Concrete Calculator: Slab Volume, Cubic Yards and Bags

Calculate your quantities

Enter your measurements below. Change the example allowance, product information and price to match your project.

Enter measurements and select Calculate.

Prices use your chosen currency. A zero price leaves cost at zero. Material estimates exclude labor, tax, delivery and accessories. Enter decimal feet, not feet-and-inches notation. Decimal point or comma accepted; omit thousands separators.

How to use this concrete calculator

Use the finished slab dimensions. Bag yield is the mixed volume printed by the manufacturer, not dry bag weight. The example yield and allowance are editable assumptions. Estimates quantities only; reinforcement, structural thickness and mix design require separate decisions.

Measure the relevant area or volume using the units shown beside each input.
Replace example product values with the supplier's yield, coverage, density or pack quantity where applicable.
Set the extra allowance explicitly. Enter zero when you want the geometric quantity without an allowance.
Select Calculate, then compare the unrounded purchasing basis with whole bags, boxes or packs where displayed.

Formula

Volume in ft³ = length × width × thickness / 12. Order volume = volume × (1 + extra / 100). Cubic yards = ft³ / 27. Bags = order ft³ / yield per bag, rounded up.

Worked example

A 10 × 10 ft slab, 4 in thick, has 33.333 ft³ of geometric volume. With 10% extra, order volume is 36.667 ft³ = 1.358 yd³. At an entered yield of 0.6 ft³/bag, round up to 62 bags.

Six calculated examples

Only the first length changes in this table. All other inputs use the calculator's reset values shown above. These are mathematical scenarios, not measured supplier quotes.

concrete quantity examples
First length	Calculated quantities
5 ft	Geometric volume (ft³): 16.667; Order volume (ft³): 18.333; Order volume (yd³): 0.679; Order volume (m³): 0.519; Bags: 31
8 ft	Geometric volume (ft³): 26.667; Order volume (ft³): 29.333; Order volume (yd³): 1.086; Order volume (m³): 0.831; Bags: 49
10 ft	Geometric volume (ft³): 33.333; Order volume (ft³): 36.667; Order volume (yd³): 1.358; Order volume (m³): 1.038; Bags: 62
12 ft	Geometric volume (ft³): 40; Order volume (ft³): 44; Order volume (yd³): 1.63; Order volume (m³): 1.246; Bags: 74
15 ft	Geometric volume (ft³): 50; Order volume (ft³): 55; Order volume (yd³): 2.037; Order volume (m³): 1.557; Bags: 92
20 ft	Geometric volume (ft³): 66.667; Order volume (ft³): 73.333; Order volume (yd³): 2.716; Order volume (m³): 2.077; Bags: 123

Frequently asked questions

Does this design my slab?

No. It estimates material for dimensions you supply; it does not determine load capacity or reinforcement.

Can I use it for footings?

Yes, for rectangular segments with supplied dimensions. Calculate each segment separately without counting overlaps twice.

Does cost include delivery?

No. It multiplies entered volume price by order volume. Minimum-order, delivery, labor and tax charges are additional.

Units and calculation limits

One foot is 0.3048 meters; one cubic yard is 27 cubic feet. Calculations retain precision until display; whole-package quantities are rounded up. Outputs estimate quantities from your measurements and assumptions. Confirm product coverage and units before ordering.