We don't often get candidates of her caliber.

Could anyone tell me what that might mean?

Thanks

We don't often get candidates of her caliber.

Caliber (or calibre as we'd spell it here in the UK) has two meanings. Firstly it's the word for the inside diameter of a tube, most often used with firearms or artillery and by association with ammunition - so a .45 Magnum, a 9mm Walther PPK, a .22 bullet, a 5 inch howitzer and so on. Caliber also means "quality" or "degree of worth" - usually with a tacit implication of good. Thus, your sentence means "We don't often get candidates as good as she is."