Not as common as miles or laps, but it still pops up a few times a year. Cup has done 500km at Phoenix since the first Cup race there, and both Busch and ARCA did 500km at Talladega before shortening the race distance in recent years. Trucks have always used 350/400km for their races at Texas and did the same for Vegas until just a coupe years ago

Far more common on the road courses. All three Cup road course races are measured in km, same for Xfinity at the Roval and the Trucks up at Mosport