Dinky army toys are mostly 1:60 scale, that is 60 inches is represented by one inch on the model. But the scale is not constant across the whole "army". Dinky had an idea of toys that fit in the pocket, so smaller toys were made slightly larger and larger models were made smaller and consequently cheaper and easier to handle. Another theory is that the casting machines they used initially had a maximum size, that was until the introduction of "Supertoys".

Here is my take on the scale of each model. I based this on the easiest dimension to measure to a toy which is the wheelbase.