These charts were built from a 21-string full sized instrument tuned to these keys based on a diagram created by Carol Chang. They are somewhat arbitrary. String tensions had to be adjusted when moving between keys which is not best practice. Your instrument’s length, bridge height, strings, and tension preferences will lead to different distances. Feel free to send your own measurements in and we’ll compile them!
For a chart of specific frequencies, see this Piano Key Frequencies file from Vibrationdata.com. All of the following information assumes you are tuning to a pentatonic scale (5 notes per octave).
Example 21-String in Key of G
1. D6 (1174.7 Hz)
2. B5 (987.77 Hz)
3. A5 (880 Hz)
4. G5 (784 Hz)
5. E5 (659.25 Hz)
6. D5 (587.33 Hz)
7. B4 (493.88 Hz)
8. A4 (440 Hz)
9. G4 (392 Hz)
10. E4 (329.63 Hz)
11. D4 (293.66 Hz)
12. B3 (246.94 Hz)
13. A3 (220 Hz)
14. G3 (196 Hz)
15. E3 (164.81 Hz)
16. D3 (146.83 Hz)
17. B2 (123.47 Hz)
18. A2 (110 Hz)
19. G2 (98 Hz)
20. E2 (82.4 Hz)
21. D2 (73.416 Hz)
Tuning Step by Step
Check bridge placement
Tighten or loosen notes in small increments
Move bridges for fine adjustment
1: Check bridge placement
Bridges need to be placed in a recurring pattern of groups of three and two. This grouping does 4 important things. 1) It gives you a visual cue to remember which string sounds which note, 2) informs you which key the instrument is tuned in, 3) provides the physical space to change keys, and 4) provides a guide for how much to shift the bridges when changing keys.
Deciding where to place bridges can be done two ways. The easiest is to use a table of approximate values, several of which are provided above. Place a bridge according to the chart, put it underneath the string, and continue with this guide. This is especially useful if you rarely or never change keys.
Alternatively, you can set the spacing manually. I highly recommend setting bridge spacing manually. It will give you a greater comfort with your instrument, increase your understanding of keys, their relationships to each other, the bridge placements required to reach them, and, if done properly, minimize the amount of adjustments you will need to make to string tensions when changing keys. A complete guide is at the end of this page as it is its own tuning process. Check it out.
Back to Step 1: For a 21-stringed instrument tuned in the Key of G, you'll want your bridges positioned something like this:
2: Pre-tightening Strings
If the strings are newly strung or you loosened them before arranging the bridges, lift each string above each movable bridge and tighten the string until it touches the bridge. Lifting the string up allows you to tighten and loosen the string without fear of breaking it. Strings break during tuning because tension concentrates around the movable bridge; lifting allows the tention to equalize across the entire string.
Once strings are tight to the bridge tip and resist your lift, it is time to check the pitch.
3: Check pitch
Using your tuning device, check each string's pitch by plucking its right side. The left side is not tuned.
4: Tighten or loosen strings in small increments
Lift the string a small distance above the bridge to balance the string's tension, replace it, and then make the appropriate adjustment using the tuning pins. DO NOT change a string's pitch by more than a half step between lifts. Forcing large changes breaks strings.
5: Move bridges for fine adjustment
Once the pitch is close, say off by 20 cents or less, lift the string and move the movable bridge itself. Move it to the right to increase the pitch, and to the left to decrease pitch.
And there you go! If the temperature changes or you play vigorously enough, you'll have to move the bridges slightly to retune it. Get comfortable with the process. With a little practice you need never fear breaking a string again.
Note: Brand new strings take a few turnings to settle in. Use the tuning wrench to tighten the strings as needed, using the lift technique while keeping the bridges where they are. Once the strings are settled, a process that typically takes 2 weeks of daily turnings, you can resume moving bridges for fine adjustments. If you try to move bridges to settle new strings you'll end up with bridges all over the place.
The Manual or Freehand Method
The goal of setting bridges manually is to produce bridge spacings that allow for easy changing between keys and that have spacings customized for your particular instrument. I highly recommend this. Beyond the benefits to key changing it will also give you a greater comfort with your instrument, increase your understanding of keys, how they relate to each other, and eliminate the need to change string tensions. Set an hour or so aside the first time you do this so that you aren't rushed.
