Question

how do you convert mm to inches^4

Answer 1

dimensional analysis my friend

1 mm x 1 cm x 1 in
---- -------
10 mm 2.54 cm

now raise everything to 4th power

mm^4 x 1 cm^4 x 1 in^4
---------- ------
10^4 mm^4 (2.54)^4 cm^4