Concrete Calculator Guide

What This Calculator Does

The Concrete Calculator estimates mixed volume for slabs, cylinders or a known area with depth. Combine up to 10 regions, add a material allowance and convert volume to cubic feet, cubic yards and cubic metres. Whole bags use the mixed yield you enter; optional prices add a material budget.

When to Use It

Use it for uniform slabs or complete cylindrical pours. Cylinder mode uses diameter and depth. For a post hole already occupied by a post, supply a separately measured net area: the tool does not infer an annular gap. Measure footprints with square footage, or estimate aggregate with gravel.

Inputs Explained

US inputs use feet for lengths and diameter, inches for depth, and square feet for known area. Metric inputs use metres, centimetres and square metres respectively. Active dimensions must be positive, at most 1e12. Allowance is 0–100%. Enter the bag’s mixed yield in ft³, litres or m³. Prices are optional, non-negative and use one selected currency label.

How the Calculation Works

Rectangle area = length×width. Circle area = π×(diameter/2)². Base volume = sum of area×depth. Adjusted volume = base×(1+allowance/100). Bags = ceiling(adjusted volume/bag yield). Unit factors: 1 ft = 0.3048 m; 1 in = 0.0254 m; 1 ft³ = 0.028316846592 m³; 1 yd³ = 0.764554857984 m³.

Example

A 12 ft×10 ft slab at 4 in thick has volume 12×10×(4/12)=40 ft³, about 1.481481 yd³ or 1.132674 m³. With no allowance and an illustrative mixed yield of 0.6 ft³ per bag, 40/0.6=66.666667, so buy 67 whole bags. At an example 8 currency units per bag the material cost is 536; this is not a market quote.

How to Understand the Result

The main volume includes allowance. Base volume excludes it. Purchased bag volume can exceed the needed volume because bags round up. Bag cost uses whole bags; bulk cost uses unrounded adjusted volume, priced per yd³ in US mode or per m³ in metric mode. Unit switches convert valid dimensions and the bulk-price basis. Bag units remain independently selected.

Common Mistakes

Do not infer mixed yield from package weight: 80 lb is mass, not a volume. Verify the exact product yield, not just its bag weight. Enter diameter rather than radius, and keep thickness units distinct from footprint units. Currency selection labels values without exchanging them.

FAQ

Why round the bags up?

Whole bags must cover the allowance-adjusted quantity.

Is 0.6 ft³ universal for an 80 lb bag?

No. It is an editable example; check the specific product’s data sheet.

Does this design a structural slab?

No. It estimates material quantities only.

Notes

The QUIKRETE Concrete Mix product page links product-specific data sheets; no brand or strength is selected automatically here. No structural design, reinforcing steel, pump residue, labor, delivery or tax is included. Region volume is bounded at 1e−12 to 1e12 m³; total volume cannot exceed 1e12 m³, bag count 1e9, or cost 1e15. Inputs stay in page state.