If you’re like me, when you play a song in different tunings (especially ridiculously low tunings), you can’t always go as low as you can because of string gauge or scale limitations. I play a lot of low-tuned stuff, especially thall, and those tunings are crazy.
Whenever I tune down, sometimes I’ll have a guitar that is, say, in Drop D or Drop C tuning. Instead of messing with my intonation, I’ll use a pitch shifter to tune down instead. Pitch shifters like the Digitech Drop (an awesome polyphonic drop pedal) allow you to go down a whole octave.
I created a spreadsheet of drop tunings based on base tunings you can quickly reference to download for free here.
You can see that you choose your base tuning and then follow it across to determine how many semitones to go down. For example, if you’re in Drop D and want to go down to Drop A, you would see you go down 6 semitones.