Here's a simple way to use Google's unit conversion feature, while typing shorter queries. Instead of searching Google for [6 lbs to kg], you can use [6 lbs =]. Just add the equal sign to the value you want to convert and Google will use the right measurement unit most of the time.
Here's another example: [68 f =]. The query is shorter than [68 f to c] or [6 fahrenheit to celsius]. Unfortunately, [20 c =] doesn't convert temperature, since c is the speed of light, so you'll have to use [20 c to f].
You can use Google's dropdown to pick other measurement units or you can edit the value and the result will change as yo type.
This trick also works in Chrome's omnibox, Firefox's search box, Safari's address bar: