Record ID Prefix | Object Type from Record ID Prefix | Prefix of an Object in Salesforce.

We know there are two types of record-id are present in salesforce (18 digit -- Case Insensitive,15 digit -- Case Sensitive). Only 3 digit of ids represent object type .The following is a list of the Salesforce Standard Object ID prefixes

Object	Prefix
Account	001
NOTE	002
Contact	003
User	005
Opportunity	006
Activity	007

 Please check below post for more detail

https://help.salesforce.com/apex/HTViewSolution?id=000005995&language=en_US

If you want to get the Prefix of any object . Please try below code.

String keyPrefix = Account.sObjectType.getDescribe().getKeyPrefix();
System.debug('PREFIX--' + keyPrefix );

If you want to get the Object Name from RecordId then please try below code.

public class SchemaGlobalDescribeToGetObjectName
{
    public static String findObjectNameFromRecordIdPrefix(String recordIdOrPrefix)
 {
  String objectName = '';
        try
  {
            String IdPrefix = String.valueOf(recordIdOrPrefix).substring(0,3); 
            Map<String, Schema.SObjectType> gd =  Schema.getGlobalDescribe(); 
            for(Schema.SObjectType stype : gd.values())
   {
                Schema.DescribeSObjectResult r = stype.getDescribe();
                String prefix = r.getKeyPrefix();
                if(prefix!=null && prefix.equals(IdPrefix))
    {
                    objectName = r.getName();
                    System.debug('Object Name! ' + objectName);
                    break;
                }
            }
        }catch(Exception e){
            System.debug(e);
        }
        return objectName;
    }
}

If you want to Get the Object prefix by Workbench then please try below step :-

The easiest way to find out which key prefix maps to which object is by using a tool like the workbench . After you log into workbench, go to and pick an object from the pick list.

Step 1 :- Login in to Workbench

URL :- https://workbench.developerforce.com/

Step 2:- Info > Standard & Custom Objects 

Step 3:- Then select your object

Thanks

Amit Chaudhary