Concrete Slab Calculator: Bags, Yards & Cost

A 10 × 10 ft slab 4 in thick is 33.3 cu ft (1.23 cu yd): 56 bags of 80 lb Quikrete Concrete Mix, 75 bags of 60 lb, or 37 bags of 80 lb Sakrete Maximizer, before any margin. Type your own size and prices below for bags vs a ready-mix truck.

Set up for: a slab, pad or patio · Different project?

Common slab sizes

Slab	Cu yd, 4 in	80 lb bags, 4 in	Cu yd, 6 in	80 lb bags, 6 in
10 × 10 ft	1.23	56	1.85	84
12 × 12 ft	1.78	80	2.67	120
20 × 20 ft	4.94	223	7.41	334
8 × 8 ft	0.79	36	1.19	54
10 × 12 ft	1.48	67	2.22	100
30 × 30 ft	11.1	500	16.7	750
8 × 10 ft	0.99	45	1.48	67
12 × 24 ft	3.56	160	5.33	240
12 × 36 ft	5.33	240	8.00	360
20 × 30 ft	7.41	334	11.1	500
20 × 40 ft	9.88	445	14.8	667

80 lb Quikrete Concrete Mix at 0.60 cu ft per bag, whole bags, no margin. Thickness is your choice from your plans; we don't recommend one.

FAQ

How do I work out the cost of a concrete slab?

Multiply the bag count by your store's price per bag, or the cubic yards plus a 4–10% margin by your ready-mix plant's price per yard, then add its delivery and short-load fees. Type those prices into the calculator and it shows both totals side by side. We publish no prices because they change by store and region.

How many bags of concrete for a slab?

Bags = length × width × thickness (in) ÷ 12 ÷ the yield per bag, rounded up. Quikrete's own calculator uses the same formula; yields differ by product, so the calculator lists every mix we track.

How do I check a contractor's quote?

Enter the slab size and the yards on the quote. The calculator compares them with the computed volume and with NRMCA's 4–10% over-order guidance.

Sources

Quikrete: QUIKRETE Concrete Mix (No. 1101) data sheet · fetched and reviewed 2026-11-10
Quikrete: QUIKRETE Concrete Mix SPEC-DATA sheet · fetched and reviewed 2026-11-10
Quikrete: QUIKRETE online project calculator (calculator.js) · fetched and reviewed 2026-11-10
Quikrete: QUIKRETE Fast-Setting Concrete Mix (No. 1004-50) data sheet · fetched and reviewed 2026-11-10
Sakrete: Sakrete High Strength Concrete Mix technical data sheet · fetched and reviewed 2026-11-10
Sakrete: Sakrete 5000 Plus Concrete Mix technical data sheet · fetched and reviewed 2026-11-10
Sakrete: Sakrete Maximizer Concrete Mix technical data sheet · fetched and reviewed 2026-11-10
NRMCA: CIP 31: Ordering Ready Mixed Concrete · fetched and reviewed 2026-11-10

Bags vs ready-mix · How much extra to order · Water per bag

Volumes only. ConcreteMath calculates volumes, bag counts, weights and your own cost figures. It gives no structural or engineering advice and never sizes footings, piers, slabs or rebar: those come from your plans, an engineer or your local building department. Bag counts are estimates from each maker's published yield; actual use varies with hole shape, uneven ground, waste and mixing. Bulk weights are published ranges; your supplier's figure wins.