How much concrete do you need for a 12×24 slab?

A 12×24 ft slab poured 4 inches thick needs 3.56 cubic yards (96 cu ft) of concrete. With 10% extra for waste, buy 176 bags of 80 lb premix or order 3.91 yards of ready-mix.

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Your results

Concrete to buy (incl. 10% extra)3.91 cu yd
80 lb bags176
60 lb bags235
40 lb bags352
Exact volume96 cu ft (3.56 cu yd)
How much concrete do you need for a 12×24 slab — diagram

Concrete for a 12×24 slab at different thicknesses

The slab covers 288 square feet. Every extra inch of thickness adds about 0.89 cubic yards. Quantities below include 10% for waste.

ThicknessCubic yards80 lb bags60 lb bags40 lb bags
3.5 in3.42154206308
4 in3.91176235352
5 in4.89220294440
6 in5.87264352528
8 in7.82352470704

Bags or ready-mix for this size?

At 3.91 cubic yards, bags mean mixing 176 bags weighing roughly 7 tons. Ready-mix delivery is usually the practical choice at this size, and it gives a more consistent slab.

How heavy is a 12×24 slab?

Normal-weight concrete weighs about 150 lb per cubic foot, so a 4-inch 12×24 slab weighs roughly 14,400 lb (7.2 tons) once cured. Make sure your base is compacted gravel on firm, undisturbed soil.

The math

12 ft × 24 ft × (4 in ÷ 12) = 96 cu ft 96 cu ft ÷ 27 = 3.556 cu yd +10% waste = 105.6 cu ft 105.6 ÷ 0.6 cu ft per 80 lb bag = 176 bags (rounded up)

Common questions

How many 80 lb bags of concrete for a 12x24 slab?

176 bags for a 4-inch slab including 10% extra (160 with no extra). At 6 inches thick you need 264 bags.

How many yards of concrete for a 12x24 slab 6 inches thick?

5.87 cubic yards including 10% extra, or 5.33 yards exactly.

How many 60 lb bags for a 12x24 slab?

235 bags of 60 lb concrete for a 4-inch slab with 10% extra.

Want the full method, tips and other sizes? See the concrete calculator guide.

Last reviewed November 1, 2026. Results are estimates — confirm with your supplier.

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