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by Bob

One of the most useful tools I've found for Makers is Google's built-in calculator. It knows about all kinds of units and is as simple as typing in plain English.

For example...

Say I have an LED that I want to run from a 12V DC power supply. I already know that the LED requires a forward voltage of 2V and and a forward current of 20 milliamps. What I want to know is how big my current limiting resistor needs to be.

I know I need to drop the voltage by 10 volts, and my draw will be 20 milliamps, so I go to the Google search page and type "10 volts / 20 milliamps" in the search box, hit enter, and out pops my answer... "(10 volts) / (20 milliamperes) = 500 ohms." Woohoo! Now, I've never seen a 500-ohm resistor, so I opt to use a 470-ohm, which is pretty close.

Next I want to build an enclosure for my little project, but I only have measurements in inches, and I want millimeters (because I'm an engineer). This time I type "9 in in mm" and get "9 in = 228.6 millimeters." Great!

To celebrate my project, I decide to bake a cake, but I don't have the correct measuring jug. The recipe says 2 cups, but I can only measure in fluid ounces. No problem, Google calculator has me covered! I type in "2 cups in fl oz" and get my answer "2 US cups = 16 US fluid ounces." Doh! Of course it is, but I'm curious to know what that is in gallons. Now we type "2 cups in gal," and get "2 US cups = 0.125 US gallons."

Now I'm obsessed with gallons and have some time while my cake is baking. I decide to find out how economical my truck is. I know a full tank is about 15 gallons, and I can do about 225 miles before I need to refill. I head over to Google and type "225 miles / 15 gallons," and I'm surprised by the result "(225 miles) / (15 US gallons) = 6.37715558 kilometers per liter." What kind of measurement is that? Never mind. I can specify the units I want the results in. I retry with "225 miles / 15 gallons in mpg" and get "(225 miles) / (15 US gallons) = 15 miles per gallon." Ouch! Hmm, I need a new truck!

Maybe it looks better in different units ... time to try something wacky! This time I tried "225 miles / 15 gallons in mm per fl oz" and got my result: "(225 miles) / (15 US gallons) = 188 595 mm per fl oz." Looks much more impressive now :)

Also, Google calculator does currency conversions: "99 gbp in usd," gives "99 British pounds = 195.2676 U.S. dollars."

You can even do clever stuff like working out what people in the UK pay for gas in your local currency and measurements...
"0.89 gbp per liter in usd per gallon" gives us
"0.89 (British pounds per liter) = 6.64504815 U.S. dollars per US gallon."
Ouch! \$6.64 a gallon is a rip off!