>65 - 71 cm
||Smith et al., Body size evolution across the Geozoic, Annual Review of Earth and Planetary Sciences, Vol. 44 :523-553, 2016 DOI: 10.1146/annurev-earth-060115-012147 link p.534 2nd paragraph
||Shear WA, Kukalová-Peck J. 1990. The ecology of Paleozoic terrestrial arthropods: the fossil evidence. Can. J. Zool. 68: 1807–34 doi 10.1139/z90-262
||P.534 2nd paragraph: "Other clades too evolved fantastically large size over Earth history. Perhaps the most famous are the giant dragonflies and griffinflies of the middle to late Paleozoic. These taxa evolved during the Permo-Carboniferous, amid a marked increase in atmospheric oxygen partial pressure (Berner et al. 2007). Meganeura and other genera of similarly sized flying insects were about three times the size of the largest flying insects today, with wingspans exceeding 65–71 cm (primary source). Their evolution has been tied to the absence of other aerial predators (Bechly 2004) coupled with the much higher oxygen content/density of the atmosphere at this time, which may have facilitated breathing and flight (Graham et al. 1995, Chapelle & Peck 1999, Harrison et al. 2006, Clapham & Karr 2012). Recent laboratory studies confirm that increasing atmospheric oxygen partial pressure can lead to the evolution of significantly larger insect body mass in less than a dozen generations (Harrison et al. 2006, Kaiser et al. 2007)."