How Many Bags of Concrete for a 10x10 Slab? (56 x 80lb Bags)

How many bags of concrete for a 10x10 slab? For a standard 4 inch thick 10x10 slab you need 1.23 cubic yards of concrete, which works out to 56 x 80lb bags or 75 x 60lb bags. That is the answer. Everything below shows the math, the other thicknesses, and whether you should be buying bags at all.

How many bags of concrete for a 10x10 slab by thickness?

Thickness changes the number more than anything else. Same 100 square feet, very different bag counts:

• 4 inches thick (33.3 cu ft, 1.23 cu yd): 56 x 80lb bags, 75 x 60lb bags, or 112 x 40lb bags
• 5 inches thick (41.7 cu ft, 1.54 cu yd): 70 x 80lb bags, 93 x 60lb bags, or 139 x 40lb bags
• 6 inches thick (50.0 cu ft, 1.85 cu yd): 84 x 80lb bags, 112 x 60lb bags, or 167 x 40lb bags

Those counts are the bare volume. Add waste before you buy (more on that below). If you want to change the numbers for your own dimensions, run them through the Concrete Calculator instead of doing arithmetic in a parking lot.

How many cubic yards is a 10x10 slab?

A 10x10 slab at 4 inches is 1.23 cubic yards. Here is the math, step by step, so you can reproduce it for any slab.

Step one: convert thickness to feet. 4 inches divided by 12 is 0.333 feet.

Step two: multiply length by width by thickness. 10 x 10 x (4/12) = 33.3 cubic feet.

Step three: convert to cubic yards. There are 27 cubic feet in a cubic yard, so 33.3 / 27 = 1.23 cubic yards.

That is the whole formula. Length x width x depth in feet, then divide by 27. Concrete gets ordered by the cubic yard, so this is the number a ready-mix dispatcher wants to hear.

How do you turn cubic feet into bag count?

Every bag lists a yield on the label. These are the standard yields for mixed concrete:

• 80lb bag = 0.60 cubic feet
• 60lb bag = 0.45 cubic feet
• 40lb bag = 0.30 cubic feet

Divide your volume by the yield. For the 4 inch slab: 33.3 / 0.6 = 56 bags of 80lb mix. Same volume with 60lb bags: 33.3 / 0.45 = 75 bags. With 40lb bags: 33.3 / 0.30 = 112 bags.

Useful anchor: one cubic yard equals 27 cubic feet, which equals 45 x 80lb bags. Memorize that one number and you can sanity check almost any concrete estimate on the spot.

How many 60lb bags for a 10x10 slab?

You need 75 x 60lb bags for a 4 inch 10x10 slab, 93 bags at 5 inches, and 112 bags at 6 inches. The 60lb bags are easier on your back, but you are handling roughly 19 more bags at 4 inches than you would with 80lb mix.

The 40lb bags are worse again: 112 bags at 4 inches. Small bags make sense for post holes and patch jobs. They do not make sense for 100 square feet of slab. If you are set on bagged mix, use 80lb bags and cut the number of trips to the pile.

Should you use bags or order ready-mix?

The practical line sits at roughly 1 cubic yard. Below that, bags are fine. Above it, bagged mix gets punishing fast. A 10x10 slab at 4 inches is 1.23 cubic yards, so it lands just past the line.

Think about what 56 bags actually means. That is 4,480 pounds of dry mix to load, unload, and mix, one bag at a time. A rented mixer might take two 80lb bags per batch, so you are running about 28 batches. And the whole slab has to stay wet and workable while you do it, because a slab poured in pieces over three hours can develop cold joints.

Ready-mix trucks carry about 8 to 10 cubic yards on a full load, so 1.23 yards is a very small order. Most suppliers charge a short-load fee for anything under about 1 cubic yard, and small orders in general cost more per yard than full loads. The tradeoff is that the truck delivers your entire slab in one continuous pour, which is exactly what a slab wants.

Our rule of thumb: under 1 cubic yard, buy bags. Between 1 and 2 yards, it is a real judgment call and depends on how many hands you have. Over 2 yards, call the plant. There is a full breakdown in our guide on bags vs ready-mix.

How much extra concrete should you order for waste?

Add 5 to 10 percent on top of your calculated volume. This is not padding for the sake of it. Real forms are never perfect.

The subgrade dips. The forms bow outward slightly under the weight of wet concrete. Some mix sticks in the wheelbarrow, some spills off the edge of the shovel. A slab that is nominally 4 inches often averages closer to 4.25 inches once poured on real ground.

For our 4 inch 10x10 slab, 10 percent on 56 bags is about 6 extra bags, so buy 62. Unopened bags usually go back to the store. Running three bags short with a half-finished slab is a much worse problem than an extra trip to return them.

Does the gravel base and rebar change the concrete volume?

The gravel base does not change the concrete volume, but it does change where your slab surface sits. A typical slab sits on 4 to 6 inches of compacted gravel. You measure the 4 inch slab thickness from the top of the compacted gravel, not from the bottom of your excavation.

Get this wrong and the error is expensive. If the gravel settles an inch, you are pouring a 5 inch slab without meaning to, and that is 70 bags instead of 56. Compact the base properly and screed it flat before you order anything.

Rebar and welded wire mesh displace a trivial amount of volume. Ignore them in your estimate. Do not ignore them in the slab itself: a 10x10 slab carrying anything heavier than a patio table generally wants mesh or a #3 rebar grid, held up in the middle of the pour depth rather than lying on the dirt. Whether you need 4, 5, or 6 inches depends on the load, and that is covered in how thick should a concrete slab be.

How many bags for other slab sizes near 10x10?

Slab plans move around. If your 10x10 becomes a 10x12, the bag count changes a lot. At 4 inches thick:

• 8x10 slab: 26.7 cu ft, 45 x 80lb bags
• 10x10 slab: 33.3 cu ft, 56 x 80lb bags
• 10x12 slab: 40.0 cu ft, 67 x 80lb bags
• 12x12 slab: 48.0 cu ft, 80 x 80lb bags

Notice the 8x10. At 45 bags it is exactly 1 cubic yard, right on the bags-versus-truck line. Shaving two feet off one side of a 10x10 removes 11 bags of mixing. That is worth knowing before you set the forms.

For any size not on this list, including odd shapes, thickened edges, and footings, the Concrete Calculator handles it in a few seconds. For the wider picture on estimating slabs, footings, columns, and steps, start with our pillar guide on how much concrete do I need.

Bottom line

A 4 inch thick 10x10 slab needs 1.23 cubic yards of concrete, which is 56 x 80lb bags, 75 x 60lb bags, or 112 x 40lb bags. Add 5 to 10 percent for waste and buy about 62 x 80lb bags. Go to 5 inches and it jumps to 70 bags; go to 6 inches and it is 84. At this size you are right on the edge where a ready-mix truck starts making more sense than a mixer and a long afternoon. Check your own numbers with the Concrete Calculator before you buy anything.