string tension applet

This applet calculates string tensions based on pitch, gauge and type of string. It also does the inverse calculation of string gauges based on pitch, tension and type of string.

NOTE: Use at your own risk! The results of this calculator are not guaranteed to be correct! Different instruments have different abilities to withstand tension and differing responses to various string gauges. Use common sense and your own best judgement at all times.
This calculator is based on string weight data provided by D'Addario Strings. The phosphor bronze, nickel wound, stainless steel and half round string types correspond to D'Addario PB, NW, XSG and HRG strings respectively. The formula for calculating string tension was passed on by Graham McDonald a luthier in Australia. It originally appeared in American Lutherie No 2 June 1985.
Enter the data for each string on a separate line consisting of 3 space delimited values giving the pitch of the string, the gauge or desired tension, and finally the type of string. Once the string data is typed in to the text area, clicking the Calculate button will append the resulting gauge or tension to each line of string data. If further calculations are desired, simply edit the string data and click Calculate again. Old results will be stripped off the end of the data lines and replace with the new ones.

The sample data above is for a standard set of light guage steel acoustic guitar strings. Try clicking Calculate. The first set of data gives gauges and generates resulting tensions. The second gives target tensions and generates gauges. The Metric and Verbose checkboxes will toggle the output units and display of some extra string info.

The pitch of the string may be entered as a note plus octave number, with optional trailing sharp or flat symbols, like so:

C4 A4 F5b D2# g6
A4 is 440hz.

Notes may also be entered ABC style:

C A _f ^D,, g'
A is 440hz.

The second value in the line is either the gauge of the string, if tensions are to be calculated, or the tension of the string if gauges are to be calculated. It is a decimal number followed by a unit of measure, which determines whether the value is a gauge or a tension. The recognized unit suffixes are:

" cm mm - for gauges
# lb kg - for tensions
Note that no spaces are allowed between the number and the unit of measurement. If the unit is omitted, it is assumed to be inches or milimeters, depending on whether the Metric checkbox is checked. Note that if you do not specify the unit of measure, switching between metric and english units effectively changes the gauges. The calculator will report an error if the gauge specified is less than .004".

The final value is the type of string. Recognized string types are:

p pl - plain steel
b pb w - phosphor bronze wound
n nw - nickel wound
s xs - stainless steel wound
h hr - half round wound

The calculator also recognizes line that specify the string length. This is a line beginning with either:

len or
Following this a decimal number followed by a unit of measure is expected. The default length if none is specified is 25.5". Multiple length lines may be entered in the text area, and string specifications reflect the closest preceding length line.

The calculator will display a total of the tensions computed to that point when it finds a line beginning with:

total or
In the second case, the total is multiplied by 2 to account for double strung instrument. Each time a total tension is displayed, the internal sum is reset to 0, so the value only includes tensions subsequent to the previous total displayed.

Remember, you and you alone are responsible for the results of using this calculator.

That said, lightweight guitar string sets have about 23# of tension on the plain strings, 26# on the low E, and 30# on the other wound strings. Medium gauge guitar sets have roughly 26# on the plain, 30# on the low E and 36# on the rest.

Irish bouzouki family instrument generally run at lower tensions, and use a wider range of tensions from one instrument to another, especially as some bouzoukis are quite lightly constructed and can't handle high tensions. A very rough guide might be 16-21# on plain strings and 19-25# on wound, though on any one instrument the tension on the plain and wound strings respectively would generally be about the same.

The D'Addario web site gives string tensions for all of their sets of strings, which are available for a wide variety of instruments. Checking the tensions for an instrument that is similar to yours can give you some idea of where to start tension wise. However, the further your instrument's scale length and tuning is from that indicated by D'Addario, the more you may have to adjust the desired tension to get the sound you want. Also, if your instrument is particularly delicate, you may need to adjust the tensions downward to take that into account.

Another factor to be aware of is that plain strings less than about .010" and wound strings less than .020" will start to break at tensions above 23# or so.

Source code for this applet is hereby place in the public domain, and may be downloaded here. Please keep in mind that this is a very quick and dirty bit of code. :-) Comments are welcome at


dan mcmullen