Concrete Calculator — Cubic Yards, Bags & Cost
Convert length × width × thickness into cubic yards, equivalent 60-lb bag count, and dollar cost — with a 10% waste factor baked in because a half-truck return charge costs more than ordering extra.
Concrete Calculator
Enter project dimensions below — results update instantly. Switch units freely.
Estimates assume typical industry density and waste factors. Always verify with your supplier and local building code before purchasing material.
Why Concrete Short-Ordering Wrecks Your Project
Ready-mix trucks pour concrete in a continuous stream. Once the pour starts, the clock is running — concrete begins initial set at 30 minutes and reaches final set at 2-4 hours. If you run out mid-pour and have to wait for another truck, you get a cold joint that becomes a permanent structural weakness.
Three mistakes that wreck concrete estimates:
- Calculating on plan dimensions — not accounting for over-excavation or form flex
- Ignoring waste — 5-10% goes to spillage, form bleeding, and the inevitable last-bucket overrun
- Rounding down instead of up — suppliers charge for the truck capacity used; rounding up to the next quarter-yard costs $30-50, while a return trip costs $200-400
This calculator builds in a 10% waste default and outputs bag equivalents so you can pick between ready-mix trucks and bagged mix based on total volume.
The Concrete Volume Formula
27 is the number of cubic feet in a cubic yard (3 × 3 × 3).
Why 27? A cubic yard is a 3-ft cube. Each side is 36 inches. Three feet × three feet × three feet = 27 cubic feet. Every concrete calculation eventually hits this ÷ 27 step.
Bag equivalents:
- 60-lb bag yields 0.45 ft³ (about 2.2 bags per ft³)
- 80-lb bag yields 0.60 ft³ (about 1.67 bags per ft³)
- 40 bags of 80-lb ≈ 1 cubic yard
Ready-mix cutoff is typically 1 cubic yard — below that, bagged is cheaper; above that, ready-mix is cheaper and faster.
| Project | Cubic Feet | Cubic Yards | 60-lb Bags | 80-lb Bags | Best Method |
|---|---|---|---|---|---|
| Fence post hole (12×36 in) | 2.4 | 0.09 | 6 | 4 | Bags |
| Sonotube 10 in × 4 ft | 2.2 | 0.08 | 5 | 4 | Bags |
| Sidewalk 4 × 8 ft × 4 in | 10.7 | 0.40 | 24 | 18 | Bags |
| Patio 10 × 10 ft × 4 in | 33.3 | 1.23 | 74 | 56 | Ready-mix |
| Patio 14 × 14 ft × 4 in | 65.3 | 2.42 | 145 | 109 | Ready-mix |
| Garage slab 20 × 20 ft × 5 in | 166.7 | 6.17 | — | — | Ready-mix |
| Basement slab 30 × 40 ft × 4 in | 400.0 | 14.81 | — | — | Ready-mix |
Break-even between bags and ready-mix is typically ~1 cubic yard at 2026 pricing.
| Quantity | Ready-Mix $/yd³ | Surcharge | Total Effective $/yd³ |
|---|---|---|---|
| 1-3 yd³ (short load) | $165 | $85-150 min. fee | $195-215 |
| 4-6 yd³ | $160 | None | $160 |
| 7-10 yd³ | $155 | None | $155 |
| 11+ yd³ (full truck) | $150 | None | $150 |
| Weekend / overtime | +$30 | +$75-125 dispatch | varies |
Pricing excludes delivery distance surcharge ($3-8 per mile beyond 20 mi), unloading time overage ($1-3 per min after 5-7 min per yd³).
Real-World Example Calculations
Standard Patio 12 × 12 ft @ 4 in
Backyard entertainment patio, residential.
- Length
- 12 ft
- Width
- 12 ft
- Thickness
- 4 in
- Waste
- 10%
Takeaway: Break-even point — ready-mix is $327 vs. bags at $525. Take the ready-mix.
Two-Car Garage Slab 24 × 24 ft @ 5 in
Detached garage floor over compacted gravel base.
- Length
- 24 ft
- Width
- 24 ft
- Thickness
- 5 in
- Waste
- 10%
Takeaway: One truck delivery (10-yd³ capacity). Add 4,000 psi mix, vapor barrier, and wire mesh reinforcement.
Basement Slab 30 × 40 ft @ 4 in
New construction basement floor with radiant heat tubing.
- Length
- 40 ft
- Width
- 30 ft
- Thickness
- 4 in
- Waste
- 10%
Takeaway: Two truck deliveries at 8 yd³ each. Schedule 90 minutes apart. Confirm pump availability if pour is more than 50 ft from truck access.
Frequently Asked Questions
How many cubic yards of concrete do I need?
Calculate L × W × D (all in feet, convert inches by dividing by 12), then divide by 27. A 10×10 ft slab at 4 in thick = 10 × 10 × (4÷12) ÷ 27 = 1.23 cubic yards. Always add 10% waste: order 1.4 yd³.
How much concrete is in an 80-lb bag?
An 80-lb bag of concrete mix yields 0.6 cubic feet (≈ 0.022 cubic yards) of cured concrete. A 60-lb bag yields 0.45 ft³; a 40-lb bag yields 0.30 ft³. It takes about 45 bags of 80-lb to make 1 cubic yard.
Should I use bagged concrete or ready-mix?
Break-even is ~1 cubic yard. Below that, bagged is cheaper and doesn't require a truck. Above that, ready-mix is cheaper, faster, and produces a better continuous pour with no cold joints.
How much does a yard of concrete cost in 2026?
Ready-mix runs $150-180 per cubic yard for standard 4,000 psi mix. Short-load orders (under 4 yd³) add $85-150 in minimum fees. Specialty mixes (high-early, polymer-modified, fiber-reinforced) add $20-60 per yd³.
What is a short-load fee?
Concrete trucks hold 9-11 cubic yards. Orders under 4 yards typically incur a $85-150 minimum charge to cover the truck's lost capacity. Some suppliers call this a ‘short-load fee’ or ‘partial-load surcharge.’ Ask before ordering.
Can I pour concrete in winter?
Yes with precautions. Below 40°F, use hot water in the mix, accelerator additives, insulated blankets over the fresh pour, and/or propane heaters. Below 20°F, most contractors won't pour. Hydration needs to continue without freezing for 24-48 hours for proper strength gain.
How much waste should I add to my concrete order?
Standard recommendation: 10% for most residential pours. Add 15% for footings (over-excavation), 8% for flat slab work, 5% for perfectly formed pours like sonotubes. The cost of 10% extra material is always less than a return-trip for a short pour.