How Much Concrete for a 5x5 Slab? Bags & Yards

Change the numbers

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

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)0.34 cu yd

80 lb bags16

60 lb bags21

40 lb bags31

Exact volume8.33 cu ft (0.31 cu yd)

How much concrete do you need for a 5×5 slab — diagram

Concrete for a 5×5 slab at different thicknesses

The slab covers 25 square feet. Every extra inch of thickness adds about 0.08 cubic yards. Quantities below include 10% for waste.

Thickness	Cubic yards	80 lb bags	60 lb bags	40 lb bags
3.5 in	0.3	14	18	27
4 in	0.34	16	21	31
5 in	0.42	20	26	39
6 in	0.51	23	31	46
8 in	0.68	31	41	62

Bags or ready-mix for this size?

At 0.34 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 5×5 slab?

Normal-weight concrete weighs about 150 lb per cubic foot, so a 4-inch 5×5 slab weighs roughly 1,250 lb (0.6 tons) once cured. Make sure your base is compacted gravel on firm, undisturbed soil.

The math

5 ft × 5 ft × (4 in ÷ 12) = 8.33 cu ft 8.33 cu ft ÷ 27 = 0.309 cu yd +10% waste = 9.17 cu ft 9.17 ÷ 0.6 cu ft per 80 lb bag = 16 bags (rounded up)

Common questions

How many 80 lb bags of concrete for a 5x5 slab?

16 bags for a 4-inch slab including 10% extra (14 with no extra). At 6 inches thick you need 23 bags.

How many yards of concrete for a 5x5 slab 6 inches thick?

0.51 cubic yards including 10% extra, or 0.46 yards exactly.

How many 60 lb bags for a 5x5 slab?

21 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.

How much concrete do you need for a 5×5 slab?