What does SOM quote as capacity for the 16k? Something like 300m/PE6? I think that JB 100lb solid is 0.58mm diameter, and Daiwa quote their SBB as PE6: diameter = 0.44mm
So Length1 = 300, Diameter1 = 0.44mm, Diameter2 = 0.58mm, Length2 = unknown
L1 * (pi * D1^2/4) = L2 * (pi * D2^2/4) <-- full formula?
L1 * D1^2 = L2 * D2^2 <-- cancel out whats the same on each side
L2 = L1 * D1^2 / D2^2 <-- rearrange for unknown
L2 = 300 * 0.44^2 / 0.58^2 <-- add in your numbers
L2 ~ 172m (and maybe a short life for the reel!!!!)
PS: all mathematics were conducted before coffee, I reserve the right to revise results to reduce ridicule.