Ice Depth Calculator
Estimate lake ice thickness from your local weather station's daily temperature and wind — and see what that ice is likely safe for. Free, no sign-up.
What it does
Pulls Weather Data
Load the last two weeks of daily readings from any Weather Underground personal weather station, or upload a CSV, paste data, or enter days by hand.
Estimates Thickness
Applies Stefan's formula to accumulated freezing degree days, net of thaw days and adjusted for wind.
Calibrates to You
Tune the ice growth coefficient for snow cover, or enter an auger measurement as a baseline and project forward from there.
Charts & Export
Track ice depth and temperature over time with interactive charts, and export the full calculation to CSV.
How it works
Ice grows roughly with the square root of how much cold it has been exposed to. The calculator tracks that cold as freezing degree days: each day, the number of degrees the average temperature sat below 32°F. Warm days count against the total as thawing degree days.
FDD = max(0, 32°F − daily avg temp) TDD = max(0, daily avg temp − 32°F) Net AFDD = ΣFDD − ΣTDD Wind factor = max(0.7, 1 − avg wind mph / 50) Ice depth (in) = α × √Net AFDD × Wind factor
The growth coefficient α defaults to 1.0 for clear lake ice; snow-covered ice grows more slowly, around 0.5–0.8. Wind keeps water moving under forming ice, so sustained wind trims the estimate by up to 30%. If you've drilled a hole and measured, enter that as a baseline and the calculator only accumulates from that date forward.
Ice thickness guide
General guidance for clear, solid ice. White or slushy ice is roughly half as strong.
| Ice depth | Rating |
|---|---|
| Under 2 in | Unsafe — stay off |
| 2–4 in | Caution — walking only |
| 4–5 in | Ice fishing on foot |
| 5–8 in | Snowmobile / ATV |
| 8–12 in | Car / light truck |
| 12+ in | Heavy vehicle |
Estimates only. Ice thickness varies across a body of water, and this model doesn't account for snow load, currents, springs, inlets, or pressure ridges. Always check ice thickness on site before going out.
Check your lake
Grab a nearby weather station URL and get an estimate in seconds.