Levels can be determined by weighing your collection not on a scale, but a single uncracked ostrich egg*. If the egg still remains standing after you let go of your collection, your level is definitely under 10.
If the egg shatters, the next step is to lay out each and every single car on your bed. Do not overlap or stack anything, even packaged items. If your collection does not cover the mattress entirely, your level is between 11 and 30, depending on how much surface area is covered.
If you covered your entirely mattress and you still have cars left over, take those remaining cars, tally it up. Take that number, multiply by 0.4, add 67, then multiply by 4.4, and round up to the next whole number. That is how you determine your level.
*You can substitute an ostrich egg with 6 chicken eggs or 4 duck eggs.
Please note this isn't actually true.