How many Bags of Concrete do I need for a Slab

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Written By Sourabh Negi

I cover structural design, construction technology and building materials.

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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.

Concrete BagYield in cubic feetYield in a cubic yard (divided by 27)
20 lb0.15 cubic feet0.005
40 lb0.30 cubic feet0.011
60 lb0.45 cubic feet0.017
80 lb0.60 cubic feet0.022
90 lb0.68 cubic feet0.025
The yield of Concrete bags in Cubic Feet and Cubic Yard

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.

How many bags of concrete do I need for aSquare footageVol. of the 4-inch thick SlabVol of the 6 inch thick slabNo. of bags of 40 lb Concrete No. of bags of 40 lb Concrete No. of bags of 60 lb Concrete No. of bags of 60 lb Concrete No. of bags of 80 lb Concrete No. of bags of 80 lb Concrete
4 inch thick slab6 inch thick slab4 inch thick slab6 inch thick slab4 inch thick slab6 inch thick slab
2×2 Slab41.332.00573524
2×4 slab82.674.00101571057
3×3 Slab93.004.50111771168
4×3 Slab124.006.0015221015711
4×4 slab165.338.00202913201015
4×5 Slab206.6710.00243716241218
4×6 slab248.0012.00294420291522
4×8 slab3210.6716.00395926392029
4×12 Slab4816.0024.00598839592944
5×5 Slab258.3312.50314620311523
5×10 Slab5016.6725.00619241613146
6×4 Slab248.0012.00294420291522
6×6 Slab3612.0018.00446629442233
7×7 Slab4916.3324.50609040603045
8×8 slab6421.3332.007811752783959
8×10 Slab8026.6740.009814765984973
9×9 Slab8127.0040.509914966995074
10×8 Slab8026.6740.009814765984973
10×10 slab10033.3350.00122183811226192
10×12 slab12040.0060.001472209814773110
10×15 Slab15050.0075.0018327512218392138
10×20 slab20066.67100.00244367163244122183
12×8 Slab9632.0048.00117176781175988
12×10 Slab12040.0060.001472209814773110
12×12 slab14448.0072.0017626411717688132
12×16 Slab19264.0096.00235352156235117176
12×20 Slab24080.00120.00293440196293147220
12×24 slab28896.00144.00352528235352176264
15×15 Slab22575.00112.50275413183275138206
16×16 slab25685.33128.00313469209313156235
20×20 Slab400133.33200.00489733326489244367
No. of bags of Concrete in a 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

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