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WikiProject Mathematics (Rated Start-class, Mid-importance)
WikiProject Mathematics
This article is within the scope of WikiProject Mathematics, a collaborative effort to improve the coverage of Mathematics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
Mathematics rating:
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 Field:  Geometry
One of the 500 most frequently viewed mathematics articles.

other guy

I came to this page to find out about the diameter sign. I believe it's ⌀ (Unicode 2300, looks kind of like ø), as opposed to ∅ (empty set, Unicode 2205, looks kind of like Ø). Maybe one of you math types could mention the diameter sign in the article? -- user:Nate Silva

I'm one of those "math types" and I've never heard of this symbol? In what contexts have you seen it? Michael Hardy 22:27, 11 May 2004 (UTC)

I'm another "math type" and I've never seen or heard of a a"diameter sign" before. Math textbooks don't use it. --Dbenbenn 06:04, 11 Dec 2004 (UTC)

Diameter sign is used mostly on technical drawings (mechanical) to indicate that shape is round, not square. --andrejj 06:56, 11 Dec 2004 (UTC)

I like the way the symbol is explained here, and the mention of the Scandinavian letter as a replacement. Could someone maybe add an explanation that this is NOT exactly the same as the Greek letter "phi"? It's mentioned here:

and in Wikipedia:

Thanks. Marzolian (not logged in) (talk) 00:29, 31 March 2011 (UTC)

I've had some courses in engineering a while ago and have always heard the diameter symbol called "phi". Cosidering that the "source" above never even mentions a "diameter symbol", i'm going to put {{cn}}s on the statements here and at Phi#Use_as_a_symbol. -- Jokes Free4Me (talk) 04:10, 11 February 2012 (UTC)

triple a systems


I am missing a link to the Diameter Computer Protocol (AAA-System). thanks

Definition of a diameter

I have heard that the formal definition of the diameter (for an arbitary closed curve) is that:

A diameter is the locus of mid-points of a set of parallel chords intersecting the curve.

Is it true? If yes, then it should be mentioned in the article. — Ambuj Saxena (talk) 18:04, 22 July 2006 (UTC) s

Chords don't intersect the curve - so what do you mean here? But a definition in one of my maths textbooks was a straight line that is the locus of midpoints of parallel chords. The curve doesn't have to be closed - so for example, parabolas have diameters (parallel to the axis), as do hyperbolas (IIRC, intersecting the centre). By this definition, polygons have a finite set of diameters, e.g. the diameters of a parallelogram are the diagonals and the line segments connecting the midpoints of opposite sides. — Smjg (talk) 23:11, 14 January 2014 (UTC)

Outside of mathematics, "diameter" denotes, not a line, but the greatest distance spanned, usually by a concrete object such as a lesion or a rock. I tried to communicate this following the sentence about the hull in the Generalizations section. Hopefully, there is a clearer way to express this for non-mathematicians. Myron (talk) 10:03, 17 April 2015 (UTC)

Reuleaux polygon

I'm not sure what the definition of diameter of a Reuleaux polygon is but surely it should be mentioned? If it is just the line that goes through the centre then it shouldn't say "the diameter of a circle" but "the diameter of a Reuleaux polygon, and trivially, the circle" or some such, to avoid loss of generality? Triangl 22:54, 16 January 2007 (UTC)

Diameter Symbol

Only in Word

Alt-8960 doesn't work for me Windows-wide. Only gives diameter sign in Word. Not even in Excel. (WXP SP3, Office 2007) —Preceding unsigned comment added by (talk) 00:21, 3 February 2010 (UTC)

Windows-wide ALT code for ø is ALT + 0248. (W7 SP1) -- JoelAlejandro

I have always used ALT + 0216 = Ø Zarboki (talk) 00:38, 27 March 2012 (UTC)

ALT + 0216 is actually a Nordic vowel that looks similar (but not identical) to the diameter symbol. It's probably "good enough" for most people, but it's not quite accurate. Fieari (talk) 14:38, 6 January 2014 (UTC)

According to the W3C[1], the preferred code for Diameter is actually & #8709;. I'm not sure how well this matches up with Unicode. I was unable to get windows to properly type the diameter symbol using any ALT + #### codes. Fieari (talk) 14:38, 6 January 2014 (UTC)

∅ gives the Unicode character U+2205, which is an empty set sign. Whatever the W3C says, using this instead of a diameter sign is no better than using that Nordic vowel as a diameter sign. --Zundark (talk) 18:44, 6 January 2014 (UTC)


I don't know why the perfectly good description of the symbol (which was the bast thing about the article) was removed. I found it Cached in Google and I have put it back. -- —Preceding unsigned comment added by (talkcontribs) 22:44, 1 February 2007

