A SQL float is a double according to the documentation for SQLDbType.
A float in SQL is a Double in the CLR (C#/VB). There's a table of SQL data types with the CLR equivalents on MSDN.
And normally you would never want to use float in SQL Server (or real) if you plan to perform math calculations on the data as it is an inexact datatype and it will introduce calculation errors. Use a decimal datatype instead if you need precision.