I just recently purchased a Rose Hair Tarantula, but I don't know if it is male or female...how do I tell?

Females are always larger in size when compared to males. Is it's legs extraordinarily skinny when you compare it to other ones? If it is, it's male. Trust me, I have a Chilean rose-hair. Also, their life expectancy. If it only lives 10 years, it's male. If it lives 15-30, it's female.