Notes on Guitar String Tension

Let's face it: most folks don't spend too much time thinking about the effects of tension on their instruments and many people are confused by advertising terms associated with picking guitar (or any instrument) strings. That's why so many players often use "medium" strings with the idea that they're in the middle of the pack for string tension at standard pitch rather than, basically, extra heavy. And have you ever wondered why, given the same setup on two instruments, the stiffness of each instrument will feel different? Well, I'm going to get to that stuff in this quick-ish primer.

First let's talk about scale length and how it effects tension. I'm going to write this using steel string guitar as a reference, but the concepts carry over to just about any fretted (or bowed) instruments. I'll use this excellent tension calculator (click for link) for the figures.

Let's compare overall tension between several common scale lengths using an average American light gauge (54w-12) set of strings. 

Old Kay scale (25.875"): 171 lb

Martin scale (25.4"): 165 lb

National scale (25"): 160 lb

Gibson scale (24.75"): 156 lb

Parlor scale (24"): 147 lb

Do you see how shortening the scale length removes a lot of tension given the same strings? There's 10 lb of difference between a standard Martin and a standard Gibson and you'll certainly feel that in your left hand at the end of a gig. That extra tension also needs to be accounted for when the guitars are being designed for long-term use.

Now let's see what happens when you string the same scales with a medium set...

Old Kay scale (25.875"): 190 lb

Martin scale (25.4"): 184 lb

National scale (25"): 178 lb

Gibson scale (24.75"): 174 lb

Parlor scale (24"): 164 lb 

Yikes! They all jumped 20 lbs! It's no surprise (when you've crunched the numbers) to find that many of those funky old long-scale poplar Kay necks have all pretty much warped or twisted after decades of being strung with mediums. Ones that were gauged lower held up, unsurprisingly, much better. The same rule of thumb applies to long scale Martins as well but to a lesser extent.

My favorite suggestion to newer players is to try to get used to sets of "custom light" or "11s" rather than regular "lights" (which are gauged more like a true "medium" in the tension scale) as your average guitar player probably owns a Martin-style, long scale dreadnought-type instrument rather than something shorter scale and thus "more comfortable" with regular "12s" or lights.

Here are the tension figures for an average set of 11s:

Old Kay scale (25.875"): 150 lb

Martin scale (25.4"): 144 lb

National scale (25"): 140 lb

Gibson scale (24.75"): 137 lb

Parlor scale (24"): 129 lb

Compared to a set of 12s, you're decreasing tension about 20 lbs. On something like a Martin this is quite dramatic. Personally, I mix gauges from both a set of 12s and a set of 11s to make the "perfect" set which is lighter on the wound strings and heavier on the plains.

Why the heck would I do that? Because a standard string set is actually quite "unbalanced" tension-wise and I really can't stand the way that "plays" up the neck. Let's look at single string tension differences to see why. Below are string to string calculations for Martin scale length and a standard set of 12s:

E 54w: 27.26 lb

A 42w: 28.25 lb

D 32w: 29.79 lb

G 24w: 33.04 lb

B 16p: 23.25 lb

E 12p: 23.12 lb

If you wanted to "balance" the set but retain the feel of the 12 and 16 highs (my personal preference for the two plain strings as they're neither too stiff nor too slack on most scales) you'd have to change your gauges to something that simply is not available in most standard string sets:

E 50w: 23.34 lb

A 38w: 23.28 lb

D 28w: 24.00 lb

G 20w: 24.42 lb

B 16p: 23.25 lb

E 12p: 23.12 lb

Guess what? This altered "light" set comes in at 141 lb overall which is even a touch lighter than your average set of 11s. This is very close to my own personal set except usually I step the A, D, and G strings up 2 values so I can mix and match from strings I have on hand more often.

That begs the question, though: what would a "balanced" medium set look like?

E 54w: 27.26 lb

A 40w: 25.98 lb

D 30w: 26.18 lb

G 22w: 31.59 lb

B 17p: 25.98 lb

E 13p: 26.38 lb

Despite the higher-tension 22w G string (the G is always at more tension than anything else), this set plays on the high end like a snappy, soulful medium set but has comfort for closed-position chords on the low end. This is all at a tension that comes in around the same as the "unbalanced" regular set of 12s: 163 lb overall.

So: what the heck? Why do we play unbalanced sets?

Part of it is the historical appeal: that's the way things were gauged out in the past. Part of it is also appeal to "folk" acoustic players who wail lead picking lines on their lower wound strings and think they need a lot of presence and snap especially on the D&G strings (the ones that break the most, too, due to their abnormally high tension in a standard set).

For most players these unbalanced sets are terrible for an acoustic guitar's most usual role: chordal rhythm playing whether fingerpicked or flatpicked. If you're someone who plays chords all around the neck of your guitar, a balanced set is an absolute must and something you should definitely try out. You will notice a lot less fatigue during a night of playing.

But wait, what if you're a player who uses different tunings?

Oh, man, do I need to address that? Here's what open D tuning does to a standard set of 12s at Martin scale:

D 54w: 21.65 lb

A 42w: 28.25 lb

D 32w: 29.79 lb

F# 24w: 29.44 lb

A 16p: 18.46 lb

D 12p: 18.35 lb

Versus in standard pitch...

E 54w: 27.26 lb

A 42w: 28.25 lb

D 32w: 29.79 lb

G 24w: 33.04 lb

B 16p: 23.25 lb

E 12p: 23.12 lb

The slackened strings drop by ~5lb each! No wonder your truss rod might need a light "release" to keep up and perhaps you've noticed your plains feel flabby? It's like you've stepped down to a set of 11s rather than 12s.

The solution, if you plan to use this tuning on said guitar, is to step up the gauges that've been slackened.

Borrowing a 13p, 17p, and 56w from a regular set of mediums and swapping them in place of the high D, A and low D strings is one way to do it but those strings will still be more slack compared to the other strings. Even better would be to use a 14p, 18p, and 58w to replace the same strings. I never suggest upping the G string if you can help it: why stack on more tension when it's already, generally, too tense?

The same rule of thumb applies to other open tunings: if you've detuned the string by a step you can generally upgrade the string 2-4 values safely to compensate for the lowered tension of the lower pitch.

However, if your tuning is higher than normal you definitely need to gauge down or havoc may ensue. Take a look at open E on a standard set of 12s at Martin scale:

E 54w: 27.26 lb

B 42w: 35.60 lb

E 32w: 37.53 lb

G# 24w: 37.09 lb

B 16p: 23.25 lb

E 12p: 23.12 lb

Upping that tuning adds a lot of tension -- it's now about 184 lb vs. standard "12s" tension of  165 lb. That's basically "stringing" the guitar with mediums while it's strung with 12s. The way to correct for that is by stepping the gauges down for raised strings. For every step up I suggest reducing by 4 values. For example the low A raised to a B from a light set should be a 38w rather than a 42w to maintain the same tension (or close to it) as it was when tuned lower.

Anything else? Experiment. Be aware that even 10 lb tension changes will often effect your guitar's setup, sound and feel. And, if unsure how to solve tension inconsistencies, get scientific and use the calculator. I use it all the time to help customers arrive at personal playability solutions.