I have a simple webform that will allow unauthenticated users to input their information, including name. I gave the name field a limit of 50 characters to coincide with my
In the UK, there are a few government standards which deal successfully with the bulk of the UK population -- the Passport Office, the Driver & Vehicle Licensing Agency, the Deed Poll office, and the NHS. They use different standards, obviously.
Changing your name by Deed Poll allows 300 characters;
There is no legal limit on the length of your name, but we impose a limit of 300 characters (including spaces) for your full name.
The NHS uses 70 characters for patient names
PATIENT NAME
Format/length: max an70
The Passport Office allows 30+30 first/last and Driving Licenses (DVLA) is 30 total.
Note that other organisations will have their own restrictions about what they will show on the documents they produce — for HM Passport Office the limit is 30 characters each for your forename and your surname, and for the DVLA the limit is 30 characters in total for your full name.