How much concrete do you need for a 4×4 slab?

A 4×4 ft slab poured 4 inches thick needs 0.2 cubic yards (5.3 cu ft) of concrete. With 10% extra for waste, buy 10 bags of 80 lb premix or order 0.22 yards of ready-mix.

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The calculator below is pre-filled for this project. Adjust any value — including feet and inches — and the results update instantly.

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Tip: enter feet and inches in separate boxes, or use decimals (10 ft 6 in = 10.5 ft).

Your results

Concrete to buy (incl. 10% extra)0.22 cu yd
80 lb bags10
60 lb bags14
40 lb bags20
Exact volume5.33 cu ft (0.2 cu yd)
How much concrete do you need for a 4×4 slab — diagram

Concrete for a 4×4 slab at different thicknesses

The slab covers 16 square feet. Every extra inch of thickness adds about 0.05 cubic yards. Quantities below include 10% for waste.

ThicknessCubic yards80 lb bags60 lb bags40 lb bags
3.5 in0.1991218
4 in0.22101420
5 in0.27131725
6 in0.33152030
8 in0.43202740

Bags or ready-mix for this size?

At 0.22 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 a 4×4 slab?

Normal-weight concrete weighs about 150 lb per cubic foot, so a 4-inch 4×4 slab weighs roughly 800 lb (0.4 tons) once cured. Make sure your base is compacted gravel on firm, undisturbed soil.

The math

4 ft × 4 ft × (4 in ÷ 12) = 5.33 cu ft 5.33 cu ft ÷ 27 = 0.198 cu yd +10% waste = 5.87 cu ft 5.87 ÷ 0.6 cu ft per 80 lb bag = 10 bags (rounded up)

Common questions

How many 80 lb bags of concrete for a 4x4 slab?

10 bags for a 4-inch slab including 10% extra (9 with no extra). At 6 inches thick you need 15 bags.

How many yards of concrete for a 4x4 slab 6 inches thick?

0.33 cubic yards including 10% extra, or 0.3 yards exactly.

How many 60 lb bags for a 4x4 slab?

14 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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