart for #9 through #18.
| psi | Typical use |
|---|---|
| 2,000 to 2,500 | Non-structural fill, some footings |
| 3,000 | Residential slabs, footings, walls |
| 3,500 to 4,000 | Driveways, garage floors, patios |
| 4,000 to 5,000 | Structural columns, heavy floors |
| 5,000 and up | Bridges, high-rise, industrial |
Your local code and climate set the minimum. Read concrete psi explained before you order.
How we check our work
We write for builders, students, and homeowners who want the reason behind the rule.
Read our editorial policyWhere the figures come from
Figures come from ASTM and ACI standards, OSHA and DOE guidance, and university materials courses. We link what we can.
When a guide changed
Every guide shows when we published it and when we last changed it, so you know how fresh the numbers are.
How to report an error
Spot an error? Tell us with a source. We fix confirmed mistakes and update the date.