> line-height: calc(1em + 0.5rem);

Even cleaner imho, at least in theory, if you dont use 'em' but 'ex' for the relative sizing, the x-height of the element's first available font.

Good looking leading is often more influenced by the x-height of a typeface than by cap height (try setting Verdana and Times with the same line-height). So especially if your design has more than one typeface, using ex makes it more consistent.

Caveat: If the metrics are not set correctly in the font file, FF on Mac, and the Windows browsers will freak out. Should not be a problem with system fonts, but if you use web fonts, keep an eye on that.

I usually also set a unitless fallback, at least on the html element.