Definitions

Manual
A keyboard played by the hands.  All instruments on this list also have a pedalboard, which is the keyboard played by the feet.
Rank
A set of pipes of a particular tone color, one for each note of the keyboard.  Usually there are 58 to 61 pipes for a rank used by the manuals, and 30-32 for a rank used by the pedals.
Stop
A knob or tab on the organ console that turns on a set of pipes.  If no stops are turned on, pressing a key on the keyboard will not make a sound.
Register (Independent Stop)
An independent speaking stop that has its own pipes that are not "borrowed" from any other stops.  A register is made of one or more ranks.  For example, a single rank of Trumpet pipes would be counted as one register, but a Mixture IV would also be counted as one register despite having 4 ranks.  See "Borrowed Stop" below for another example.
Borrowed Stop
A stop that does not have its own pipes, but rather reuses pipes from an independent stop (register).  For example, a unit flute rank might be comprised of 85 pipes and be available to the organist as a 16' stop, an 8' stop, and a 4' stop.  This flute would be counted as one rank and one register, but would appear in the stoplist three times.  One stoplist entry would be counted as an independent stop, and the other two would be counted as borrowed stops.  This is usually denoted in a specification by labelling the stop as being extended from a different stop, and only 12 pipes will be listed, the extension which allows the stop to appear at the higher or lower pitch.
Total Stops
The total number of speaking stops on the organ, whether independent or borrowed.

Footnotes:

1. Atlantic City Convention Hall -- Originally, it was claimed that this instrument had 455 ranks and 33,112 pipes.  However, according to an article written in The American Organist [1989? 1990?], these numbers had not been substantiated, and only 336 ranks had been found.  This article also stated that due to many factors, including a flood, entire divisions sealed off because of asbestos in the chamber, etc., the organ had never been 100% operational.
More recent research by Stephen D. Smith indicates that the instrument actually has 449 ranks, and between 32,000 and 33,000 pipes, forming 336 independent stops, which are borrowed to form 852 stoptabs (excluding percussions and accessories) on the console.  His research also indicates that most of the instrument was present and operational when it was dedicated.
This then brings up the continuing question of which instrument is "larger" -- Wanamakers, or Atlantic City?  Since I have chosen somewhat arbitrarily to sort this list by number of ranks, Wanamakers obviously ends up on top; but if sorted by number of pipes, Atlantic City would win.  However, Wanamakers is today mostly operational, and is undergoing a complete restoration that will return it to complete working condition.  Atlantic City, sad to say, only has about 150 ranks operational, and has had no resources allocated for a restoration.  Therefore, I have numbered them both as #1, but listed Wanamakers first.  Let's hope that someday Atlantic City will also be restored to full operation so that there can once again be some competition for the largest operational pipe organ!
2. First Church of Christ, Scientist -- A Christian Science publication describes the organ as 237 ranks, 13,595 pipes, but only mentions revisions made in 1979. The revisions to bring the instrument to 238 ranks may account for the differing pipe count listed.
3. The instruments with less than 200 ranks are recent additions, and I probably have missed some that belong in here.  Please forward any corrections to me as soon as possible (email address embedded on main page to deter spam)!  I'm trying to limit my additions to instruments that at least as large in some measurement as the smallest instrument currently on the list.  I think there are enough that fit in that category that it will take me a while to find them all.  But feel free to send me any others if they're close to that size or are particularly famous.
4.  I have only been able to find conflicting reports about the Liverpool Anglican Cathedral organ.  An intial report I was sent said 150 ranks, but I think that is more likely the stop count, not a rank count.  Another report said that it had 188 ranks with 149 stops, while a third said 185 ranks.  I found two stoplists for this instrument, both of which seem to indicate that it has between 181 and 184 ranks (assuming no borrowing), making it the largest organ in the United Kingdom.  This agrees with a statement to that effect on the official Royal Albert Hall website.  Does anyone have an up-to-date spec sheet that indicates borrowing, or more accurate pipe and rank counts?

History

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