It's best to use this method with strings that have already settled. Brand new strings require frequent tension adjustments and may throw the whole thing off.
There are two key pieces to this method: Making sure the spaces between bridges in a set are roughly equal and using your instrument to determine how much space to put between the sets of 2 and 3 bridges rather than some semi-arbitrary table (…like the ones above).
Identify the range of keys you will need to adjust between. If you are unsure, Tune to B♭. It will give you access to the keys of A, D, G, C, F, and B♭. This guide will assume you are tuning to B♭ when giving specifics.
Place the bridge for String 1 as far to the right as you can while leaving enough space to play. That distance is about 4-5 inches (10-12.7 cm) on full-sized instruments. Tune this to the appropriate note. If you are tuning to the key of B♭, String 1 would be D6.
Place String 2's bridge so that its feet are about 1/4" (6 mm) to the left of Bridge 1's feet. Tune the string to the next pitch (C6).
Place Bridge 3 the same distance from Bridge 2 as Bridge 2 is from Bridge 1. That uniformity of spacing is very important, we'll go over why in a second. Tune String 3 to B♭.
You have completed your first set of 3! Now it's time for the magic.
Take Bridge 3, and after the string is tuned to B♭5 and the string is settled, shift the bridge to the left until it sounds A5. Do not change the string's tension. Move the bridge to change the pitch.
Place the bridge for String 4 to the left of the newly positioned Bridge 3. Leave about as much space between it and Bridge 3 as you left between Bridges 1 and 2. If you've done this correctly you'll now have 2 pairs of bridges separated by a gap, and each bridge is about 1/4" away from its closest neighbor. Make finer adjustment to spacing if you need to. Now tune String 4 to G5
Place the bridge for String 5 about the same distance from Bridge 4 as Bridge 4 is from Bridge 3. Tune String 5 to F5. At this point you'll have a set of 3 bridges, 5,4,3, a gap, and then two bridges, 2 and 1.
Time for more magic.
Move Bridge 5 to the left until it sounds E5. Place Bridge 6 about 1/4" to the left of Bridge 5. Tune String 6 to D5. If you've followed all of these steps correctly you'll have three pairs of bridges.
To test if everything is working, move Bridges 5 and 3 to the right so that you form a set of 2 (Bridges 5 and 4) and a set of 3 (Bridges 3,2,1). Bridge 5 and 4 should have about 1/4" (6mm) between them, and Bridges 3, 2, and 1 should have that same gap between each other. Pluck each of the 5 strings. Do they sound the correct notes? If yes, congratulations, you did it! If not, don't give up hope, it can take a few tries to get everything working just right.
If the strings aren't sounding right either the strings weren't settled or your spacing is off. Double check that bridges in sets have the same distance between each other, tune the strings to what they should be, shift bridges 3 and 5 left until they sound their new notes, check spacings again, then move the bridges back and recheck their pitch.
Repeat steps 2-9 for the rest of the strings. Pay special attention to having uniform spaces between bridges and appropriate gaps between sets of 3 and 2. There are a few things to keep in mind: If you are tuning to a key other than B♭ to start, your groupings of three and two will be different, and the pitches you are tuning to and changing to will be different. Write those down ahead of time, otherwise it will be easy to get confused. Visually, remember that the key string, (D in key of D, F in key of F) is always the lowest string in the set of three.
The spacing between bridges in sets will get wider as you move down the instrument. Strings 15, 16, 17 etc. will have way more than 1/4" between their feet- more like 2”. You'll just need enough space both to make fine tuning adjustments and to accommodate the larger space the bass strings need to change pitch. Also, the length of your particular instrument, height of the movable bridges, and your personal preference for string tensions will cause some variance to these numbers. You'll have to find what works for your particular instrument. Look at the tuning tables above to get an idea of what you are shooting for.
Once your instrument is tuned up you'll find it easier to shift between keys and to identify individual strings. Good luck and have fun!