sqlserver varchar turn numbers range queries

SELECT COUNT
	( [size] ) num 
FROM
	crawler_publish_property 
WHERE
	CAST ( ISNULL( [size], 0 ) AS NUMERIC ( 10, 2 ) ) >= 0 
	AND CAST ( ISNULL( [size], 0 ) AS NUMERIC ( 10, 2 ) ) < 50

Numeric (10,2) represents a total of 10 bits, 2 bits decimal number, that is the maximum integer bits of this field is 8 bits