To be honest- I am afraid I have gone so far with my plan in imperial- that I don’t think I can go back now. As for the lumber- I am hoping I can get planks exactly 3/4 inches- and if I have to get it custom cut- cost be damned- this is going to be a bespoke beehive. I will make the plan open source once I am done- hopefully the imperial measurements will make it more universally applicable? I think I am am the right path as far as langstroth compatibility goes- here is a list of dimensions of standard langstroth boxes in Australia from a supplier:
Sizes. For supers, the sizes are :
Full Depth - A depth of 9 1/2 inches (241.3 mm)
Manley - 6 5/8 inches (168.3 mm)
WSP - 7 1/2 inches (190.5 mm)
Ideal - 5 3/4 inches (146.1 mm)
Half Depth - 4 7/8 inches ( 124 mm )
The frame depth is usually 5/16 - 3/8 inch (7.9 - 9.5 mm) less than the depth of the super.
the mm dimensions are just too messy to work with- whilst the imperial measurements are nice rounded figures?