Pipe length, "feet" and pitch


The pitch of an organ stop is still indicated by feet. As in all wind instruments the pitch produced by a pipe depends on the length of the pipe, i.e. the length of the resounding column of air.
The longer the pipe, the deeper the pitch and vice versa.

  • The point of reference for all specifications is the lowest pitch on the manual or pedal, the low C with a frequency of 64 Hz (i.e. 64 oscillations per second as compared to the "concert pitch a" with 440 oscillations per second).

  • In order to produce this pitch, the pipe needs to be about 2.4 meters long. Pipe length is not indicated in meters, though, but in feet. So the largest pipe producing a low C measures 8' equalling 240 cm. The 8' is also called the "normal pitch" or "equal pitch" which means that an 8' organ stop, that is, an 8' row of pipes will produce the same normal pitches as the same keys would produce on the piano.

  • Of course not all pipes of an 8' stop have the same length, or else they would all sound at the same pitch, but with progressive pitch the pipe will be shorter. There is a simple rule saying that if the length of the pipe is halved the pitch will be doubled, that is it will have double frequency. This means that the pipe sounding an octave above low C is only half as long, 4' or 1.2 m, the one another octave higher will be 2' or 60 cm and so on. The same obviously applies in the other direction as well: the pipe producing the C an octave below would measure 16' (4.8 m) etc. Actually, the pipes are even longer as indicated as the foot of the pipe and a reserve (invisible cut at the back of the pipe that can be raised or lowered) to be flexible in tuning are not included. So, in effect an 8' pipe would be about 2.8 m (9'4").

  • Now each stop is named after the length of its longest pipe, i.e. its lowest pitch, so that a 4' stop would sound an octave higher than an 8' stop, a 16' stop one octave lower and a 32' stop two octaves lower which is already the lowest frequency the human ear is able to hear, 16 Hz. The highest key of a 1', the c'''' will produce about 16,000 Hz, the highest pitch the ear can hear. So the organ is the only musical instrument that covers the whole range of pitches man can hear. Due to the enormous size of a 32' stop - the largest pipe measuring a total of about 11 m (see picture on the right) - these stops are only found in very large instruments, very few organs even have a 64' stop. As the amount of 32' and 64' stops have a decisive influence on the size and sound of an organ I included these details in the charts.

  • The fact that an organ can produce different timbres is due to the fact that the timbre depends on the harmonics. This means you can change the timbre by adding stops in other pitches (lengths). So actually pipe organs basically do not work any different from synthesizers. The more stops rich in harmonics are added to the 8' basis the lighter and the more colorful the sound will be.

  • There are not just stops in octave pitch levels (32' - 16' - 8' - 4' - 2' - 1' - 1/2' etc.), the organ uses almost the whole series of harmonics, especially
    - fifths (these are the "thirds", that is, 32/3 = 10 2/3', 16/3 = 5 1/3', 8/3 = 2 2/3', 4/3 = 1 1/3', 2/3' etc.)
    - thirds (the "fifths", that is, 32/5 = 6 2/5', 16/3 = 3 1/5', 8/5 = 1 3/5', 4/5' etc.)
    - sevenths (the "sevenths", that is, 32/7 = 4 4/7', 16/7 = 2 2/7', 8/7 = 1 1/7', 4/7' etc.
    - ninths (the "ninths", that is, 32/9 = 3 5/9', 16/9 = 1 7/9', 8/9', 4/9' etc.

    You maybe wondering why "Quints" – which are the fifth note of the musical scale – are measured as "thirds" and Tierces – which are the third note of the musical scale – are measured as "fifths". The explanation is the physical structure of the harmonic series that has nothing to do with the musical scale. The harmonic series is set up as follows - (shown with an 8'-stop in this example):

    • 1st harmonic = "first": 8/1' = 8' (unison)
    • 2nd harmonic = "half": 8/2' = 4' (octave)
    • 3rd harmonic = "third": 8/3' = 2 2/3' (quint)
    • 4th harmonic = "quarter": 8/4' = 2' (octave)
    • 5th harmonic = "fifth": 8/5' = 1 3/5' (major tierce)
    • 6th harmonic = "sixth": 8/6' = 1 1/3' (quint)
    • 7th harmonic = "seventh": 8/7' = 1 1/7' (minor seventh)
    • 8th harmonic = "eighth": 8/8' = 1' (octave)
    • 9th harmonic = "ninth": 8/9' = 8/9' (major ninth)
    • 10th harmonic = "tenth": 8/10' = 4/5' (tierce)
    • 11th harmonic = "eleventh": 8/11' = 8/11' (fourth)
    • 12th harmonic = "twelfth": 8/12' = 2/3' (quint) - and so on...

