How many bags of concrete do I need for a 5×8 slab?

At 4 inches thick, a 5×8 slab takes 25 bags of 80 lb concrete mix, 33 bags of 60 lb mix or 49 bags of 40 lb mix, including 10% extra.

How many yards of concrete for a 5×8 slab?

0.49 cubic yards at 4 inches thick, 0.62 at 5 inches and 0.74 at 6 inches, before adding extra for waste.

How much does a 5×8 concrete slab cost?

The concrete alone for a 4 inch 5×8 slab costs about $163 in 25 bags of 80 lb mix (at about $7 a bag) or about $124 for 0.75 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $240 to $480 for 40 sq ft.

How much does a 5×8 slab weigh?

About 1 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).

Concrete for a 5×8 slab

0.49 cubic yards (25 × 80 lb bags)

for a 5×8 ft slab 4 inches thick: 13.3 cu ft. Bag counts include 10% extra; at 6 inches you need 0.74 yards.

A 5×8 foot slab covers 40 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 13.3 cubic feet of concrete, or 0.49 cubic yards. That is a small enough pour for bagged mix: 25 bags of 80 lb at about $163.

Concrete for a 5×8 slab by thickness

Thickness	Cubic yards	Cubic feet	80 lb bags	60 lb bags	40 lb bags
3 in	0.37	10	19	25	37
4 in	0.49	13.3	25	33	49
5 in	0.62	16.7	31	41	62
6 in	0.74	20	37	49	74
8 in	0.99	26.7	49	66	98

Bag counts include 10% extra for spillage and uneven ground. Cubic yards and cubic feet are the exact volume.

How it’s worked out

Convert the thickness to feet: 4 in ÷ 12 = 0.333 ft.
Multiply length × width × thickness: 8 × 5 × 0.333 = 13.33 cu ft.
Divide by 27 for cubic yards: 13.33 ÷ 27 = 0.494 cu yd.
Add 10% and divide by the bag yield: 14.67 ÷ 0.6 = 25 bags of 80 lb mix (rounded up).

Under the slab, plan on 4 inches of compacted gravel: about 0.49 cubic yards. For driveways and anything that carries a vehicle, go to 5 or 6 inches and add rebar or wire mesh.

Change the numbers

Length (ft) Width (ft) Thickness (in) Extra for waste (%) Price per 80 lb bag ($) Ready-mix price per yard ($)

Concrete needed

0.49 cubic yards

13.3 cubic feet. With 10% extra, order 0.54 yards or 25 bags of 80 lb mix.

Area	40 sq ft
Volume	13.3 cu ft (0.49 cu yd)
80 lb bags	25 (about $163)
60 lb bags	33
40 lb bags	49
Ready-mix to order	0.75 yd (about $124 before delivery fees)
Weight of the slab	1 tons

Other slab sizes

Questions

How many bags of concrete do I need for a 5×8 slab?: At 4 inches thick, a 5×8 slab takes 25 bags of 80 lb concrete mix, 33 bags of 60 lb mix or 49 bags of 40 lb mix, including 10% extra.
How many yards of concrete for a 5×8 slab?: 0.49 cubic yards at 4 inches thick, 0.62 at 5 inches and 0.74 at 6 inches, before adding extra for waste.
How much does a 5×8 concrete slab cost?: The concrete alone for a 4 inch 5×8 slab costs about $163 in 25 bags of 80 lb mix (at about $7 a bag) or about $124 for 0.75 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $240 to $480 for 40 sq ft.
How much does a 5×8 slab weigh?: About 1 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).