User blog comment:Xilinoc/Ch. 605 - Don't Call My Name/@comment-7805464-20141113164640/@comment-26420452-20141113170302

In Japan, the ri's value has changed over time and during the last era it was used, it equaled 3.9 km. But 3900 km would be insanely too much, unless Ichibei was planning to bury Yhwach somewhere near the earth's center.

So I guess the ri in question is about 500 m, and yes, 1000 ri = 500 km.