If you are visiting a snow covered area or town and you want to get an idea of how much snow is on the ground, make sure you don't measure the drift snow. Drift snow is usually snow that has blown against an object and settled there for example snow settled against trees, rocks or roadside gutters or even in gardens. Sure its fun to measure snow in these places but it wont give you a clear representation of the average amount of settled snow in the area. Look for a place that is fairly open (not football ovals, roads or paddocks exposed to wind and melt) that is free from trees and other obstacles and make a few measurements in different spots with your fingers, if you don't have a ruler. I know the exact measurement from the tip of my index finger to the first crease, which comes in handy in these situations :) As a rough guide in Australia, one centimetre of snow usually equates to 1mm of rain, ie: a moderate fall of say, 5cm of snow, is equal to around 5mm of rain falling. Remember, the snow in most places outside of the Australian Alps melts very quickly, so even the above method wont really indicate how much snow has actually fallen, just how much is left on the ground.
The method I now use is to place a piece of plywood in a level place in my yard which is protected from strong winds (strong winds can blow snow away) and not likely to be in an eddy situation (where winds swirl around, re-depositing the same snow). Also, try to keep the board away from depressions in the ground where snow can accumulate to exaggerated depths. During a snowfall, regularly wipe the board clear, measuring the snow that has accumulated, in centimetres. If you don't measure the snow regularly, say every hour or so in heavier falls, the snow will tend to pack down and melt, (especially Blue Mountains snow) which will then affect the accuracy of your measurements. Also, if you watch the snow as it falls onto the board, you will get an idea of what might be drift snow and what is actual falling snow. Thanks to Laurier Williams from Australian Weather News - for recommending the plywood method to me.