Concrete & Material Quantity Calculator

Measure the length, the width and the finished thickness or depth. Matching pieces - four identical pad footings, say - are one set of measurements with a quantity of four. Split an L-shaped or irregular slab into rectangles and add them up, or find its area first with the Square Footage Calculator.

A round shape needs a diameter - the distance straight across, twice the radius - and one other measurement: thickness for a slab, height for a column, depth for a footing. The units differ by shape, and the form shows the unit beside each field.

The waste allowance is applied once, and all three workflows start from the same adjusted volume. Bag counts are rounded up, because you can't buy part of a bag. Volumes are shown in cubic feet, cubic yards and cubic meters using exact NIST conversions (1 yd³ = 27 ft³; 1 ft³ = 0.028316846592 m³; 1 lb = 0.45359237 kg).

Displayed volumes are rounded so they are easy to read, but a cost is worked out from the full-precision volume, not the rounded figure shown. That is why multiplying the rounded 3.24 yd³ by USD 150.00 per cubic yard gives USD 486.00, while the calculator shows USD 486.11.

A nominal mix such as 1 : 2 : 4 is one part cement, two parts sand and four parts coarse aggregate by volume - seven parts in all, so cement is 1/7 of the dry materials, sand 2/7 and aggregate 4/7. Nominal ratios are rules of thumb; they do not guarantee a particular strength. For structural work, use the mix your drawings or engineer specify - structural concrete is normally proportioned by a mix-design procedure and adjusted from trial batches, as described in ACI PRC-211.1.

When you mix concrete yourself you buy the ingredients loose, and loose cement, sand and aggregate take up more room than the finished concrete: there are air gaps between the particles, damp sand bulks up, and a little is lost in handling. The dry-volume factor scales your concrete volume up to the volume of loose ingredients to buy. A factor of 1.54 is widely used for rough nominal-mix estimates; it is an estimating convention, not a published constant, so use your own figure if you have one.

It applies only to site mixing. Ready-mix is ordered by the volume of finished concrete, and a pre-mixed bag's published yield already describes finished concrete, so neither workflow uses it.

The mix ratio gives cement as a volume, but cement is sold by weight, so the volume is converted with its loose bulk density - the weight of a container of loose powder, air gaps included. 1,440 kg/m³ is a commonly quoted estimating value, and the real figure varies with how settled the powder is. Do not use cement's particle (absolute) density from mix-design tables here: it leaves out the air between particles, is much higher, and would overstate the cement you need.

The mix ratio is by volume, but the water-cement ratio is a ratio of masses (weights). ACI describes it as the mass of mixing water divided by the mass of cementitious material; cement is the only binder here, so it is water ÷ cement. A ratio of 0.5 means half a kilogram of water for each kilogram of cement (about half a liter). The optional water estimate is cement weight × water-cement ratio. Damp sand and aggregate already carry water, which mix-design procedures adjust for, so follow the water quantity in your specification rather than adding the full estimate on top.

Ready-mix is ordered by the volume of finished concrete - typically cubic yards in the US and cubic meters in metric countries - so the order is simply your adjusted volume. Divide cubic feet by 27 for cubic yards. Do not apply the site-mix dry-volume factor: the supplier batches the dry materials, and at 1.54 the factor would overstate your order by about half.

The calculator does not round your order up to a quarter yard or any other step, because suppliers differ. Ask yours about minimum loads, short-load charges and the increment they batch in.

A bag of concrete mix already contains the cement, sand and stone - you add water. Each manufacturer publishes a yield for each bag size: the volume of concrete one bag makes. Treat it as an estimating value for that product and bag size. The calculator divides your volume by that yield and rounds up. No dry-volume factor, mix ratio or cement density is involved.

The listed products are specific QUIKRETE and SAKRETE mixes sold in the US in pound bags. If your bags are 20 kg, 25 kg or any other size, or a fast-setting, high-early-strength or lightweight mix, choose a custom yield and enter the figure the manufacturer publishes for that bag - in liters per bag with Metric selected. Do not work a yield out from the bag weight: mixes of the same weight can yield different volumes.

A cement bag holds only cement and belongs with the Site-mixed workflow, where you buy sand and aggregate separately. A bag of concrete mix holds everything and is counted by its yield. The calculator keeps their counts, labels and prices separate.

A pour rarely uses exactly the calculated volume. An uneven or soft base, forms that bow, spillage and concrete left in the mixer or pump all add to it. There is no single correct percentage, so choose one for your site or ask your supplier or contractor. The calculator adds it once; leave the field blank for none.

On the reference slab, a 5% allowance turns 83.33 ft³ (3.09 yd³) into 87.5 ft³ (3.24 yd³, 2.478 m³).

This is a quantity estimate from the measurements and assumptions you enter. Real quantities also depend on the mix design, moisture in the sand and aggregate, how the concrete is batched and compacted, and how accurately the forms are set. Strength depends on the mix design, the water-cement ratio - which FHWA describes as the main control of compressive strength, abrasion resistance and permeability - and on placing and curing.