min

The 'min' validation rule is the direct opposite of the 'max' rule. It can be used to ensure that a field value is greater than or equal to the provided parameter. If the field is a string, the parameter will refer to the length of the string in characters. For numerical values, the comparison will be made mathematically. For file upload fields the comparison will be made upon the size of the file in bytes.

size

The 'size' rule can be used to ensure that the value of the field is of a given size provided by the rule parameter. If the field is a string, the parameter will refer to the length of the string in characters. For numerical values, the comparison will be made mathematically. For file upload fields the comparison will be made upon the size of the file in bytes.

you can try the size. i hope it works....