How Much Concrete for a 10x10 Slab?

Updated 2026-07-19

The 10×10 slab is the most common DIY concrete project in America — shed pads, hot tub bases, AC pads, generator pads, and a thousand backyard landing spots. It is also the perfect size to learn concrete math on, because the numbers are clean and a small mistake will not bankrupt you.

Here is exactly how much concrete a 10×10 takes at both common thicknesses, what that means in bags, and the honest answer on whether you should mix it yourself.

The math: 100 square feet times thickness

A 10×10 slab is 100 square feet. At the standard 4-inch thickness, multiply by 0.333 feet (4 divided by 12) to get 33.3 cubic feet. Divide by 27 to convert to cubic yards: 1.23 yards. That is the number everything else hangs on.

Measure inside the forms, not the stakes and string. If your forms wander 2 inches off each way — a 10.2 × 10.2 slab — you have just added 4% to your volume before a single drop is poured.

Bag counts for a 10×10 slab

Bag yields are printed on the back of every bag — an 80 lb bag of standard mix makes 0.60 cubic feet, a 60 lb bag makes 0.45. Do not assume the heavier bag is the better deal; run the price per cubic foot both ways at the store.

1. 4 inches thick, 80 lb bags (0.60 cu ft yield): 33.3 ÷ 0.60 = 56 bags.
2. 4 inches thick, 60 lb bags (0.45 cu ft yield): 33.3 ÷ 0.45 = 74 bags.
3. 6 inches thick (hot tubs, heavy sheds): 50 cu ft — 84 bags of 80 lb.
4. Add 10% for waste and an uneven subgrade: 61 bags of 80 lb for the 4-inch slab, 92 for the 6-inch.

Should you really hand-mix 56 bags?

Be honest about the labor. Fifty-six 80 lb bags is 4,480 pounds you will move twice — once into the cart, once into the mixer. With a rented mixer and one helper, expect the better part of a day of mixing, and you will be finishing the first half of the slab while the last batches are still spinning.

At 1.23 yards you are right at the break-even point for ready-mix. Many plants will deliver a single yard, with short-load fees that vary widely by market. Get a quote before committing: 56 bags at $5 to $7 each is $280 to $390 plus the mixer rental, and a delivered yard often lands in the same ballpark with a fraction of the work. Past 1.5 yards, the truck wins every time.

Four inches or six?

Four inches over 4 inches of compacted gravel handles sheds, patio furniture, grills, and foot traffic — that covers most 10×10 pads. Go to 6 inches for a hot tub (a filled six-person tub tops 5,000 lb), a workshop with heavy machinery, or anywhere a vehicle tire might clip an edge.

If a structure will sit on the slab — say, a shed with framed walls — thicken the perimeter to 8 inches deep and about 8 inches wide. That turned-down edge is what actually carries the building, and it only adds a few bags to the total.

The base matters as much as the bags

The number-one cause of cracked DIY slabs is not bad concrete — it is bad dirt. Strip the topsoil, compact 4 inches of crushed gravel, and pour on that. A slab poured over soft topsoil or mulch will settle and crack no matter how many bags you bought.

Lay 6-mil poly under the slab if it will sit inside an enclosed space, and set wire mesh or rebar on chairs in the middle third of the slab — not on the ground, where it does nothing.

Before you buy a single bag, plug your exact dimensions and thickness into the concrete calculator to confirm the bag count and yardage — adjusting a number on a screen beats adjusting it on the driveway.