The Spotlight search on your Mac allows you to find and preview files on your system, and can be quite convenient for opening applications, or in later versions of OS X, looking up quick bits of information. Spotlight also interfaces with the OS X calculator so you can use it to run quick calculations, but in addition, you can use it to perform a number of supported conversions, including currency, area, length, speed, and mass.
To do this, you do not need any special syntax for your search. Just press Command-Space (or whatever hotkey you use to activate Spotlight), and then enter the number along with a reference to what that value represents. For instance, you can enter “12.345 Dollars” or “$12.345” to see this amount in different currencies.
Similarly, you can enter labels or symbols to specify other common metrics, and then have Spotlight show relevant conversions. For instance, entering “12.345 millimeters” (or just using “mm”) will allow for length conversions from millimeters to another length you specify. For some area conversions, you can use “^2” or “^3” to specify squared and cubed units such as “feet⁻^3” for cubic feet.

When conversions are run, they will show up with the calculator chosen. You can then copy the result directly from Spotlight, or press Enter to open the calculator.
As with all calculations done in Spotlight, these will highlight the Calculator app when computed. Pressing Enter will open the calculator, but you can also directly copy the result by pressing Command-C, and then pasting it in an application of your choosing.
Hey, that’s pretty cool but it doesn’t work on my MBP 10.9.5. Simple math works with the Calculator showing but the dollar conversion and mm conversion doesn’t work.
William,
I think the unstated assumption we all have to make from now on is that “OS X” on macissues.com really means “at least OS X 10.10”.
@ J Boytone, thanks for the clarification. Since the article says ‘in later versions of OS X’ I thought it might work. I will assume 10.10 in all instances in the future.
Also: google has had this feature for a long time.