Ice that is less than 4″ thick is an invitation for disaster. Many people say that five days of sub-zero temps is long enough to freeze a pond or lake enough to walk on it. This is actually not too inaccurate.

If you’re curious about the science behind how this is determined check out this link: http://www.sciencebits.com/StandingOnIce

There’s even a formula for this from Science Bits no, really:

[latex]{\delta E } = \epsilon \rho \delta x + \int_0^{z=x}\left| {d T(z,x) \over dx} \right| c \rho \delta x dz = \epsilon \rho \delta x + \Delta T \left.{z^2 \over 2 x^2}\right|_{z=0}^{z=x} c \rho \delta x = \left( \epsilon \rho + {c \rho \Delta T \over 2} \right) \delta x .[/latex]

What does this even mean!?

As time progresses, the thickness increases x→x+δx. This implies two things. First, freezing of a layer δx wide takes place. Second, the whole x wide layer cools. Both require energy. Per unit area of ice, it is:

Who has time to figure this out!? Five days of freezing temps and we’re good right!?

If for example the average temperature is 2 degrees below freezing, then it would require about 4 days to freeze 10 cm of ice, which is about the minimum necessary to safely travel on foot (and do some ice fishing, if it’s your cup of tea).

Okay that sounds familiar — I think we’re good to go!

Ultimately, be certain to check with the local warden for ice thickness.