# How many Bags of Concrete do I need for a Slab

Written By Sourabh Negi

I cover structural design, construction technology and building materials.

## How many Bags of Concrete do I need for a Slab?

One of the main questions before laying concrete is how many bags of concrete do I need for a Slab or any concrete component? Right estimation is important, to avoid excess and deficiency.

To determine the number of bags of concrete, you should know the dimensions of the concrete slab (i.e. Length, width and thickness. Once you know the measurements you can calculate the volume of the concrete slab. Premix Concrete bags generally available in the USA are 40lb, 60lb, 80lb and 90lb. A 40lb yields about 0.30 cubic feet.

A 60 lb cement bag yields about 0.45 cubic feet. An 80 lb concrete bag cover about 0.60 cubic feet. A 90 lb concrete bag covers about 0.68 cubic feet.

Dividing the volume with yield will give you the number of bags required for that slab.

## How many bags of concrete do I need for a 2×2 Slab

1. Let us assume the thickness of the slab is 4 inches.
2. The square footage of the slab will be 2×2 = 4 square feet.
3. Now calculate the volume of the slab,  Square footage x (thickness in feet).

=4x(4/12)= 4 x 0.3333= 1.332 cubic feet.

1. Let us assume we are using a 40 lb concrete bag. 1 bag of 40 lb yields 0.30 cubic feet.
2. No. of bags for 2×2 slab 4 inches thick = 1.332/0.30= 4.44
3. We can also add 10% extra for wastage. 4.44 + 4.44×10%= 4.88 bags. Thus you will need 5 bags of 40lb weight for a 2×2 slab, 4 inches thick.

## How many bags of concrete do I need for a 2×4 Slab

1. Let us assume the thickness of the slab is 6 inches. Convert it to feet. 6 inch = 6/12= 0.5 foot.
2. Calculate the Square footage of the slab i.e. 2 x 4 = 8 square feet.
3. Calculate the volume of the slab = 8 x 0.5 = 4.0 cubic feet.
4. Let us assume we are using a 60 lb bag, the yield of 1 60 lb bag = 0.45 cubic feet.
5. No. of bags for 2×4 slab 6 inches thick = 4.0/0.45 =8.88
6. Add 10% extra for wastage, = 8.88×10%+8.88=9.77. Thus for a 2 x 4 slab, 6-inch thick 10 bags of 60lb weight will be required.

## How many bags of concrete do I need for a 4×4 slab

1. Assume a thickness of 4 inches.
2. The square footage of the slab will be 4×4 = 16 square feet.
3. The volume of the slab = 16 x 0.3333 = 5.33 cubic feet.
4. Suppose we are using an 80 lb bag, the yield of 80 lb bag = 0.60 cubic feet.
5. No. of bags of concrete for 4×4 slab 4 inches thick = 5.33/0.60 = 8.88
6. Add 10% extra for wastage, = 8.88×10%+8.88=9.77= 10 bags

## How many bags of concrete do I need for a 4×6 slab

1. Let the thickness of the slab be 6 inches.
2. Area of slab = 4×6= 24 square feet.
3. Volume of the slab = 24x(6/12) = 12 cubic feet.
4. For a 60 lb concrete bag, the number of bags = 12/0.45= 26,67 bags
5. Add 10% extra for wastage, = 26.67×10%=26.67= 29.34= say 29 bags.

## How many bags of concrete do I need for a 4×8 slab

1. Let the thickness of the slab be 4 inches.
2. Area of slab = 4×8= 32 square feet.
3. Volume of the slab = 32x(4/12) = 10.67 cubic feet.
4. For a 40 lb concrete bag, the number of bags = 10.67/0.30= 35.57 bags
5. Add 10% extra for wastage, = 35.57×10%+35.57= 39.13= say 39 bags.

How many bags of Concrete do I need for a Slab?

We have made a table wherein the first column size of the slab is mentioned. Square footage for that size of slab is calculated in 2nd column. No. of 40lb, 60lb, and 80 lb bags are calculated for a 4-inch thick slab and a 6-inch thick slab.

## FAQs

### How many bags of concrete do I need for a 2×2 Slab

The square footage for the 2×2 slab is 4.
No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 5
60 lb bags: 3
80 lb bags: 2
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 7
60 lb bags: 5
80 lbs bags: 4

### How many bags of concrete do I need for a 2×4 Slab

The square footage for the 2×4 slab is 8.
No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 10
60 lb bags: 7
80 lb bags: 5
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 15
60 lb bags: 10
80 lbs bags: 7

### How many bags of concrete do I need for a 3×3 Slab

The square footage for the 3×3 slab is 9.
No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 11
60 lb bags: 7
80 lb bags: 6
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 17
60 lb bags: 17
80 lbs bags: 8

### How many bags of concrete do I need for a 4×3 Slab

The square footage for the 4×3 slab is 12.
No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 15
60 lb bags: 10
80 lb bags: 7
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 22
60 lb bags: 15
80 lbs bags: 11

### How many bags of concrete do I need for a 4×4 slab

The square footage for the 4×4 slab is 16.
No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 20
60 lb bags: 13
80 lb bags: 10
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 29
60 lb bags: 20
80 lbs bags: 15

