How many Inches....of snow ?

As other people have said, the rule-of-thumb is that 1" rain = 10" snow, but the reality is that it can vary tremendously around that. Here is a quote from the National Snow and Ice Data Center website:

"The water content of snow is more variable than most people realize. While many snows that fall at temperatures close to 32oF and snows accompanied by strong winds do contain approximately one inch of water per ten inches of snowfall, the ratio is not generally accurate. Ten inches of fresh snow can contain as little as 0.10 inches of water up to 4 inches depending on crystal structure, wind speed, temperature, and other factors. The majority of U.S. snows fall with a water-to-snow ratio of between 0.04 and 0.10."

http://www.nsidc.org/snow/faq.html

The rule of thumb is 10" of snow is equivalent to 1" of rain.

10 inches