Reference formulas and worked examples below keep their stated units. Monetary examples use USD; dimensional examples use US customary units unless labeled otherwise. Metric calculator inputs are converted to these reference units before calculation. Choosing another currency does not convert example amounts or exchange money.
How to use this concrete slab cost calculator
Choose a rectangular or round slab and enter its dimensions. Open the two quote sections to set your bag yield, prices, delivery terms, and labor. All starting prices are editable examples.
How the calculation works
Rectangular area = length × width; round area = π × (diameter ÷ 2)². Multiply by matching slabs, thickness, and (1 + waste percentage ÷ 100) to find required concrete volume.
Whole bags = required volume ÷ the entered mixed yield, rounded up. Bag material cost = whole bags × price per bag.
Billed ready-mix volume = the greater of required volume and minimum billed volume, rounded up to the supplier’s order increment. Price per cubic meter or cubic yard is applied in the selected unit.
For each option, add its material, delivery, and labor amounts plus shared other costs. Multiply this subtotal by (1 + tax rate ÷ 100). The lower result uses only the entered costs.
Worked example
A 10 × 10 ft slab, 4 in thick, with 10% extra needs 36.6667 cu ft. At 0.6 cu ft yield and $7 per bag, buy 62 bags for $434. With a 1 cu yd minimum and 0.25 cu yd increments, ready-mix bills 1.5 cu yd. At $160/cu yd plus $100 delivery, it costs $340. With no other costs or tax, ready-mix is $94 lower.
Limits and assumptions
A quantity and quote comparison, not structural design or a live price service. No automatic reinforcement, excavation, pump, strength specification, labor productivity, or regional tax calculation. Enter those costs explicitly when relevant. Bags are rounded up; ready-mix minimums and increments may exceed the volume used. Supplier pricing units remain explicit when measurement preferences change.
Frequently asked questions
Why can ready-mix billed volume exceed what I need?
The supplier may bill a minimum load and sell in volume increments. Both are editable, and the result shows the billed quantity separately from the slab requirement.
Can I use metric measurements and a price per cubic meter?
Yes. Select Metric in Currency & units and choose Price per cubic meter in the ready-mix quote. Measurement switching converts dimensions; it does not silently change a quoted price unit.
Does changing currency convert the quote?
No. The currency labels change, while the amounts stay as entered. Use one currency consistently for the comparison.
Does the lowest material price always win?
No. Whole bags, delivery minimums, fees, and different labor costs can change the total. Enter each option’s complete quote before comparing.
Is the default thickness suitable for my project?
The thickness is an editable example. This calculator does not select safe structural thickness, reinforcement, or a mix specification.
References
QUIKRETE Concrete Mix #1101: manufacturer bag-yield specifications