### How many bags of concrete do I need for a 4×5 slab

The square footage for the 4×5 slab is 20.
No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 24
60 lb bags: 16
80 lb bags: 12
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 37
60 lb bags: 24
80 lbs bags: 18

### How many bags of concrete do I need for a 4×6 slab

The square footage for the 4×6 slab is 24.
No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 29
60 lb bags: 20
80 lb bags: 15
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 44
60 lb bags: 29
80 lbs bags: 22

### How many bags of concrete do I need for a 4×8 slab

No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 39
60 lb bags: 26
80 lb bags: 20
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 59
60 lb bags: 39
80 lbs bags: 29

### How many bags of concrete do I need for a 4×12 slab

No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 59
60 lb bags: 39
80 lb bags: 29
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 88
60 lb bags: 59
80 lbs bags: 44

### How many bags of concrete do I need for a 5×5 slab

No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 31
60 lb bags: 20
80 lb bags: 15
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 46
60 lb bags: 31
80 lbs bags: 23

### How many bags of concrete do I need for a 5×10 slab

No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 61
60 lb bags: 41
80 lb bags: 31
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 92
60 lb bags: 61
80 lbs bags: 46

### How many bags of concrete do I need for a 6×4 slab

No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 29
60 lb bags: 20
80 lb bags: 15
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 44
60 lb bags: 29
80 lbs bags: 22

### How many bags of concrete do I need for a 6×6 slab

No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 44
60 lb bags: 29
80 lb bags: 22
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 66
60 lb bags: 44
80 lbs bags: 33

### How many bags of concrete do I need for a 7×7 slab

No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 60
60 lb bags: 40
80 lb bags: 30
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 90
60 lb bags: 60
80 lbs bags: 45

### How many bags of concrete do I need for 8×8 slab

No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 78
60 lb bags: 52
80 lb bags: 39
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 117
60 lb bags: 78
80 lbs bags: 59

### How many bags of concrete do I need for a 8×10 slab

No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 98
60 lb bags: 65
80 lb bags: 49
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 147
60 lb bags: 98
80 lbs bags: 73

### How many bags of concrete do I need for a 9×9 slab

No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 99
60 lb bags: 66
80 lb bags: 50
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 149
60 lb bags: 99
80 lbs bags: 74

### How many bags of concrete do I need for a 10×8 slab

No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 98
60 lb bags: 65
80 lb bags: 49
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 147
60 lb bags: 98
80 lbs bags: 73

### How many bags of concrete do I need for a 10×10 slab

No. of bags of Concrete for a 2-inch thick slab
40 lb bags: 61
60 lb bags: 41
80 lb bags: 31
No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 122
60 lb bags: 81
80 lb bags: 61
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 183
60 lb bags: 122
80 lbs bags: 92

### How many bags of concrete do I need for a 10×12 slab

No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 147
60 lb bags: 98
80 lb bags: 73
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 220
60 lb bags: 147
80 lbs bags: 110

### How many bags of concrete do I need for a 10×15 slab

No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 183
60 lb bags: 122
80 lb bags: 92
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 275
60 lb bags: 183
80 lbs bags: 138

### How many bags of concrete do I need for a 10×20 slab

No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 244
60 lb bags: 163
80 lb bags: 122
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 367
60 lb bags: 244
80 lbs bags: 183

### How many bags of concrete do I need for a 12×8 slab

No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 117
60 lb bags: 78
80 lb bags: 59
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 176
60 lb bags: 117
80 lbs bags: 88

### How many bags of concrete do I need for a 12×10 slab

No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 147
60 lb bags: 98
80 lb bags: 73
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 220
60 lb bags: 147
80 lbs bags: 110

### How many bags of concrete do I need for a 12×12 slab

No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 176
60 lb bags: 117
80 lb bags: 88
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 264
60 lb bags: 176
80 lbs bags: 132

### How many bags of concrete do I need for a 12×16 slab

No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 235
60 lb bags: 156
80 lb bags: 114
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 352
60 lb bags: 235
80 lbs bags: 176

### How many bags of concrete do I need for a 12×20 slab

No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 293
60 lb bags: 196
80 lb bags: 147
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 440
60 lb bags: 293
80 lbs bags: 220

### How many bags of concrete do I need for a 12×24 slab

No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 352
60 lb bags: 235
80 lb bags: 176
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 528
60 lb bags: 352
80 lbs bags: 264

### How many bags of concrete do I need for a 15×15 slab

No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 275
60 lb bags: 183
80 lb bags: 138
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 413
60 lb bags: 275
80 lbs bags: 206

### How many bags of concrete do I need for a 16×16 slab

No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 313
60 lb bags: 209
80 lb bags: 156
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 469
60 lb bags: 313
80 lbs bags: 235

### How many bags of concrete do I need for a 20×20 slab

No. of bags of Concrete for a 4-inch thick slab
40 lb bags: 489
60 lb bags: 326
80 lb bags: 244
No. of bags of Concrete for 6 inch-thick slab
40lb bags: 733
60 lb bags: 489
80 lbs bags: 367