Number of Drops per Header Size

- FYI #332
FYI #332

This Piping Header & Drop Size Tool is to be used as a guideline only.

The tool calculates the available area of the piping header and determines the equivalent area of the selected drop size that equals the header area.

In addition to this tool we generally recommend that the fluid velocity in the pipe be between 5-7 feet per second and/or the resultant pressure drop be below 2.3 pounds per square inch per 100 foot of pipe.

Consult factory for additional assistance. See FYI-166 “Water Distribution & Pipe Sizing”.

    • For a header size of 1/4″
      Drop Size
      Number of Drops
      1/8″
      2.1
      1/4″
      1
    • For a header size of 3/8″
      Drop Size
      Number of Drops
      1/8″
      4.5
      1/4″
      2.1
      3/8″
      1
    • For a header size of 1/2″
      Drop Size
      Number of Drops
      1/8″
      8
      1/4″
      3.8
      3/8″
      1.8
      1/2″
      1
    • For a header size of 3/4″
      Drop Size
      Number of Drops
      1/8″
      16
      1/4″
      8
      3/8″
      3.6
      1/2″
      2
      3/4″
      2
    • For a header size of 1″
      Drop Size
      Number of Drops
      1/8″
      30
      1/4″
      14
      3/8″
      6.6
      1/2″
      3.7
      3/4″
      1.8
      1″
      1
    • For a header size of 1-1/4″
      Drop Size
      Number of Drops
      1/8″
      60
      1/4″
      28
      3/8″
      13
      1/2″
      7
      3/4″
      3.8
      1″
      2
      1-1/4″
      1
    • For a header size of 1-1/2″
      Drop Size
      Number of Drops
      1/8″
      88
      1/4″
      41
      3/8″
      19
      1/2″
      11
      3/4″
      5.3
      1″
      2.9
      1-1/4″
      1.5
      1-1/2″
      1
    • For a header size of 2″
      Drop Size
      Number of Drops
      1/8″
      164
      1/4″
      77
      3/8″
      36
      1/2″
      20
      3/4″
      10
      1″
      5.5
      1-1/4″
      2.7
      1-1/2″
      1.9
      2″
      1
    • For a header size of 2-1/2″
      Drop Size
      Number of Drops
      1/8″
      255
      1/4″
      120
      3/8″
      56
      1/2″
      31
      3/4″
      16
      1″
      8
      1-1/4″
      4.3
      1-1/2″
      2.9
      2″
      1.6
      2-1/2″
      1
    • For a header size of 3″
      Drop Size
      Number of Drops
      1/8″
      439
      1/4″
      206
      3/8″
      97
      1/2″
      54
      3/4″
      27
      1″
      15
      1-1/4″
      7.4
      1-1/2″
      5
      2″
      2.7
      2-1/2″
      1.7
      3″
      1
    • For a header size of 3-1/2″
      Drop Size
      Number of Drops
      1/8″
      632
      1/4″
      297
      3/8″
      139
      1/2″
      78
      3/4″
      38
      1″
      21
      1-1/4″
      11
      1-1/2″
      7
      2″
      3.9
      2-1/2″
      2.5
      3″
      1.4
      3-1/2″
      1
    • For a header size of 4″
      Drop Size
      Number of Drops
      1/8″
      867
      1/4″
      407
      3/8″
      191
      1/2″
      107
      3/4″
      53
      1″
      29
      1-1/4″
      15
      1-1/2″
      10
      2″
      5.3
      2-1/2″
      3.4
      3″
      2
      3-1/2″
      1.4
      4″
      1
    • For a header size of 4-1/2″
      Drop Size
      Number of Drops
      1/8″
      1148
      1/4″
      539
      3/8″
      253
      1/2″
      141
      3/4″
      70
      1″
      38
      1-1/4″
      19
      1-1/2″
      13
      2″
      7
      2-1/2″
      4.5
      3″
      2.6
      3-1/2″
      1.8
      4″
      1.3
      4-1/2″
      1
    • For a header size of 5″
      Drop Size
      Number of Drops
      1/8″
      1525
      1/4″
      715
      3/8″
      335
      1/2″
      188
      3/4″
      93
      1″
      51
      1-1/4″
      26
      1-1/2″
      17
      2″
      9
      2-1/2″
      6
      3″
      3.5
      3-1/2″
      2.4
      4″
      1.8
      4-1/2″
      1.3
      5″
      1
    • For a header size of 6″
      Drop Size
      Number of Drops
      1/8″
      2414
      1/4″
      1133
      3/8″
      531
      1/2″
      297
      3/4″
      147
      1″
      80
      1-1/4″
      40
      1-1/2″
      28
      2″
      15
      2-1/2″
      9
      3″
      5.5
      3-1/2″
      3.8
      4″
      2.8
      4-1/2″
      2.1
      5″
      1.6
      6″
      1
    • For a header size of 7″
      Drop Size
      Number of Drops
      1/8″
      3433
      1/4″
      1635
      3/8″
      766
      1/2″
      425
      3/4″
      212
      1″
      118
      1-1/4″
      58
      1-1/2″
      40
      2″
      21
      2-1/2″
      14
      3″
      8
      3-1/2″
      5.5
      4″
      4
      4-1/2″
      3
      5″
      2.3
      6″
      1.4
      7″
      1
    • For a header size of 8″
      Drop Size
      Number of Drops
      1/8″
      4795
      1/4″
      2251
      3/8″
      1954
      1/2″
      590
      3/4″
      292
      1″
      160
      1-1/4″
      80
      1-1/2″
      55
      2″
      20
      2-1/2″
      19
      3″
      10
      3-1/2″
      7.6
      4″
      5.5
      4-1/2″
      4.2
      5″
      3
      6″
      2
      7″
      1.3
      8″
      1
    • For a header size of 9″
      Drop Size
      Number of Drops
      1/8″
      6369
      1/4″
      2990
      3/8″
      1401
      1/2″
      783
      3/4″
      388
      1″
      212
      1-1/4″
      107
      1-1/2″
      73
      2″
      39
      2-1/2″
      25
      3″
      14
      3-1/2″
      10
      4″
      7.3
      4-1/2″
      5.5
      5″
      4.2
      6″
      2.6
      7″
      1.8
      8″
      1.3
      9″
      1
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