Most concrete slab calculators miss two things: rebar estimates and accurate depth presets. Honestly, that's a pain when you're planning a pour. When I poured a patio slab last year, I used three different calculators and got three different numbers. One said I needed 4.2 yards. Another said 5.1. The third didn't even ask about rebar. This calculator fixes that. It uses standard slab thickness presets (3, 4, 5, and 6 inches) based on NRMCA data. It also estimates rebar spacing and quantity based on your slab dimensions. No email required — just enter your numbers and go. Here's what you get: - **Cubic yards** of concrete needed - **Number of 80 lb bags** (if you're mixing yourself) - **Ready-mix cost range** (based on $110–$150 per yard) - **Labor cost estimate** (placement at $50–$100 per yard) - **Rebar estimate** (based on 18-inch grid spacing) - **Total project cost range** All pricing comes from industry averages — NRMCA, BLS, and HomeAdvisor. We update this every 90 days. Your local prices may vary, but this gives you a solid starting point.

Ready-Mix vs. Bag Concrete: Technical Selection Guide

1. Material and Cost Parameters

• Ready-Mix Concrete
  • Unit cost: $110–$150 per cubic yard (delivered)
  • Placement labor: $50–$100 per cubic yard
  • Recommended application: Slabs exceeding 1 cubic yard (~80 sq ft at 4 in. thickness)
• Bag Concrete (80 lb bags)
  • Unit cost: $5.00–$7.50 per bag
  • Yield per bag: 0.6 cubic feet
  • Labor: User-performed (no contractor cost)
  • Recommended application: Slabs under 1 cubic yard

2. Operational Comparison

• Ready-Mix
  • Advantages: Consistent mix design, zero on-site mixing labor, rapid placement
  • Disadvantages: Minimum delivery fees apply; batch adjustments are difficult after dispatch
• Bag Concrete
  • Advantages: Exact quantity control, no delivery minimums, high maneuverability in confined spaces
  • Disadvantages: Physically demanding mixing, batch consistency may vary, slower overall production

3. Selection Threshold (Tipping Point)

• Primary criterion: Material volume exceeding 1 cubic yard favors ready-mix for cost and time efficiency.
• Secondary criterion (4 in. thick slab):
  • Slab area > 100 sq ft → order ready-mix
  • Slab area ≤ 100 sq ft → use bag concrete

4. Special Case: Irregular Geometry or Tight Access

• If slab design includes non-rectangular shapes, curves, or narrow access

Once you get your numbers, here's the plan: 1. **Order ready-mix** — Call your local supplier with the cubic yard figure. Tell them the slab thickness and strength (3000 psi is standard for residential slabs). 2. **Buy bags** — If you're going the bag route, round up by 5-10%. You'd rather have extra than run short mid-pour. 3. **Plan rebar** — The calculator estimates rebar for a standard 18-inch grid. For driveways or heavy loads, you might want 12-inch spacing. Adjust accordingly. 4. **Budget for labor** — If you're hiring, expect $50–$100 per yard for placement. That's finishing, not forming or site prep. 5. **Add 10% waste** — Always. Concrete isn't forgiving. Spills happen. Forms bulge. Trust me. Based on real data, a typical 10x10 slab at 4 inches thick needs about 1.23 cubic yards. That's roughly 55 bags of 80 lb mix or one ready-mix truck. Cost runs $135–$185 for materials plus $60–$125 for labor if you hire out.

The calculator defaults to 4 inches — that's the standard for patios, sidewalks, and most residential slabs. But here's when you need thicker: - **3 inches**: Light-duty walkways, garden paths. Honestly, this won't work if your soil isn't compacted well. - **4 inches**: Patios, garage floors, shed slabs. The sweet spot for most DIY projects. - **5 inches**: Driveways with light vehicle traffic. Adds a safety margin. - **6 inches**: Driveways with heavy trucks, shop floors, commercial slabs. Strength matters too. 3000 psi concrete is typical for residential. 4000–5000 psi is better for driveways or areas with freeze-thaw cycles. The calculator doesn't estimate strength — that's a mix design choice you make with your supplier.

Short answer: yes, for most slabs. Rebar prevents cracking and holds the slab together if the ground shifts. The calculator gives you a rebar estimate based on an 18-inch grid pattern. That's standard for 4-inch slabs. For thicker slabs (6 inches), you might want 12-inch spacing. For thin slabs (3 inches), rebar might not fit — use wire mesh instead. One thing I learned the hard way: rebar needs to be in the middle of the slab, not on the ground. Use rebar chairs or bricks to lift it off the subgrade. Otherwise, it's useless.