Ready mix concrete calculator

A 6x3m driveway 100mm thick is 1.8 m³ of concrete (1.89 m³ with 5% extra). Adding 10% and rounding up to the next 0.2 m³, order 2 m³ of ready-mix. A 20x10ft driveway at 4in rounds up to 2.75 yd³.

1. What are you doing?

2. Shape

Then tap a size on the picture to type it.

3. Your job

Tap a size to type it. Use Plan to drag the corners or draw your own shape.

4. Sizes

Length (m)

Width (m)

Depth (mm)

Sloped (deeper at one end)

Extra allowed (%)

Allmat concrete calculator

You need 1.89 m³ of concrete

1.8 m³ plus extra for spillage and uneven ground (5% on the driveway).

Order a ready-mix truck

If you order ready-mix, ask for about 2 m³. That adds 10% and rounds up to the next step a supplier sells.

Details: other bag sizes, water, weight, getting it home

From bags this would be 208 x 20kg PROSTRENGTH Extra Strength Concrete 20kg, but at this size the truck is the sensible order.

Cement Australia's guide: under 0.1 m³ use bags, 0.1 to 0.5 m³ mix your own, over 0.5 m³ ready-mix. Up to about 1 m³ we still show the bags; past that, and for a house slab or a driveway beyond a small patch, it is a truck pour.

How we worked it out

Driveway: 1.8 m³ plus 5% = 1.89 m³, ordered as ready-mix.

Cement Australia: about 110 x 20kg bags make 1 m³ (their FAQ, calculator and the PROSTRENGTH Rapid Set data sheet). Rapid Set Concrete publishes no per-m³ figure, so it uses the same 110.

Trade Mortar: about 20 house bricks or 10 masonry blocks per 20kg bag at a 10mm joint (Cement Australia).

Estimates only. Check sizes and quantities against your plans, and with your engineer or builder, before you order.

Pour-day check

Type in the weather for the day you plan to pour. Temperature never changes how much you need; it changes the timing.

Air temp (°C)

Wind (km/h)

Humidity (%)

PROSTRENGTH Extra Strength Concrete 20kg: 20°C is within the maker's range (5°C to 35°C).
Ready-mix (house slab or driveway): AS 1379 requires the concrete to arrive between 5°C and 35°C; outside that, talk to the plant (CCAA).
Keep it damp for 7 days (Cement Australia).

Embed this calculator

Put the Allmat concrete calculator on your own site. Copy this code into your page.

Opens on

Compact: no job tiles, just this job and the answer

<iframe id="allmat-calc" src="https://allmat.com.au/embed/concrete-calculator?job=ready-mix" width="100%" height="1600" style="border:0;max-width:100%" loading="lazy" title="Concrete calculator by Allmat"></iframe>
<script>window.addEventListener('message',function(e){var f=document.getElementById('allmat-calc');if(f&&e.source===f.contentWindow&&e.origin==='https://allmat.com.au'&&e.data&&e.data.type==='allmat-calc-height'){f.style.height=e.data.height+'px'}})</script>
<p><a href="https://allmat.com.au/concrete-calculator" rel="nofollow">Concrete calculator by Allmat</a></p>

The frame sizes itself to the calculator; the small script handles that. The link under the frame can stay or go.

How much ready mix concrete do I need?

Work out the volume, add about 10% for the ground and the formwork, then round up to what the supplier sells. In Australia ready-mix is ordered in 0.2 m³ steps; in the US it is usually quarter-yard steps.

Small loads often carry a minimum charge, so ask your supplier before you book a part load.

Bags or a ready-mix truck?

Cement Australia's guide sets the line by job size:

Bags or a truck? Cement Australia's guide by job size
Job size	In cubic yards	What to use
Under 0.1 m³	under 0.13 yd³	Bags of concrete mix
0.1 to 0.5 m³	0.13 to 0.65 yd³	Bags, or mix your own with Builders Cement, sand and aggregate
Over 0.5 m³	over 0.65 yd³	Ready-mix delivered, where access allows

Cement Australia, "How to lay a concrete slab". Cubic yard figures are our conversion. The calculator shows bags up to about 1 m³ and a truck past that; house slabs, and driveways beyond a small patch, are truck pours.

How many bags of concrete in a yard or a cubic metre?

A cubic yard of concrete takes about 46 x 80lb bags, and a cubic metre about 110 x 20kg bags of Cement Australia mix. The reference page has every bag size.

Before the truck arrives

Can the truck get within reach of the pour, or will you need a pump or barrows?
Is the formwork braced and the base compacted?
Do you have enough people to place and finish the load before it stiffens?

Questions

Length × width × depth gives the volume. Add about 10% and round up to the next 0.2 m³ (or quarter yard) that the supplier sells.

About 46 bags of 80lb, or roughly 84 bags of 20kg, make one cubic yard, using our estimate from bag weight.

Cement Australia's guide: over about 0.5 m³, where a truck can get access, have pre-mixed concrete delivered.

Many do, so a part load can cost more per cubic metre. The calculator shows the volume; ask your supplier how they price a small load.

Goes with this job

Disclaimer

This calculator gives estimates from the sizes you enter, using manufacturers' published figures and standard geometry. It is not engineering or design advice. Footing, slab and beam sizes must come from your plans or engineer. Allow for site conditions, spillage and uneven ground. Check quantities with your supplier before ordering. Allmat accepts no responsibility for decisions made using these estimates.

Sources

Cement Australia: how to lay a concrete slab
Cement Australia: frequently asked questions
Allmat arithmetic (this calculator)

Last checked 5 October 2026.

Cite this page

Allmat, "Ready mix concrete calculator", https://allmat.com.au/concrete-calculator/ready-mix, checked 5 October 2026.