I'm glad to know about the Strothers string gauge guide. I can see that the gauge suggestions may be a little on the light side in view of what some folks have said, but it's a good reference to have when you're unsure. Thanks again to everyone for your responses.

There's also a funny paradox at play with this...  

Generally, you use a lighter gauge string to help you tune to a higher note without breaking, and a heavier gauge string to help you tune to a lower note without being floppy. That's why 'bass note strings' are heavier than melody strings.

However, there comes a point at which this can be taken too far.  For example, a super thin .008 string tuned to a high note may actually break because it's so thin, and perhaps a .009 in its place might not break for that same note.  Likewise, if you go to TOO heavy gauge in an effort to attain a real low note, the string will not fit properly in the nut and bridge slots, creating buzzes and becoming difficult to fret.

There's a practical range to work within when trying to balance the three factors that govern this:  1) scale length/VSL  2) note you are wanting to tune to, and 3) string gauge/thickness.  No matter how thin your string, you'll never be able to tune two octaves higher than typical DAdd on a normal sized dulcimer. And no matter how thick your string, you'll never be able to tune a normal sized dulcimer to the same low note you could on an orchestra's standup double bass viol for example.  Stringed instruments are certain sizes for a reason- they are designed to be tuned somewhere within a certain reasonable range of notes for their size.

I used to be mystified about string gauges until I found the Strothers string guide online. Just go to strothers.com and choose string gauge calculator under the dulcimer tab. You just plug in the note you want and the VSL and bang! it gives you a gauge. I think the general feeling is that the gauge suggestions are a little light but this is something that varies from player to player. At least it gives you a place to start. I have also found that through experience, I can judge by feel when I am pushing my luck with a string. As you tune up, just press on the string to feel how much give there is. If it's starting to feel tight, you would be wise to back off.

Hope this helps, Barb

Thanks to everyone for your input. I've made some notes. I realize there are variables, but even guidelines given are helpful. I broke a couple of 9 gauge strings a few months ago but, alas, I can't recall what I was attempting to tune to at the time.

On a 28 or 28.5" scale, I would think .009 and .010 strings would tend to more often break if you try tuning any higher than a high e  (for melody strings).  That's just my own experience.

Too many variables to say definitively.  New strings, a week old, six months old, more?   Never tuned above C or regularly tuned up and down?  Never been tuned above DAA, or regularly tuned up and down?  String vibrating as you tune it, or static?  Tuner gear ratio (high ratios like 1:18 easier on strings than 1:4)?  

I have one customer who plays a 27.5" VSL dulcimer with 0.024, 0.012, 2 x 0.010 string gauges up at F,C,f,f above D,A,d,d on stage and when recording.

https://www.threeleggdmare.com/

There's definitely a balance between pitch, string gauge and scale length.  For a given VSL there will be a physical top pitch and bottom pitch you could reach irrespective of the string gauges you try.  This is because every string has an optimum tension at which it will vibrate the best.  A good way to get an indication of this is to look at other instruments VSLs, such as mandolin or guitar, and compare where their standard string gauges and pitches lay against your dulcimer's VSL.

This does not directly answer your question, but the highest standard tuning that I generally see is EBee.  If you are just playing around, I would purchase multiple sets.  (If you have a guitar center, ask at accessory counter for individual strings at about $1 each.) Then just keep tuning until..."POP!"

I have strings in gauges 9, 10, 12, & 22 and dulcimers with 28 1/2" & 28" VSLs. What is the highest note (i.e. g4) that I can tune EACH of these gauges to without the string being likely to break? Info appreciated!