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Concrete Slab: How Many Bags of Concrete Mix Do I Need?

Make sure you have enough concrete for your project. These calculations help you estimate how many bags of concrete mix you need for a concrete slab or pad.

Smoothing Concrete with a Trowel

Calculating the Concrete Mix You Need

The tables below give you estimates for the number of 50- or 60-lb bags you need for concrete slabs of various sizes. Remember:

  • Before beginning any excavation, call 811 to check for underground utilities.
  • Moving and maneuvering bags of concrete mix takes significant effort. Enlist a helper.
  • Follow package instructions and cautions when working with concrete mix.
  • The calculations are estimates only. Your project needs may vary.

Estimating 50-lb Bags of Concrete Mix

4-inch Depth   6-inch Depth
     
Square
Feet

Number of
Bags Needed

  Square
Feet
Number of
Bags Needed
5 5   5 7
10 9   10 14
15 14   15 20
20 18   20 27
25 22   25 33
30 27   30 40
35 31   35 47
40 36   40 53
45 40   45 60
50 44   50 66
55 49   55 73
60 53   60 79
65 58   65 86
70 62   70 93
75 66   75 99
80 71   80 106
85 75   85 112
90 79   90 119
95 84   95 125
100 88   100 132

Estimating 60-lb Bags of Concrete Mix

4-inch Depth   6-inch Depth
     
Square 
Feet

Number of 
Bags Needed

  Square 
Feet
Number of 
Bags Needed
5 4   5 6
10 8   10 12
15 12   15 17
20 15   20 23
25 19   25 28
30 23   30 34
35 26   35 39
40 30   40 45
45 34   45 50
50 38   50 56
55 41   55 62
60 45   60 67
65 49   65 73
70 52   70 78
75 56   75 84
80 60   80 89
85 63   85 95
90 67   90 100
95 71   95 106
100 75   100 112

Estimating 80-lb Bags of Concrete Mix

4-inch Depth   6-inch Depth
     
Square 
Feet

Number of 
Bags Needed

  Square 
Feet
Number of 
Bags Needed
5 3   5 5
10 6   10 9
15 9   15 13
20 12   20 17
25 14   25 21
30 17   30 25
35 20   35 30
40 23   40 34
45 25   45 38
50 28   50 42
55 31   55 46
60 34   60 50
65 37   65 55
70 39   70 59
75 42   75 63
80 45   80 67
85 48   85 71
90 50   90 75
95 53   95 80
100 56   100 84

Estimating 90-lb Bags of Concrete Mix

4-inch Depth   6-inch Depth
     
Square 
Feet

Number of 
Bags Needed

  Square 
Feet
Number of 
Bags Needed
5 3   5 4
10 6   10 8
15 8   15 12
20 11   20 16
25 13   25 19
30 16   30 23
35 18   35 27
40 21   40 31
45 23   45 35
50 26   50 38
55 28   55 42
60 31   60 46
65 33   65 50
70 36   70 54
75 38   75 57
80 41   80 61
85 43   85 65
90 46   90 69
95 48   95 72
100 51   100 76