Scale is the size of the kit against the real suit: at 1/144 every meter becomes about 7 mm. HG, RG and EG are 1/144, MG and RE/100 are 1/100, and PG is 1/60, per Bandai's grade page. Bandai's page for the HGUC Xi Gundam says the suit is over 26 meters, so even at 1/144 it comes out at about 18 cm.
26 m divided by 144 is 18.1 cm; the same suit at 1/100 would be 26 cm and at 1/60 about 43 cm (our arithmetic).
Read Oct 14, 2026. The definition is ours; facts come from the pages above.