Concrete Slab Calculator (with Gravel Base)
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.
What you'll need
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IMAYCC Cement Mixer, 2100W Electric Concrete Mixer with 6 Speed, 110V Handheld Mud Mixer for Motar,Paint, Grout, Plaster, Thinset,Fodder Stirring Tool
$51.90
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DURASACK Heavy Duty Sandbags with Ties, 14x26, Empty, Green, Pack of 10
$9.89
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TICONN 4.80/4.00-8 Tire, 14.5" Flat Free Wheelbarrow Tire and Wheel
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NoCry Clear Safety Glasses for Men and Women with Anti-Fog and Scratch Resistant Wrap Around Lenses, Adjustable Temples and Nose Pads — ANSI Z87 Certified Protective Eyewear with 100% UV Shielding
$13.99
View on Amazon →Prices as of Sep 25, 2026, 6:18 PM UTC. Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.
Get the Gravel & Stone Calculator app for Android
Estimate gravel, stone, sand, and mulch on the job site, save projects, and share quantities with your supplier.
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Frequently asked questions
- How many 80 lb bags of concrete are in a yard?
- 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.
- How much concrete do I need for a 10x10 slab?
- 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.
- How much gravel do I need under a concrete slab?
- 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.
- Is it cheaper to mix concrete or order ready-mix?
- 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.
- How thick should a concrete slab be?
- 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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