0.8-0.9mm according to the service manual.
kawasaki zl600
This is a real problem for lots of motorcyclists. We must first establish two criteria. 1. How low do you need. 2.What style of motorcycle do you like/dislike. The lowest modern Japanese Race Replica bike I am aware of is Honda's CBR400RR (The Baby Blade). This still requires an inside leg of approx. 30". It is the little sister to the famous CBR900RR Fireblade. The most popular all rounder which comes in a variety of styles is the SUZUKI SV650. Although these are not that low standard, they can easily (and cheaply) be lowered. The standard seat height is 805mm (31.7"). The rear suspension can be lowered 25-30mm using a kit. The front yolks can then be lowered 5-10mm & you can purchase cut away seats quite cheaply. The overall effect lowers the machine quite a bit but does not effect the handling too much. If cruisers are your style then these fall into two catergories, V-Twins or in-line 4 cylinder bikes. The latter were quite popular in the 80's & 90's but seem to have gone out of production. A very low one was the Kawasaki ZL600 Eliminator. This had a seat height of approx. 26-27" & could be lowered a little bit more. These can still be bought in good condition from dealerships & from the internet. The V-twins have since taken over with lots of American & Japanese variations. One of the lowest reasonably priced Harley Davidsons would be the XLH 883 Sportster but of course you may want a larger engine capacity & Harley do low versions of most of their machines and a key factor is the position of the foot controls. With Harley their machines although quite heavy offer standard mid pegs or longer legged forward controls. The Japanese do various cruiser style bikes although the best for weight / height comdination would seem to be the Yamaha Dragstar (V-Star in the US), this comes in various engine sizes 650cc-1100cc. They also did an earlier version called the Virago, very popular with shorter folk. Kawasaki do few twin that are quite low the VN, VZ, VZS, ETC. Of course you may already have explored these avenues & have found none low enough which means probably an exspensive custom build depending on your requirements. Or alternatively a second hand custom bike.