How much concrete do you need for an 8×8 slab?

A 8×8 ft slab poured 4 inches thick needs 0.79 cubic yards (21.3 cu ft) of concrete. With 10% extra for waste, buy 40 bags of 80 lb premix or order 0.87 yards of ready-mix.

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Your results

Concrete to buy (incl. 10% extra)0.87 cu yd
80 lb bags40
60 lb bags53
40 lb bags79
Exact volume21.33 cu ft (0.79 cu yd)
How much concrete do you need for an 8×8 slab — diagram

Concrete for an 8×8 slab at different thicknesses

The slab covers 64 square feet. Every extra inch of thickness adds about 0.2 cubic yards. Quantities below include 10% for waste.

ThicknessCubic yards80 lb bags60 lb bags40 lb bags
3.5 in0.76354669
4 in0.87405379
5 in1.09496698
6 in1.35979118
8 in1.7479105157

Bags or ready-mix for this size?

At 0.87 cubic yards, this is a comfortable bag job. A rented drum mixer (or a mixing tub and a hoe for smaller pours) handles it in a few hours.

How heavy is an 8×8 slab?

Normal-weight concrete weighs about 150 lb per cubic foot, so a 4-inch 8×8 slab weighs roughly 3,200 lb (1.6 tons) once cured. Make sure your base is compacted gravel on firm, undisturbed soil.

The math

8 ft × 8 ft × (4 in ÷ 12) = 21.33 cu ft 21.33 cu ft ÷ 27 = 0.79 cu yd +10% waste = 23.47 cu ft 23.47 ÷ 0.6 cu ft per 80 lb bag = 40 bags (rounded up)

Common questions

How many 80 lb bags of concrete for an 8x8 slab?

40 bags for a 4-inch slab including 10% extra (36 with no extra). At 6 inches thick you need 59 bags.

How many yards of concrete for an 8x8 slab 6 inches thick?

1.3 cubic yards including 10% extra, or 1.19 yards exactly.

How many 60 lb bags for an 8x8 slab?

53 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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