Ordering concrete is one of those tasks where precision pays off immediately. Order too little and the truck leaves before you finish — now you are scrambling for bags from the hardware store to fill the last corner. Order too much and you are paying for concrete with nowhere to put it. Both scenarios cost money and time. Here is how to get the number right.
Why divide by 27? Because 1 cubic yard = 3 ft × 3 ft × 3 ft = 27 cubic feet. Ready-mix concrete is sold by the cubic yard in the US (or cubic meter in metric countries).
| Shape | Formula | Common Use |
|---|---|---|
| Rectangle/Slab | L × W × D / 27 | Driveways, patios, garage floors |
| Circular slab | π × r² × D / 27 | Round patios, fire pit pads |
| Wall/Footing | L × H × W / 27 | Foundation walls, stem walls |
| Column/Pier | π × r² × H / 27 | Deck piers, Sonotube footings |
| Trench footing | L × W × D / 27 | Continuous footings, grade beams |
| Steps | Sum of individual step volumes | Porch steps, stairways |
A driveway 20 ft long, 12 ft wide, 5 inches thick:
Volume = 20 × 12 × (5/12) / 27 = 20 × 12 × 0.417 / 27 = 100 / 27 = 3.70 cubic yards
With 10% waste: 3.70 × 1.10 = 4.07 → order 4.25 yards
8 footings, each 12 inch diameter (r = 0.5 ft), 48 inches deep (4 ft):
Volume per footing = π × 0.5² × 4 / 27 = 3.14 × 0.25 × 4 / 27 = 0.116 cubic yards
Total = 8 × 0.116 = 0.93 cubic yards
With waste: approximately 1.0 cubic yard
A foundation wall 80 ft perimeter, 8 ft tall, 8 inches wide:
Volume = 80 × 8 × (8/12) / 27 = 80 × 8 × 0.667 / 27 = 426.7 / 27 = 15.8 cubic yards
With 5% waste: 16.6 → order 17 yards
3 steps, each 4 ft wide, 7.5 inch rise, 11 inch run, plus a 4 ft × 4 ft top landing 4 inches thick:
| Project Type | Waste Factor | Why |
|---|---|---|
| Flat slab on grade (formed) | 5–7% | Minor subgrade unevenness |
| Slab on grade (unformed edge) | 10–15% | Edges spread without forms |
| Foundation walls | 3–5% | Well-formed, minimal waste |
| Trench footings (earth-formed) | 10–20% | Irregular trench walls absorb concrete |
| Pumped concrete | Add 3–5% | Line priming and residual in the pump |
| Factor | Ready-Mix (truck delivery) | Bagged (60/80 lb bags) |
|---|---|---|
| Best for | Over 1 cubic yard | Under 0.5 cubic yards |
| Cost per yard | $130–$200 | $250–$400 (bag equivalent) |
| Mix consistency | Excellent (plant-batched) | Varies (hand or machine mixed) |
| Labor | Minimal — truck pours | Significant — mixing bag by bag |
| Timing | Must pour all at once | Work at your own pace |
At $5–$7 per 80 lb bag, one cubic yard from bags costs $210–$294 in materials alone — before your labor mixing them. Ready-mix is almost always cheaper above 0.5 yards.
| Cost Component | Typical Range |
|---|---|
| Ready-mix concrete (per yard) | $130–$200 |
| Delivery charge | $0–$50 (often included within 20 miles) |
| Short-load fee (<minimum) | $50–$100 |
| Saturday/overtime pour | $50–$150 surcharge |
| Pump truck (if needed) | $150–$300/hour (2-hour minimum typical) |
| Fiber reinforcement (per yard) | $5–$10 |
| High-strength upgrade (4000+ PSI) | $10–$20/yard over standard 3000 PSI |
Estimate your concrete volume with our Concrete Calculator and plan foundation dimensions with the Footing Calculator.
Residential patios and walkways: 4 inches. Garage floors and driveways for cars: 4-5 inches. Driveways for heavy vehicles (RVs, trucks): 5-6 inches. The extra inch from 4" to 5" adds only about 25% more concrete but roughly doubles the slab's load capacity.
About 42 bags of 80-lb concrete or 56 bags of 60-lb concrete per cubic yard. Each 80-lb bag yields approximately 0.6 cubic feet of mixed concrete (0.022 cubic yards).
3,000 PSI: walkways, patios, non-structural slabs. 3,500 PSI: driveways, garage floors. 4,000 PSI: foundations, structural columns, commercial floors. 4,500+ PSI: freeze-thaw exposure, bridge decks, special structural applications. Most residential work uses 3,000-3,500 PSI.
Concrete reaches about 70% strength in 7 days and 99% in 28 days (at 70°F). You can walk on it after 24-48 hours. Drive on a driveway after 7 days. Full cure for maximum strength and durability: 28 days. Keep it moist for the first 7 days (curing compound or wet burlap) for best results.
Ready-mix should be placed within 60-90 minutes of batching (or 300 drum revolutions). In hot weather, this window shrinks. Tell the dispatch your pour rate so they time truck arrivals to avoid delays. Retarders can extend workability in extreme heat.