Create sequential numbers in a field in ArcMap using Python in the Field Calculator

Summary

Instructions provided describe how to create sequential numbers in a field in ArcMap using Python in the Field Calculator.

Note:
ArcMap is in Mature support and will be retired March 1, 2026. There are no plans for future releases of ArcMap, and it is recommended that you migrate to ArcGIS Pro. See Migrate from ArcMap to ArcGIS Pro for more information.

Procedure

Note:
The code in this article generates sequential numbers for unsorted data based on the OID or FID order. If the data is sorted on a field, the generated numbers are not sequential.

1. Create a new short integer field. Refer to ArcMap: Adding fields for instructions.
2. Right-click the new field and select Field Calculator.
3. Set the Parser to Python.
4. Check the check box for Show Codeblock.
5. Paste the following into the Pre-Logic Script Code:

rec=0 
def autoIncrement(): 
 global rec 
 pStart = 1  
 pInterval = 1 
 if (rec == 0):  
  rec = pStart  
 else:  
  rec += pInterval  
 return rec

6. Paste the following code in the smaller box below the Pre-Logic Script Code:

autoIncrement()

7. Click OK. The following image is an example of a field with sequential numbers populated using the Python code: