numeric data in varchar datatype

I have a column with varchar data type but has numeric data in itI know I can't use arithmetic operation for varcharThis is my queryselect * from table1where col1> 500.00Msg 8115, Level 16, State 8, Line 38Arithmetic overflow error converting varchar to data type numeric.obviously it gives me this error.what functions should I use to convert the data type?I appreciate your helpThanks