Stumbled across this nifty web page trying to find an A to tune my mandolin. Exactly what I was looking for:

Online Violin Tuner

This works for both violin and mandolin because they have the same strings (hence why I can play both).

Tuning a mandolin is much more difficult than tuning a violin for me because:

1. I’ve been tuning violins for 13 years, and I’ve tuned a mandolin under 20 times.
2. You tune a violin with a bow, and mandolins don’t have bows.

My ear is trained to tune a violin with only an A. The A string is first tuned to a standard pitch (440 Hz), usually given by the oboe in a full orchestra, or the concert master in a string orchestra. (When playing with an instrument that cannot be tuned easily such as a piano , the violin is tuned to it.) After tuning the A string the other strings are tuned against each other to be perfect fifths by bowing across two at a time. Any string player’s ear is very accustom to tuning in this method.

What makes tuning the mandolin so hard for me is that it is plucked, not bowed, so the tones resonate differently and you cannot pluck two different strings at once to listen to the fifths. Plus, there’s eight strings instead of four. I’m sure I’ll get better with practice and my ear will get used to listening to the plucked tones, but for now it’s hard so this little tuner saved me a lot of trouble.

More about the mandolin: http://en.wikipedia.org/wiki/Mandolin

Bonus Trivia on Violin Tuning: A minutely higher tuning is sometimes employed for solo playing to give the instrument a brighter sound; conversely, Baroque music is sometimes played using lower tunings to make the violin’s sound more gentle.