A 10 × 10 ft slab is one of the most common DIY pours: a shed base, a hot tub pad, a small patio or the floor of a garden room. The short answer is that a standard 4-inch-thick 10×10 slab needs about 56 bags of 80 lb concrete mix, or 59 bags once you add 5% for spillage. That is 1.23 cubic yards of concrete before waste, or 1.30 cubic yards with it.
Below is how that number is worked out, what changes if you use 60 lb or 40 lb bags or pour a thicker slab, and when it makes more sense to stop mixing bags and order ready-mix instead. If you just want your own number, the concrete calculator does the maths for any size and thickness.
Quick answer: bags for a 10×10 slab
These figures assume a flat, square 10 × 10 ft slab (100 sq ft) and the typical yield printed on US bags of pre-mixed concrete. The figures in brackets include 5% extra, which is what we recommend you buy.
| Slab thickness | Concrete needed | 80 lb bags (0.60 cu ft each) | 60 lb bags (0.45 cu ft each) | 40 lb bags (0.30 cu ft each) |
|---|---|---|---|---|
| 4 in | 33.3 cu ft / 1.23 cu yd | 56 (59 with 5% extra) | 75 (78 with 5% extra) | 112 (117 with 5% extra) |
| 5 in | 41.7 cu ft / 1.54 cu yd | 70 (73 with 5% extra) | 93 (98 with 5% extra) | 139 (146 with 5% extra) |
| 6 in | 50.0 cu ft / 1.85 cu yd | 84 (88 with 5% extra) | 112 (117 with 5% extra) | 167 (175 with 5% extra) |
Bag yields vary slightly between brands, so check the back of the bag before you buy. Most US 80 lb bags make about 0.60 cubic feet of concrete, which is where these numbers come from.
How to work it out yourself
Every concrete estimate comes down to one idea: work out the volume of the slab, then divide it by how much concrete one bag makes.
- Convert the thickness to feet. 4 inches is 4 ÷ 12 = 0.333 ft.
- Multiply length × width × thickness. 10 × 10 × 0.333 = 33.3 cubic feet.
- Add a margin for waste. 33.3 × 1.05 = 35.0 cubic feet. Ground is never perfectly flat, forms bow slightly and some concrete always ends up on the tools and in the wheelbarrow.
- Divide by the bag yield. 35.0 ÷ 0.60 = 58.3 bags of 80 lb mix.
- Always round up. You cannot buy a third of a bag, and running short halfway through a pour is far worse than having one bag left over. Buy 59.
To turn cubic feet into cubic yards, the unit ready-mix suppliers use, divide by 27. So 33.3 cu ft ÷ 27 = 1.23 cubic yards.
How thick should a 10×10 slab be?
Thickness makes a bigger difference to the bag count than most people expect. Going from 4 to 6 inches adds 50% more concrete.
- 4 inches is the usual thickness for a shed base, garden path, small patio or a pad for an AC unit.
- 5 inches suits a hot tub pad or a slab that will carry heavy garden equipment.
- 6 inches is the norm for a slab that a car or small vehicle will drive on.
If your slab will carry a structure such as a garage or garden room, or you are unsure, check your local building code before you pour. Many areas have rules on thickness, reinforcement and footings for anything you will build on.
Bags or ready-mix: which is cheaper?
At typical US prices in September 2026, an 80 lb bag of concrete mix costs around $7, so 59 bags come to roughly $413. The same 1.30 cubic yards of ready-mix at around $175 a yard is about $227, before any delivery charges.
That gap is not the whole story. Many ready-mix plants add a short-load fee for small orders, which can wipe out much of the saving on a slab this size. Ask your local supplier for a delivered price on 1.5 cubic yards and compare it with the bag total.
The bigger difference is labour. Fifty-nine 80 lb bags is about 4,700 lb of material to lift, mix and place, and each bag needs mixing with water. With a hand-mixed wheelbarrow that is a long, hard day for two people, and the first section can start to set before the last is poured. As a rough rule:
- Under about 1 cubic yard, bags are usually the practical choice.
- Between 1 and 2 cubic yards (where a 10×10 slab sits), rent a small electric mixer and line up at least two helpers, or get a ready-mix quote.
- Over 2 cubic yards, ready-mix is almost always easier and more consistent.
Don’t forget the base
A slab is only as good as what is underneath it. For most garden slabs, lay 4 inches of compacted gravel (crushed stone or road base) before you pour. For a 10×10 slab, that is about 1.23 cubic yards of gravel before compaction; order 10–15% more, because it settles as you tamp it down. The gravel calculator will give you the tonnage for your supplier.
For slabs that will carry weight, add wire mesh or rebar set on small supports so it sits in the middle of the slab rather than on the ground. It will not stop concrete cracking altogether, but it holds the pieces together so cracks stay tight.
If you buy concrete in metric bags
In Canada, concrete mix is often sold in 30 kg bags. A 10 × 10 ft slab at 4 inches is about 0.94 m³, or 0.99 m³ with 5% extra. Many 30 kg bags make roughly 0.014 m³, which works out at about 71 bags, but yields differ between brands, so read the bag and adjust. Switch the concrete calculator to Canada and metric to see it in cubic metres.
Common mistakes that leave you short
- Measuring the thickness at one corner. Dig-outs are rarely level. Measure the depth in several places and use the average, or the deepest point if the ground slopes.
- Forgetting the edges. If you are thickening the edges of the slab (common for sheds), add that extra volume.
- Using nominal board sizes. A “2×4” used as a form is only 3.5 inches tall, so a slab formed with 2x4s is 3.5 in thick, not 4.
- Rounding down. Always buy the next whole bag. Unopened bags can usually be returned if you keep the receipt.
Frequently asked questions
How many 80 lb bags of concrete make a cubic yard?
About 45 bags, because a cubic yard is 27 cubic feet and each 80 lb bag makes about 0.60 cubic feet. With 60 lb bags you need 60, and with 40 lb bags you need 90.
How many bags of concrete for a 10×10 slab 6 inches thick?
About 84 bags of 80 lb mix, or 88 once you add 5% for waste. At this size, ready-mix is usually the better option.
Can I pour a 10×10 slab in sections?
You can, using a board to divide the slab and pouring one half at a time, but each joint is a weak point. For a slab this small, it is better to get enough help and mixing capacity to pour it all in one go.
How long before I can walk or build on it?
You can usually walk on it after 24 to 48 hours. Concrete typically reaches about 70% of its strength after 7 days and its full design strength after 28. Keep it damp for the first few days, especially in hot weather, so it does not dry out too fast and crack.
Work out your own slab: try the free concrete calculator for bags and ready-mix costs, or the paver calculator if you are weighing up pavers instead of a solid slab.
Figures are estimates for planning. Bag yields, prices and local building rules vary, so check them with your supplier before you buy.
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