    So a V-rangs-Cornet based on 8' with the standard composition 8'-4'-2 2/3'-2'-1 3/5' amplifies exactly the natural harmonic series.
  • Some organ stops only need half the length in order to produce the same pitch, they are called "gedeckt" or "stopped" because they have a stopper in the top that causes the air column to appear to be twice as long. The intensity of the tone is diminished by this, though. On the other hand, there are stops that need double the length, e.g. the high-pressure stops. Of course tone intensity is enhanced here. For more information see The variety of organ pipes and stops.


The keys marked red on the keyboard below indicate the pitch that you will actually hear if you press the low C for a stop termed a certain length:
Octave 4'

 Super Octave 2'


Apart from the stops with just one pipe sounding per note there are also those stops where pressing a key will lead to several tones (usually some of the overtones) sounding. These stops are termed Mixtures. Again, the keys marked red indicate the pitches you will hear when pressing the low C:

Sesquialtera II rks. (2 2/3' + 1 3/5', 12th and 17th)

 Mixture IV rks. (2 2/3' + 2' + 1 1/3' + 1', quints and octaves)



Here's a survey of all usual foot numbers, pitches and their name in different languages:

German Anglo-American French Italian Spanish Number Manual Pedal
Sub-Sub-Oktave 32 64
Sub-Sub-Quinte 21 1/3 42 2/3
Sub-Oktave 16 32
Sub-Terz 12 4/5 25 3/5
Sub-Quinte 10 2/3 21 1/3
Grundton Unison I 8' 16'
(Groß-) Terz Third (Grande) Tierce Terza Tercia III 6 2/5 12 4/5
Quinte Fifth (Grande) Quinte Quinta Quinta V 5 1/3 10 2/3
Septime Seventh (Grande) Septième Settima Séptima VII 4 4/7 9 1/7
Oktave Eighth Octave Ottava Octava VIII 4 8
(Groß-) Terz Tenth (Grande) Tierce Decima Décima, Desena X 3 1/5 6 2/5
Quarte Eleventh XI 2 10/11 5 9/11
Quinte Twelfth Quinte Duodecima, Decimaseconda Docena, Dotzena XII 2 2/3 5 1/3
Sexte Thirteenth XIII 2 6/13 4 12/13
Septime Forteenth Septième Séptima XIV 2 2/7 4 4/7
(Super-) Oktave Fifteenth (Super-) Octave Decimaquinta Quincena, Quinzena XV 2 4
None Sixteenth Novena XVI 1 7/9 3 5/9
Terz Seventeenth Tierce Decimasettima Decisetena XVII 1 3/5 3 1/5
Quarte Eighteenth XVIII 1 5/11 2 10/11
Quinte Nineteenth Quinte Decimanona Decinovena XIX 1 1/3 2 2/3
Sexte Twentieth XX 1 3/13 2 6/13
Septime Twenty-First Septième Vigesimaprima Séptima XXI 1 1/7 2 2/7
Superoktave Twenty-Second (Super-) Octave Vigesimaseconda Veintidocena, Vintidotzena XXII 1 2
None Twenty-Third Vigesimaterza Novena XXIII 8/9 1 7/9
(Klein-) Terz Twenty-Forth Tierce Vigesimaquarta XXIV 4/5 1 3/5
Quarte, Undezime Twenty-Fifth Vigesimaquinta XXV 8/11 1 5/11
(Klein-) Quinte Twenty-Sixth Quinte Vigesimasesta Veintiseisena XXVI 2/3 1 1/3
Sexte Twenty-Seventh Vigesimasettima XXVII 8/13 1 3/13
Septime Twenty-Eighth Septième XXVIII 4/7 1 1/7
Oktävlein Twenty-Ninth (Super-) Octave Vigesimanona Veintinovena XXIX 1/2 1
(Klein-) Terz Thirty-First Tierce Trigesimaprima XXXI 2/5 4/5
(Klein-) Quinte Thirty-Third Quinte Trigesimaterza XXXIII 1/3 2/3
Septime Thirty-Fifth Septième Trigesimaquinta XXXV 2/7 4/7
Oktävlein Thirty-Sixth (Super-) Octave Trigesimasesta XXXVI 1/4 1/2
(Klein-) Terz Thirty-Eighth Tierce XXXVIII 1/5 2/5
(Klein-) Quinte Fortieth Quinte XL 1/6 1/3
Oktävlein Forty-third (Super-) Octave XLIII 1/8 1/4


This could probably be interesting too: Dictionary of organ stops in ten languages