32"
no Frost
The frost line in the city of Chicago is thought to be 36 inches. The average Chicago winter does not exceed the 36 inch frost line, but extremely cold winters can.
In western Pennsylvania the frost line falls at 36", when installing underground waterlines 42" is perfered.
no Frost
24"
frost line in pa is 42 inches
The frost line in Salt lake city is 30 in. I would assume that that is average for most of the state.
24in
one metre
42 inches
42"
3ft