Concrete Calculator
Estimate concrete for slabs and other common pours with waste, whole-bag counts and ready-mix rounding, plus optional material cost and weight.| Measure | Estimate | Order context | Copy |
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Pour guidance
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Concrete ordering begins with the space inside the forms or excavation. Length, width, diameter, and filled depth determine the geometric volume; an allowance is then added for uneven subgrade, form variation, spillage, and measurement uncertainty. Supplier ticket increments and packaged-mix yields turn that volume into an order quantity.
A volume estimate is not a structural design. Slab thickness, footing size, reinforcement, joints, base preparation, frost depth, soil bearing, and concrete specification must come from appropriate drawings, code requirements, or professional advice. Measuring the wrong boundary precisely still produces the wrong order.
| Pour | Measure | Watch for |
|---|---|---|
| Slab or pad | Inside length, inside width, finished thickness | Thickened edges, slopes, depressions, and irregular base |
| Footing or trench | Concrete-filled length, width, and depth | Excavation clearance that will not be filled |
| Round pier or hole | Inside diameter and concrete-filled depth | Flared bottoms and collapsed or oversized holes |
| Known volume | Existing takeoff volume | Whether waste or repeated sections are already included |
Small jobs may suit packaged mix, while larger placements often favor ready-mix delivery. The crossover depends on labor, mixer capacity, truck access, placement time, supplier minimums, short-load charges, and delivery fees. Material-only prices do not capture those job constraints.
How to Use This Tool:
Measure one representative pour, choose its shape, and keep every dimension paired with the correct unit.
- Select Slab or pad, Footing or trench, Round pier or post hole, or Known-volume takeoff. Enter a whole-number count for repeated identical pours.
- Enter the dimensions requested for that shape. Use clear inside form dimensions and the concrete-filled depth; for a known-volume takeoff, enter the volume before this tool's waste allowance.
- Set the Waste allowance from 0% to 40%. Confirm that the source takeoff has not already included the same allowance.
- Choose the ready-mix ticket unit and supplier rounding increment, then select the packaged-mix bag size whose count you want in the summary.
- Review Concrete takeoff and Pour guidance. Add optional prices or density only when you have job-specific values; zero leaves cost or weight out of the result.
Interpreting Results:
Waste-adjusted volume is the common quantity used for both packaged-mix and ready-mix estimates. Bag counts always round upward to whole bags. A ready-mix ticket rounds upward only when a 0.25, 0.5, or 1-unit increment is selected.
- Bag-friendly, Small-pour quote, Compare both, and Ready-mix likely are planning cues based on cubic yards, not supplier rules or labor estimates.
- Ready-mix ticket may exceed the geometric estimate because of waste and ticket rounding. Ask the supplier which increments and minimums are accepted.
- Bag yields are approximate published yields. Product, water addition, consolidation, and placement loss can change actual coverage.
- Optional costs cover only selected bag price or ready-mix unit price. Delivery, short-load, pumping, tax, labor, equipment, and unused material are excluded.
Technical Details:
All lengths are converted to meters and all volumes to cubic meters before geometry, waste, ordering, and optional weight calculations. Full precision is retained through the model; displayed cubic meters, cubic yards, bag counts, and costs are formatted only after the result is calculated.
Formula Core
Rectangular pours use prism volume. Round pours use cylinder volume. The identical-pour count n multiplies one measured shape.
The waste allowance is applied once to base volume. Packaged-mix and ready-mix quantities both derive from that adjusted result.
For ticket increment q, ready-mix volume is rounded upward to the next multiple of q. With no ticket rounding, the adjusted volume is kept exactly.
Bag cost equals whole bags multiplied by price per bag. Ready-mix cost equals the ticket quantity in the selected supplier unit multiplied by that unit price. Optional concrete weight equals adjusted cubic meters multiplied by the entered density.
Lookup Core
| Bag size | Approximate yield |
|---|---|
| 40 lb / 18.1 kg | 0.30 ft³ |
| 50 lb / 22.6 kg | 0.375 ft³ |
| 60 lb / 27.2 kg | 0.45 ft³ |
| 80 lb / 36.2 kg | 0.60 ft³ |
Exact conversion factors include 1 ft³ = 0.028316846592 m³ and 1 yd³ = 0.764554857984 m³. Length units cover millimeters, centimeters, meters, inches, feet, and yards; known volume accepts liters, cubic meters, cubic feet, or cubic yards.
Rule Core
| Rule | Boundary | Planning label |
|---|---|---|
| Order lane | Final volume < 0.5 yd³ | Bag-friendly |
| Order lane | 0.5 yd³ ≤ volume < 1 yd³ | Small-pour quote |
| Order lane | 1 yd³ ≤ volume ≤ 2 yd³ | Compare both |
| Order lane | Final volume > 2 yd³ | Ready-mix likely |
| Waste check | Below 5%; 5% to 15%; above 15% | Low; typical; high |
| Slab depth | Below 3.5 in; 3.5 in to 6 in; above 6 in | Review; common planning band; heavy |
| Footing depth | Below 6 in; at least 6 in | Review; captured |
| Ready-mix ticket | Below 1 yd³; 1 yd³ to 10 yd³; above 10 yd³ | Short load; quote ready; truck planning |
These thresholds drive guidance only. They do not prescribe structural depth, supplier capacity, truck count, minimum order, or the correct waste percentage for a job.
Limitations:
- Irregular excavations, thickened edges, slopes, steps, penetrations, and variable depth need separate measurements or a more detailed takeoff.
- Packaged-mix yields are approximate product values and may not represent another mix.
- Ready-mix quantity does not determine mix design, strength, slump, air content, aggregate size, admixtures, or placement schedule.
- Price comparisons exclude delivery, short-load, pumping, tax, labor, equipment, and scheduling costs.
- Optional weight is only as accurate as the density entered and is not a lifting, transport, or structural load calculation.
Worked Examples:
Metric slab with a ten-percent allowance
A 3.6 m by 3.0 m slab at 0.10 m thick has a base volume of 1.08 m³. Adding 10% gives 1.188 m³, or about 41.96 ft³ and 1.55 yd³. At the published 0.60 ft³ yield, the exact requirement is about 69.92 of the 80 lb bags, so the order rounds up to 70 bags. Ready-mix ticket rounding, if selected, is applied after the 1.188 m³ estimate.
References:
- Guide for the Use of the International System of Units, National Institute of Standards and Technology.
- Concrete Mix Product No. 1101 Data Sheet, The QUIKRETE Companies.
- CIP 31: Ordering Ready Mixed Concrete, National Ready Mixed Concrete Association.