See Help:Reverting for the correct way to restore an earlier version. --Zundark 13:11, 2 February 2007 (UTC)

In fact, diameter is a very contraversial matter to be treated with utmost respect. -—Preceding unsigned comment added by Aes-Sedai (talkcontribs) 10:11 (2 edits), 15 June 2007


I think i understand the language in the "Diameter symbol" section

The symbol or variable for diameter ...

namely that the same character has two purposes, standing for the word diameter, as in

2"⌀ pipe

and also serving as a variable, as in

⌀ = 2"

But it would be better for someone accustomed to regularly using it, as symbol, variable, or (preferably) both, to clean up that paragraph.
--Jerzyt 06:14, 29 February 2008 (UTC)


The Metre article has the British spelling, so why isn't this called diametre? It seems stupid to change into American spelling just because a prefix has been added. --The monkeyhate 17:50, 11 August 2007 (UTC)

The American spelling is also the British spelling. There's no such word as diametre. --Zundark 18:04, 11 August 2007 (UTC)
Is that so? I believe you, but it's rather illogical. --The monkeyhate 19:55, 12 August 2007 (UTC)
Where on Earth did you get the idea that British spelling is logical? You must be from Sweden or something (and hate monkeys). Justice for All (talk) 00:06, 24 October 2008 (UTC)

Measuring instruments use "meter" ie, multimeter, the unit of measure is "metre". Not complicated ;-) Zarboki (talk) 00:36, 27 March 2012 (UTC)

the diameter of the circle (talk) 02:56, 29 March 2009 (UTC)Kiera24.17.137.175 (talk) 02:56, 29 March 2009 (UTC) == Headline text

what is diameter? the essence of a circle that the endpoint outlines.

Symbol is box

How come the symbol is a box for me? I'm using UTF-8. —MC10|Sign here! 03:24, 21 July 2009 (UTC)

Probably because your browser doesn't have access to a font with that symbol in it? See Help:Special characters. —David Eppstein (talk) 03:56, 21 July 2009 (UTC)

Image confusing?


For someone unfamiliar with the meaning, might the image suggest that the diameter only extends to the centre? So I wonder if we should show the diameter line in red (or do something to indicate that more strongly indicates the extent.--A bit iffy (talk) 10:32, 21 August 2011 (UTC)

See current image on main page. John W. Nicholson (talk) 06:19, 7 September 2013 (UTC)

Nuts, bolts, screws

Should not there be a section with different objects like nuts, bolts, and screws which standard measurements are in diameters. — Preceding unsigned comment added by Reddwarf2956 (talkcontribs) 23:36, 24 August 2012 (UTC) All nuts,bolts,and screws should have a diameter.

See Screw thread#Diameters. A the moment, this article ignores real-world uses where different types of diameter are often needed and used. In the case of the transverse section of a screw - across the threaded part itself - this article would have you convinced that only the major diameter is considered. However, the pitch diameter is quite an important consideration to ensure proper fitting of bolts and screws as well as gears. Tomásdearg92 (talk) 12:34, 16 February 2014 (UTC)

⌀ symbol used in engineering drawings and camera lenses

I ended up here as I found an SLR camera lens with "55⌀" on the front rim.

The Ø#Similar symbols section says "The diameter symbol is used extensively in engineering drawings, and it is also seen anywhere that abbreviating "diameter" is useful, such as on camera lenses." Unfortunately, no citations were given though I suspect once a WP:RS is tracked down we can add this to the Diameter article. --Marc Kupper|talk 01:53, 9 March 2016 (UTC)

More specifically for camera lenses that take front filters it is the filter diameter (in millimeters). —David Eppstein (talk) 03:11, 9 March 2016 (UTC)

Definition of "width"

width in dir n
The definition of the "width" of body B in direction in 2 dimensions.

Currently the lead says without a citation

For a convex shape in the plane, the diameter is defined to be the largest distance that can be formed between two opposite parallel lines tangent to its boundary, and the width is defined to be the smallest such distance. [my bolding]

But the lead of our article Mean width gives the definition shown in this diagram—the width is direction-dependent and varies for a given figure, rather than being a minimum for that figure. And that definition fits in with the notion of a curve of constant width—the word "constant" implies that for other curves, the width is not constant over the curve but rather varies over the curve.

Unless I see an objection, I'm going to change this accordingly in this article. Loraof (talk) 20:12, 30 April 2017 (UTC)

All three definitions — direction-dependent width, mean width, and minimum width, are in use. Please do not change it in a way that makes "width" refer only to the direction-dependent version, because it is not true that it is only used that way. The specific source used for this claim doesn't appear to discuss this issue directly, but is most immediately applicable to minimum width. —David Eppstein (talk) 20:37, 30 April 2017 (UTC)
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