A CompleteTechnical Reference for Fretted Instrument String Tensions

Modern music has become so sub-divided and fragmented that there is no longer one turn-key string solution for every playing style or desired sound. At one point in time, there were no standardized string gauges, but John D’Addario Sr. changed all that in 1939 with the introduction of light, medium and heavy gauges for acoustic instruments. Throughout most of the 20th century, standardized electric and acoustic guitar gauges were sufficient for needs.  Occasionally, new gauges (often hybrids of existing sets), were created for specific purposes and string offerings from manufacturers became immense. However, today there are so many popular styles and trends that it is often necessary for players to go outside of standard gauge sets to get the effect they desire. Whether it’s open tunings, drop tunings, baritone guitars, 5-string guitars, 7-string guitars or a variety of other reasons, many players are opting to go their own way and customize their string selection and sound.

Why Do You Need To Know About String Tension?
D’Addario receives hundreds of inquiries each year from players who have questions or problems to solve related to string gauges or tensions. To assist players in determining the appropriate string for their needs, we created the Online String Tension Guide, a complete book of charts for determining the appropriate string to be used in just about any situation. The guide includes formulas for determining string tension for any string on any instrument type or scale length using three basic measurements: the Unit Weight, the Scale Length of the instrument, and the Frequency of the string. If scientific formulas aren’t your strong point, we have pitch/tension charts for just about every string we make, including electric guitar, acoustic guitar, classical guitar, and bass guitar.

T (Tension) = (UW x (2 x L x F)2) / 386.4

String Tension Facts and Figures
Before we dig in to examples of how to determine various string tensions, here is a brief summary of what string tension is and what effect it has on your instrument and your playing.

Guitar Fingerboard Layout

Understanding what determines string tension
In order to determine the tension at which a string will vibrate, you need three pieces of information: the Unit Weight, the Scale Length, and the Frequency of the string. You can use the charts in this brochure to get a pre-calculated tension for the D’Addario strings listed or you can use the formulas below to calculate the exact tension for any string using the scale length of your particular instrument. All of the charts illustrate string tensions for each string at a variety of pitches, in case you use alternative tunings.

UW- Unit Weight. In all the charts and formulas in the brochure, unit weight is expressed in pounds per linear inch (lb/in).

L- Scale Length. This is the vibrating length of the string. This is determined by measuring the distance from the nut to the bridge of the instrument in inches (in).

F- Frequency or pitch. This is the pitch at which you will be tuning the string expressed in cycles per second (Hertz).

Below are two fingerboard graphics detailing the various frequencies for the standard guitar and electric bass guitar. To calculate the tension of a string in pounds use the formula below,
inserting the three variables described above:

T (Tension) = (UW x (2 x L x F)2) / 386.4

To convert the result into Newtons, simply multiply by 4.45.

If you know what tension you want the string to have, you can calculate the string unit weight. You can then use the charts in this guide to locate a string with approximately the same desired unit weight.

UW (unit weight) = (T x 386.4) / (2 x L x F)2

String tension is determined by vibrating length, mass, and pitch. The string diameter alone does not determine a string’s tension. By using different raw materials (nickelplated steel or phosphor bronze, etc.) or by varying the ratio between the core and the wrap wire, two strings with the same diameter, tuned to the same pitch, could have two different tensions.

There are many factors other than string gauge that determine the actual and perceived string tension on your instrument:

Scale Lengths

To calculate the exact tension for a string on your instrument, measure the scale length (nut to bridge) of your instrument and then use the formula on the previous page. The following scale lengths were used to determine the string tensions found on the tension charts in this brochure.

  • Acoustic/Electric/Classical Guitar = 25 1/2"
  • Electric Bass Guitar (Superlong Scale) = 36"
  • Electric Bass Guitar (Long Scale) = 34"
  • Electric Bass Guitar (Medium Scale) = 32"
  • Electric Bass Guitar (Short Scale) = 30"
  • Mandolin = 13 7/8"
  • Mandola = 15 7/8"
  • Mandocello = 25"
  • Mandobass = 42"
  • Banjo = 26 1/4" (19 5/8" for 5th string)

• The flexibility of the instrument top and neck.

• The string break-angle at the nut and saddle/bridge.

• String height or “action” as adjusted at the saddle.

• Truss rod adjustment (neck relief).

Note: Before deciding on a string gauge, be sure your instrument is properly “set up.” Unusually high action can change the way the string tension feels and can also result in poor intonation.

How to Measure String Tension
String tension is measured in pounds of pull per string. When all of the tensions of each string are added up, you get the “set tension” for that set. If, for example, you want to change the tuning of one string, you should try to select a string gauge that will offer a similar tension to the string you are replacing, but can be tuned to the desired pitch.


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