Estimate concrete volume and bags in minutes. Whether you are pouring a slab, footing, column, or a set of stairs, this Concrete Calculator turns dimensions into dependable numbers you can take to the store or send to your contractor.
Why use a Concrete Calculator?
Concrete is heavy, permanent, and unforgiving. Ordering too little halts your project; ordering too much wastes money and space. A Concrete Calculator removes guesswork by translating your project’s shape and size into volume, then into the number of premixed bags or ready-mix yardage you need. It also helps you build a prudent overage to cover spillage, uneven sub-base, and small measurement errors.
What the calculator covers
- Slabs and pads: driveways, patios, sheds, and garage floors.
- Footings and trenches: perimeter and isolated footings for walls, posts, and fences.
- Columns and cylinders: sonotube piers, round posts, or bollards.
- Monolithic stairs: straight-run steps cast in place.
Units: Imperial or Metric
Choose Imperial (feet and inches) or Metric (meters and centimeters). In Imperial, the calculator uses feet for length/width and inches for thickness or rise/run. In Metric, it uses meters for length/width and centimeters for thickness or rise/run. Volumes are returned in cubic yards, cubic feet, and cubic meters so you can compare quotes from premix suppliers and ready-mix plants.
Formulas used
- Slab/Rectangle: length × width × thickness
- Footing/Trench: length × width × depth
- Column/Cylinder: ? × r2 × height
- Stairs (monolithic): width × (n × rise) × (n × run) ÷ 2
After computing the net volume, the Concrete Calculator applies your waste percentage, typically 5–10% for well-prepared sites and up to 15% for complex pours or rough subgrades.
How to measure accurately
- Measure two ways: Use a tape and a laser if possible. Average small irregularities.
- Check square: For slabs, confirm diagonals match to avoid skewed corners.
- Account for slopes: Measure the thickest edge if the slab is sloped or variable.
- Compact the base: A well-compacted sub-base reduces surprise overages.
- Round up bags: You can return unused bags, but you can’t return to finish a pour.
Bag yields and ready-mix
Premixed bag yields vary by brand and moisture. Typical yields are about 0.30, 0.375, 0.45, and 0.60 cubic feet for 40, 50, 60, and 80 lb bags, respectively. For metric bags, 20, 25, and 30 kg often yield around 0.009, 0.012, and 0.014 cubic meters. The calculator uses these typical values to estimate bag counts. For truck deliveries, most plants sell by cubic yard (yd³); order slightly more than the computed total to avoid a cold joint.
Best practices for ordering
- Choose mix strength: 3000–4000 psi (20–28 MPa) is common for slabs; ask your inspector if required.
- Add fibers or air entrainment if your climate or design calls for it.
- Plan logistics: staging, wheelbarrows or pump, and curing blankets if cold.
- Have tools ready: screed, bull float, trowels, and curing compound.
Frequently avoided pitfalls
Underestimating thickness, forgetting perimeter thickening, or excluding steps and edge turn-downs can short your order. Likewise, rough sub-bases and unbraced formwork create bulges that add volume. Verify dimensions against drawings and consider a separate calculation for thickened edges.
From volume to success
With accurate dimensions and a reasonable waste factor, the Concrete Calculator gives you a realistic order quantity. It transforms raw measurements into a clear plan—bags to buy or cubic yards to schedule—so your pour starts and finishes smoothly. Measure carefully, double-check entries, and you’ll pour with confidence.