Enter an address at walkscore.com, and the site calculates a "walk score" between 1 and 100 based on information from Google Maps. Try it, it's pretty cool!
Walkscore.com calculates how many different types of destinations are theoretically within walking distance, and then generates the score. You can see it tallying up results as it lists some of those destinations.
The site freely admits "a number of factors that contribute to walkability are not part of our algorithm," including street design/width, public transit options, safety (both crime and accident levels) and streetscape aesthetics ("Are there walking paths? Are buildings close to the sidewalk with parking in back? If buildings have large parking lots in front, they are less inviting to pedestrians.").
Considering how many important factors aren't in the algorithm, it does a pretty good job!
My neighborhood gets a mid-range score, which seems reasonable. My parents' neighborhood, which has many more destinations in easy walking distance, gets a higher score. My sister's neighborhood, which I consider walker-hostile beyond the immediate few blocks, does poorly, as does my in-laws' area, which I find frustrating when trying to walk anywhere. My aunt's compact New York neighborhood, which always felt walkable when I visited as a kid, scores highly. The New York area where my husband's grandparents used to live, which is exceptionally walkable, racks up 92 out of 100.
Try an address or two and see for yourself.