Thanks everyone for the suggestions.
I am a complete beginner at Python (I’ve been learning for about 3 days) and this is my first programming language, so everything’s new to me.
All the same I think I’ve written something that calculates the dimensions in realtime. If people who are more experienced at Python can take a look over it and let me know if it makes sense and is appropriately optimised I would be very grateful.
cont = GameLogic.getCurrentController()
owner = cont.owner
#Get Number of Vertexes
VertexQty = owner.meshes.getVertexArrayLength(0)
#Define Vertexe Number Variable
VertexNumber = 0
#Define Blank Lists to hold XYZ coordinates
vxlist = 
vylist = 
vzlist = 
#Go through each vertex and establish coordinates. Append XYZ values to self respective lists.
for i in range(0, VertexQty):
vx, vy, vz = owner.meshes.getVertex( 0, i).getXYZ()
#Establish the biggest and smallest values
smallestx = min(vxlist)
biggestx = max(vxlist)
smallesty = min(vylist)
biggesty = max(vylist)
smallestz = min(vzlist)
biggestz = max(vzlist)
xdimension = biggestx + smallestx*-1
ydimension = biggesty + smallesty*-1
zdimension = biggestz + smallestz*-1
print "X Dimension ="
print "Y Dimension ="
print "Z Dimension ="
Thanks again for everyone’s input