About FrostDepthCheck
Why this exists
People look up the frost line when they are about to dig: deck footings, fence posts, a shed, a water line across the yard. What they mostly find is a colour-band map with no source, or a single state figure that ignores the difference between a valley and a mountain county. FrostDepthCheck works the number out for each of 3,144 counties from that county's nearest NOAA weather station, shows the arithmetic, and says who has the final word.
Where the numbers come from
Temperatures are NOAA's 1991-2020 climate normals, daily mean and spread, from the station nearest each county. Those become a freezing index (how cold, for how long), and the Modified Berggren equation turns that into a depth for one stated soil under snow. The steps and their weak points are in how the estimate is made.
What this site will not tell you
It will not tell you the frost line depth your building department enforces. That value is adopted locally in IRC Table R301.2(1), and no national list of the adopted values exists. Every county page says so, and this guide explains why the two numbers differ.
Who runs this
FrostDepthCheck is an independently run site. It is not affiliated with NOAA, the International Code Council, any building department, or any contractor or supplier.
Written by
County pages and guides are generated by AI software from the cited NOAA data and published references. No engineer or editor reviews a page before it publishes. The temperatures come from NOAA, not from AI; the depth comes from a published equation applied the same way to every county.