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Concrete slab cost calculator: bags vs ready-mix
Compare the material cost of bagged concrete and ready-mix for a slab in Australia, the UK or Canada using your current local prices.
Your result
Your plan starts
with a few details.
Enter your project measurements and product details, then calculate to see an estimated take-off.
How it works
Enter slab dimensions, the allowance you choose, bag yield, the price per bag, ready-mix price per cubic metre and any delivery or small-load fee. The page uses Australian dollars, pounds sterling or Canadian dollars according to the country route.
The calculator compares whole bag cost against ready-mix volume cost plus the entered fee. The switch point compares continuous rates and does not account for whole-bag rounding.
Formula
Calculate quantity
Slab volume = length × width × thickness Order volume = slab volume × (1 + allowance %) Bag count = ceil(order volume ÷ maker yield per bag)Convert thickness from millimetres to metres. Bag yield and prices are entered from your chosen supplier.
Compare material costs
Bag cost = whole bag count × price per bag Ready-mix cost = order volume × price per m³ + delivery fee Switch point = delivery fee ÷ (bag price ÷ bag yield − ready-mix price per m³)A continuous switch point is shown only when the per-volume bag rate is higher than the ready-mix rate.
Worked example
For a 3 m × 3 m slab at 100 mm thick, volume is 0.9 m³. At an entered 0.01 m³ yield per bag and a 5% allowance, order volume is 0.945 m³ and the bag estimate is ceil(0.945 ÷ 0.01) = 95 bags. Enter current supplier prices to compare costs. These yield and dimensions illustrate the formula, they are not a sourced product recommendation.
Assumptions and limits
Australia’s ABS, the UK government and Statistics Canada publish construction-price data or indices, but those series are not direct local supplier quotes for a small slab. The estimate uses the prices and bag yield you enter. Compare quotes with the same tax, delivery, minimum-load, pumping and placement assumptions.
The tool compares material costs only. It does not include labour, formwork, reinforcement, pumping, disposal or supplier minimum order quantities unless you include them in the entered figures.
Frequently asked questions
Are the displayed prices live?
No. Enter current supplier prices for your postcode or delivery area. The sources explain broad national price statistics, not live retail prices.
What does the switch point mean?
It is the order volume where continuous bag cost per cubic metre and ready-mix cost plus your delivery fee are equal. Whole bags can move the actual comparison around that point.
Why can actual bag cost differ from the continuous switch point?
Bags are purchased as whole packs, while the switch point compares continuous costs per cubic metre. A small change in volume can add a whole bag without changing the quoted ready-mix unit rate.
Which charges should I compare in supplier quotes?
Use the same tax basis and check delivery, minimum loads, small-load fees, pumping, waiting time and placement. Include only comparable costs in the inputs; labour and reinforcement are separate unless explicitly included.
Sources
Specs as of: