On a single PNR one SWU is good for wherever you are flying as long as 12 hours break does not occur on It'l legs, and sometimes it is down to 4 hours "stop" sudden death if da.bomb tacks on a restrictive US ticket to an It'l one - I had that occur earlier this month.

We are using one SWU each soon for Anchorage-DEN-BOS-LAX-SYD, which must be around 15,000 miles.