Methodology & prices
Every number on this site is derived from the assumptions below. Prices are reviewed quarterly.
Volume
Concrete volume is width × length × thickness. Dimensions are in feet and thickness in inches (converted to feet by ÷ 12). Cubic feet are divided by 27 for cubic yards, and by 35.3147 for cubic meters. We apply a default 10% waste allowance to the ordered volume — adjustable per calculation.
Bag yields
Bags are the volume ÷ the bag yield, always rounded up (you can't buy part of a bag):
| Bag size | Yield (ft³) | Typical price |
|---|---|---|
| 80 lb | 0.600 | $7.00 |
| 60 lb | 0.450 | $6.00 |
| 50 lb | 0.375 | $6.25 |
| 40 lb | 0.300 | $5.50 |
Cost assumptions (January 2026)
All prices are national US averages held in a single source file and shown as an honest low–high range:
- Ready-mix delivered: $125–$190 per cubic yard, plus a short-load fee on pours under 10 yd³.
- Installed slab: $6–$12 per square foot for a 4" slab, +$0.75/sq ft per extra inch of thickness.
- Gravel base: $30–$65 per cubic yard delivered.
- Bedding sand: $28–$58 per cubic yard delivered.
- Rebar: $7.00–$13.00 per 20 ft #4 stick.
Costs vary widely by region, mix design, site access, prep and finish. Regional multipliers in the calculator (Northeast, West, Midwest, South) shift the range but are deliberately coarse — they are a guide, not a quote. Always get local quotes before you buy or pour.
Base gravel, rebar & sand
The "You'll also need" figures assume a 4" compacted gravel base (with a 15% compaction order allowance), a two-way #4 rebar grid at 18" on-center on 20 ft sticks, and a ~1" bedding sand layer.
Sources
- ACI — American Concrete Institute (standards) ↗
- QUIKRETE — Concrete Mix bag yields ↗
- SAKRETE — Concrete Mix coverage ↗
- HomeAdvisor / Angi — Concrete cost data ↗
These calculators are provided for planning and estimation only and are not professional engineering or cost advice. See our about page for more.