If you want the easiest way to transpose (all you know is what key you want to end up in), use this toolhttp://montrealsession.mine.nu/editor.php
- it transposes by semitones, but it simultaneously tells you what key you're transposing to. When I was just learning to transpose for Mountain Ocarina, this was my go-to tool, because even before rendering the music, I could quickly see both by how many semitones I was transposing and whether the key I was about to choose was an "easy" or "hard" key to play in.
However, sometimes you're using a tool that only tells you by how many semitones to transpose.
For example, the converter at http://mandolintab.net/abcconverter.php
will convert your music in abc format to standard musical notation. It also offers a transposition option, but you have to enter how many semitones you want to move up/down. The site does provide "tranposing help" to calculate the number of semitones between your desired keys, which you then enter in the transposition field.
The above online tools were great until midi support disappeared from my Mac web browsers. The app I use now to translate and play music on my Mac desktop, EasyABC, requires me to know by how many semitones I'm moving and doesn't provide any hints by key. To calculate the number of semitones between keys, refer to the attached chart (circle of 5ths).
- by one key, example G to D, transpose up 7 or down 5 semitones
- by two keys, example C to D, transpose up 2 or down 10 semitones
- by three keys, example C to A, transpose up 9 or down 3 semitones
- by one key, example F to Bb, transpose up 5 or down 7 semitones
- by two keys, example C to Bb, transpose up 10 or down 2 semitones
- by three keys, example C to Eb, transpose up 3 or down 9 semitones
If you know a little music theory, read on...
In western music, there are 12 notes: C, C#, D, D#, E, F, F#, G, G#, A, A# e B. A semitone is the smallest musical interval, e.g., between C and C#. There are 12 semitones in an octave. Going up X semitones is the same as going down 12-X semitones, key-wise. So as long as you know how many semitones lie between two adjacent keys on the circle of 5ths chart (either 5 or 7, depending on whether you're transposing up or down), you can figure out using addition/subtraction how many semitones lie between two keys that aren't adjacent.