c.1300, impose a tax on, from Old French taxer impose a tax (13c.), from Latin taxare evaluate, estimate, assess, handle, also censure, charge, probably a frequentative form of tangere to touch (see tangent). Sense of burden, put a strain on first recorded 1670s; that of censure, reprove is from 1560s.
The average depth of frost penetration ranges from 25 inches (64 cm) in southwestern South Dakota to 50 inches (127 cm) in. the northeast. Depth of frost depends on the amount of residue cover, soil moisture content, and the amount and timing of. snowfalls in relation to temperature extremes.
Thickness is 16 inches min. As far as for down to dig and set your footer that will depend on local code and the frost line depth in one area is different in another here in Kentucky it's 18inches so the answer would be 16inches wide and set 18inches deep with a thickness of 6 inches.