How deep is the frost line where you live?

Enter a ZIP code for an estimate built from NOAA weather-station freezing data, adjusted for your soil type.

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Range shows estimated frost depth in typical soil from the mildest to the coldest county.

How it works

Freezing index. NOAA measured how cold and how long winters get at 3,110 weather stations. We use the 100-year value: a winter colder than about 99 out of 100.
Your location. We blend the three stations nearest your ZIP code, weighted by distance.
Frost depth. The modified Stefan equation turns the freezing index into inches of frost for sand, loam and clay.

Full methodology →

Why it matters

Water expands about 9% when it freezes. Soil above the frost line swells and lifts anything shallow: deck piers, fence posts, slab edges and water lines. Setting footings below the frost line keeps them still.

Common questions

What is the frost line?

The frost line is the deepest point that soil freezes in winter. Footings above it can heave as the ground freezes and thaws, which cracks foundations, lifts deck posts and pops fence posts out of the ground.

How deep should I dig footings?

Below your local frost line and at least 12 inches below undisturbed soil. Your building department sets the exact depth; use our estimate to plan and budget.

Is this the same as my building code?

No. Codes set a fixed frost depth for each jurisdiction, often rounded up for safety. Our numbers estimate how deep frost actually gets, plus the range codes commonly use in similar climates.