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Cubic yards and 60/80 lb bags of concrete for a slab, plus the gravel base underneath.
With these inputs:
| Result | Value |
|---|---|
| Concrete | 1.6 yd³ |
| 80 lb bags | 72 bags |
| Gravel base | 2.67 tons |
| Ready-mix vs bags | $436 – $636 vs $396 – $540 |
| Slab area | 120 sq ft |
| Thickness | 4 in |
| Concrete (incl. 8% over-pour) | 1.6 yd³ (43.2 cu ft) |
| 80 lb bags at 0.6 cu ft each | 72 bags |
| Gravel base (crusher run, +20%) | 1.78 yd³ · 2.67 tons |
| Base cost | $59 – $107 |
More than about 60 bags is a lot of mixing — above 1 cubic yard, ready-mix is usually cheaper and gives a stronger, more consistent slab. Most plants charge a short-load fee under 4 to 5 yards.
Every concrete slab needs a compacted gravel base, so this calculator does both: it returns the concrete in cubic yards and in 60 lb or 80 lb bags, the crushed-stone base in tons, and a cost comparison between bagged mix and ready-mix delivery.
About 45 bags. Each 80 lb bag yields 0.6 cubic feet and a cubic yard is 27 cubic feet. With 60 lb bags it takes 60, and with 40 lb bags it takes 90.
A 10 by 10 foot slab 4 inches thick is 1.23 cubic yards before waste, or about 1.33 yards with an 8% allowance. That is 60 bags of 80 lb mix — at that size, a ready-mix delivery is usually easier and similar in cost.
Four inches of compacted crusher run under patios and sidewalks, and six inches under driveways or on clay. For a 10 by 12 foot slab, a 4 inch base is about 1.8 tons of gravel including compaction.
Bags are cheaper below about one cubic yard. Above that, ready-mix at $160 to $210 per yard usually wins, even with a short-load fee, and it saves hours of mixing.
Four inches for patios, walkways, and shed floors; five to six inches for driveways and garage floors; and thicker, with reinforcement, for heavy equipment.
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