Concrete Calculator
Calculate cubic yards of concrete for slabs, footings, columns, and stairs. Includes bag counts and cost estimates.
Concrete needed
How concrete is measured and ordered
US ready-mix concrete is sold in cubic yards(27 ft³ each). A standard mixer truck holds ~10 yd³. Most suppliers have a minimum order of 1 yd³ and charge a “short load” fee on orders under 4–7 yd³ to recover delivery costs. For small jobs (under 1–1.5 yd³), bag mix from a home center is often cheaper after factoring in the short-load fee.
Slab thickness — what to actually use
- Sidewalk / walkway: 4" (3" in mild climates is acceptable but minimum).
- Patio: 4"
- Garage floor (cars): 4"
- Garage floor (trucks/RVs): 5–6"
- Residential driveway (cars): 4"
- Driveway (heavy vehicles, RVs): 5–6"
- Shed foundation: 4"
- Pole barn / workshop floor: 5–6" depending on equipment
- Footing: depth depends on local frost line and load — check code.
Always include reinforcement: 6×6 wire mesh (cheap, easy) or #3 / #4 rebar grid for heavier loads. The mesh/rebar prevents cracks from propagating across the slab when (not if) it cracks.
Mix strength (psi) — pick the right one
- 2,500 psi: rarely used — minimum for most residential applications.
- 3,000 psi: residential slabs, sidewalks, patios. The default at most ready-mix plants.
- 3,500–4,000 psi: garage floors, driveways subject to freeze-thaw, structural slabs.
- 4,500–5,000 psi: heavy-duty industrial floors, structural columns.
- 6,000+ psi: high-rise structural elements. Specialty mix.
Stronger mix costs $10–25 more per yard. For most residential work, 3,500–4,000 psi with air entrainment (in freeze-thaw climates) is the sweet spot.
Bag mix vs ready-mix: when to use which
Use bag mix when: project is under 1.5 yd³, access is limited (no truck access), you have a small mixer or just need to fill post holes / set fence posts. Mix in batches as needed. Standard 80-lb bag = 0.6 ft³.
Use ready-mix when: project is over 1.5 yd³, you need consistent quality, you want to finish the pour quickly. The truck pours where you need it (or into wheelbarrows / pumps). Time pressure: ready-mix typically must be discharged within ~90 minutes of leaving the plant.
Common mistakes
- Underestimating the waste factor — 10% is standard. Less for tightly-formed jobs, more for irregular shapes or rough subgrade.
- Forgetting the form takes up volume — the inside dimensions of the form are what you pour. Subtract any internal blockouts (drains, plumbing, etc.).
- Pouring on dry, hot ground — the soil sucks moisture from the mix, weakening it. Dampen subgrade before pouring.
- Adding too much water on-site — every gallon over the slump spec drops PSI by 200–500. The mix is engineered; don't weaken it.
- Skipping rebar / mesh — concrete cracks. Reinforcement keeps cracks tight and structurally insignificant.
- No control joints — saw-cut joints every 8–12 ft (slabs ≤4") within 24 hours of pouring forces cracks to happen at the joint, not in random places.
- Not curing properly — concrete needs 7+ days of moisture to reach design strength. Cover and mist, or use a curing compound.
Order planning checklist
- Calculate volume × 1.10 (waste).
- Round up to nearest 0.25 or 0.5 yard (most suppliers sell in quarter or half-yard increments).
- Confirm minimum order and short-load fees with your supplier.
- Schedule based on weather (avoid pouring above 90°F or below 40°F without admixtures).
- Have all forms, rebar, and tools ready BEFORE the truck arrives — concrete sets fast.
- Confirm truck access — measure the path width, overhead clearance, and turnaround space.
- Plan for waste disposal of any leftover material (some suppliers will take it back).
Pair this with our Unit Converter for any measurement conversions you need, and the Loan Calculator if financing a larger construction project.