Yeah, so this is a calculated size for Fairy Tail's Planet. It is obviously a massive lowball since we are only shown this small shot of the planet and we can't use curvature scaling.
Magnolia to Hargeon = 370 Km = 49.25 px
370 Km/49.25 px = 7.51269 Km per px
Fiore = 588.32 px = 4419.86578 Km = 4419865.78 Meters
Fiore = 4419865.78 Meters = 35 px
4419865.78 Meters/35 px = 126281.88 Meters per px
Earthland Circumference = 677.76 px = 85588806.98 Meters
Earthland Diameter = 27243763 Meters
Earthland Radius = 13621882 Meters
Earth Circumference = 40075000 Meters
Mass of Earth = 5.972e+24 Kg
Earthland Mass = (Earthland's Size/Earth's Size)^3*Earth's Mass
(85588806.98/40075000)^3*5.972e+24 = 5.817684e+25 Kg (Class Z)
U = (3*Gravitational Constant*(Mass of object in Kg^2))/(5*Radius in Meters)
GBE = (3*6.67408x10^-11*(5.817684e+25^2))/(5*13621882) = 2.3 Yottatons (Planet level+)