How much concrete do you need for a 10×20 slab?

A 10×20 ft slab poured 4 inches thick needs 2.47 cubic yards (66.7 cu ft) of concrete. With 10% extra for waste, buy 123 bags of 80 lb premix or order 2.72 yards of ready-mix.

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Your results

Concrete to buy (incl. 10% extra)2.72 cu yd
80 lb bags123
60 lb bags163
40 lb bags245
Exact volume66.67 cu ft (2.47 cu yd)
How much concrete do you need for a 10×20 slab — diagram

Concrete for a 10×20 slab at different thicknesses

The slab covers 200 square feet. Every extra inch of thickness adds about 0.62 cubic yards. Quantities below include 10% for waste.

ThicknessCubic yards80 lb bags60 lb bags40 lb bags
3.5 in2.38107143214
4 in2.72123163245
5 in3.4153204306
6 in4.07184245367
8 in5.43245326489

Bags or ready-mix for this size?

At 2.72 cubic yards you are in the gray zone between bags and a truck. 123 bags of 80 lb weigh about 9,840 lb in total — get a ready-mix quote (ask about short-load fees) and compare it with the bag price before deciding.

How heavy is a 10×20 slab?

Normal-weight concrete weighs about 150 lb per cubic foot, so a 4-inch 10×20 slab weighs roughly 10,000 lb (5 tons) once cured. Make sure your base is compacted gravel on firm, undisturbed soil.

The math

10 ft × 20 ft × (4 in ÷ 12) = 66.67 cu ft 66.67 cu ft ÷ 27 = 2.469 cu yd +10% waste = 73.33 cu ft 73.33 ÷ 0.6 cu ft per 80 lb bag = 123 bags (rounded up)

Common questions

How many 80 lb bags of concrete for a 10x20 slab?

123 bags for a 4-inch slab including 10% extra (112 with no extra). At 6 inches thick you need 184 bags.

How many yards of concrete for a 10x20 slab 6 inches thick?

4.07 cubic yards including 10% extra, or 3.7 yards exactly.

How many 60 lb bags for a 10x20 slab?

163 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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