Your elevation or height above sea level is the altitude of your position relative to the average sea level datum. You can get this information online on websites such as Google maps which gives you an approximate value if you key in your location.
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Have you ever wondered 'what is my elevation above sea level'? If you have then you might want to look at a topographical map. This type of map will tell you how close, or far, you are from sea level. You can find more information here: http://www.ghosttowns.com/topotmaps.html