How to use this calculator
- Enter Length in ft.
- Enter Width in ft.
- Enter Thickness in in — or tap a preset badge to auto-fill a typical value.
- Enter Price per cu yd in $.
- Press Calculate. The highlighted row is your order quantity; the note beneath it translates the number into real-world terms.
Formula & constants
Concrete is ordered by the cubic yard: length × width × (thickness ÷ 12) ÷ 27. One cubic yard equals about 45 bags of 80 lb mix. Add 5–10% for uneven subgrade. Every default in the fields above is editable — when your supplier’s spec sheet lists a different density, coverage rate or price, enter that number instead. The waste and compaction allowances follow common trade practice; see our methodology page for the derivation of each formula and the standards it references.
≈ 1 ready-mix truck — bags stop making sense above ~1 cu yd.
Where this fits in the project
Concrete work starts below grade: excavation, then a compacted gravel base for drainage, formwork, rebar where the slab spec requires it, then the pour. Order by cubic yard and round up — a short load fee costs more than surplus material.
How this connects to your project
No quantity stands alone — each material in the chain depends on the ones around it. These are the planning steps that pair with the concrete calculator:
- Concrete Slab Calculator — Concrete calculator covers all shapes; slab is specific to flatwork.
- Concrete Cost Calculator — Once you know yardage, estimate total concrete cost.
- Concrete Bag Calculator — For small projects, calculate bagged concrete instead of ready mix.
- Concrete Footing Calculator — Footings require concrete volume calculation.
- Concrete Block Calculator — Poured concrete vs CMU block wall comparison.
- Rebar Calculator — Concrete typically requires steel rebar reinforcement.
- Concrete Column Calculator — Columns are vertical concrete elements.
- Ready Mix Calculator — Large pours use ready mix trucks, not bags.
- Asphalt Calculator — Concrete and asphalt are competing paving materials.
- Gravel Calculator — Concrete is approximately 60-75% aggregate by volume.
- Sand Calculator — Sand is the fine aggregate component in concrete.
- Excavation Calculator — Excavate before pouring concrete footings or slabs.
- Compaction Calculator — Subgrade must be compacted before concrete placement.
- Stair Calculator — Concrete stairs require volume calculation.
Frequently asked questions
How many 80 lb bags per cubic yard?
45 bags of 80 lb mix (each yields 0.6 cu ft). Above one yard, ready-mix delivery beats bagged on cost and quality.
How thick should a concrete slab be?
4 in for patios and walks, 6 in for driveways, 6–8 in with reinforcement where trucks load it.
Do I add extra when ordering?
Yes — 5–10% over calculated volume covers subgrade irregularity and spillage; a short-load fee costs more than the surplus.
Last verified: — prices reflect current national averages. See our methodology.
Estimates are for planning. Material densities, coverage rates and prices vary by region and supplier — confirm final quantities before ordering, and check local code where structural or electrical work is involved.