This spreadsheet lets you convert practically any unit of measure to another in the same category... Convert feet to meters, yards to inches, kilometers to miles, liters to gallons, US Dollars to British Pound Sterling, ounces to grams, tons to pounds or pounds to stone... you get the idea. You can try all sorts of categories of measurement, including distance (miles, feet, meters, km, mm), weight (pounds, grams, stone, kg, mg, ounces), volume (ounces, liters, kl, ml, etc.) , currency (USD, GBP, CAD, ESP, etc) , temperature (f, c, kelvin) - and probably more...

This spreadsheet uses the power of Google's search box feature for conversions - where you can type something as simple as "100 feet in meters" and it will convert for you.

Here's a preview of the spreadsheet: