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Methodology & sources
Last reviewed: November 3, 2026. All calculators share one engine, so a figure is the same on every page. The tables below are generated from that engine when the site is built.
Volume
Slab, footing, wall: length × width × thickness
Round slab, tube, hole: π × (diameter ÷ 2)² × height
Square hole: side² × depth
Steps: width × run × rise × n(n+1)/2, plus any landing deeper than one run
Curb & gutter: length × (curb depth × (curb height + flag thickness) + gutter width × flag thickness)
All sizes are converted to feet first. 1 cubic yard = 27 cubic feet; 1 cubic metre = 35.3147 cubic feet. The waste allowance (10% by default) is added to the total before bags are counted, and bag counts are rounded up.
Bag yields
| Bag | Yield | Bags per cubic yard |
|---|---|---|
| 80 lb | 0.6 ft³ | 45 |
| 60 lb | 0.45 ft³ | 60 |
| 50 lb | 0.375 ft³ | 72 |
| 40 lb | 0.3 ft³ | 90 |
Source: QUIKRETE Concrete Mix No. 1101 data sheet. Other mixes (high-yield, fast-setting) differ; check the bag.
Bags or ready-mix
Up to 1 cubic yard we suggest bags; above 2 cubic yards, ready-mix; in between, compare prices (and any short-load fee). These thresholds are practical guidance, not a standard.
Gravel base and rebar
- Gravel base: slab area × base depth, plus the waste allowance, at 1.4 tons per cubic yard (crushed stone 1.35–1.4, road base up to 1.5: SelectSG).
- Rebar grid: 3 in clearance from each edge; bars in each direction = grid ÷ spacing rounded up + 1; plus 10% for laps and offcuts; sold as 20 ft bars (6 m metric). Method: Inch Calculator.
Fence posts
- Bury one third of the post's overall length, which equals half its height above ground, or go to the frost depth if that is deeper.
- Hole depth = buried depth + 6 in of gravel. Hole diameter = 3 × post width.
- Concrete fills from the gravel to 3 in below grade, minus the post.
Source: QUIKRETE, Setting Posts. Check: QUIKRETE Fast-Setting data sheet sets a 4 in post in a 10 in × 2 ft hole with two 50 lb bags; our formula gives 1.93.
Material weights
| Material | Default (tons/yd³) | Range | Sources |
|---|---|---|---|
| Gravel / crushed stone (¼–2 in) | 1.4 | 1.35–1.7 | SG, AM, IC |
| Pea gravel | 1.4 | 1.35–1.7 | SG, IC |
| Road base / crusher run | 1.5 | 1.4–1.5 | SG |
| River rock | 1.4 | 1.39–1.7 | AM, IC |
| Crushed limestone | 1.32 | 1.32–1.7 | AM, IC |
| Decomposed granite | 1.35 | 1.3–1.4 | SG |
| Sand (dry) | 1.35 | 1.3–1.5 | AM, IC |
| Sand (wet) | 1.6 | 1.5–1.7 | IC |
| Topsoil (dry) | 1.1 | 1–1.3 | SG, AM, IC |
| Fill dirt (compacted) | 1.4 | 1.3–1.5 | IC |
| Crushed asphalt / millings | 1.8 | 1.62–1.96 | IC |
| Mulch | 0.3 | 0.2–0.4 | AM, IC |
SG = SelectSG; AM = Aggregate Markets; IC = Inch Calculator. US short tons; 1 ton per cubic yard = 1.19 tonnes per cubic metre.
Costs
| Item | US average |
|---|---|
| Installed slab, plain (per ft²) | $4.00–$8.00 |
| Wire mesh / rebar (per ft²) | $0.20–$0.35 / $2.00–$3.00 |
| Stain / stamped / stamped elaborate (per ft²) | $3.50–$7.50 / $10.00–$14.00 / $18.00–$20.00 |
| Sealer / vapor barrier (per ft²) | $1.00–$2.00 / $0.50 |
| Ready-mix (per yd³) | $125 (typical $110–$165) |
| Short-load fee (under 8 yd³) | $60.00–$110.00 flat |
| 80 lb bag | $6.29 |
Sources: This Old House (updated March 2026), Inch Calculator, Lawn Love (updated October 2026). Costs are national averages for budgeting; local quotes decide the real price. Visitors can type their own prices.
Limits
pourplot estimates quantities for planning. It does not design structures. For footings, foundations and anything load-bearing, follow your plans, an engineer and your local building code.
Change log
- November 3, 2026: site launched with the sources above.