Excel – How to sort a list of numbers, by its last 3 digits in Excel

You can make a table to split the values:

For each column, use the headings (row 1) and formulas (row 2+):

A1: text    A2: (your section numbers)
B1: dot1    B2: =FIND(".",A2,1)  
C1: dot2    C2: =IFERROR(FIND(".",A2,B2+1),LEN(A2)+1)  
D1: num1    D2: =VALUE(MID(A2,1,B2-1))  
E1: num2    E2: =IFERROR(VALUE(MID(A2,B2+1,C2-B2-1)),0)  
F1: num3    F2: =IFERROR(VALUE(MID(A2,C2+1,LEN(A2)-C2)),0)  

This appears as:

      A      B      C      D      E      F

1   text   dot1   dot2   num1   num2   num3
2   1.1       2      4      1      1      0
3   1.1.3     2      4      1      1      3
4   2.10.7    2      5      2     10      7

Then you can do a custom sort by columns num1, num2 and num3.

It sounds as if your numbers are being interpreted as text by Excel. A good indication of this is that they automatically align to the left of each cell. Numbers normally are aligned to the right.

If this is the case, a simple fix is to move into a cell, press F2 then Enter. Repeat for each cell containing the numbers that don't sort. This works by putting the cell into edit mode and then out again. If the contents can be interpreted as a number then Excel converts it to a number.

If you have too many cells to do this manually, you can use the VALUE function to create another column contain true numeric values and then paste them (by value) back over the offending cells.