Using people for measurements, and assuming 1.75 height, HQ-19 missile canisters seem to be around 0.65 m wide and 5.85 m long (that's without the gas cylinder part of the container at the bottom)
That's of course likely subject to 10% error margin, due to imprecise measurements.
The missile inside should be somewhat smaller, but probably not that much. Another 5-10% margin?
Anyway, upward of 500mm missile diameter and 5 m missile length seems plausible.
That'd make it a bit shorter than THAAD missile (little over 6 m) but also quite a bit wider (370mm at its widest)
If anyone has the exact truck tire model and dimensions, or truck model and dimensions, that would help make the measurement a bit more precise.