There are various methods you can use to control SQL error logs files.
While there is never a one size fits all solution in for anything in SQL, After googling around most of the solutions I am finding are listing 5MB or 10MB in their solutions. Example How to manage the SQL Server error log @ microsoft.com You can have 5 error logs at 1GB each or 99 error logs at 5MB each, and have about the same history.
I don't find anyone making actual "recommendations" on SQL error log size.
I imagine the place to start is at a percentage of your RAM, but I really don't know.
SQL Error Log, how do I determine the most appropriate error log size?