# Who decided, and when , that a right angle was 90 degrees ?
**URL:** https://boards.straightdope.com/t/who-decided-and-when-that-a-right-angle-was-90-degrees/648839
**Category:** Factual Questions
**Created:** [January 30, 2013, 10:00pm UTC](https://boards.straightdope.com/t/who-decided-and-when-that-a-right-angle-was-90-degrees/648839 "2013-01-30T22:00:24Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@Bones\_Daley](https://boards.straightdope.com/u/Bones_Daley)
#### Post date: [January 30, 2013, 10:00pm UTC](https://boards.straightdope.com/t/who-decided-and-when-that-a-right-angle-was-90-degrees/648839/1 "2013-01-30T22:00:24Z")
Probably the Greeks or Egyptians, I dunno, but whatever, the dude that decided on 90 degrees couldn’t have given the matter much thought.
Like, 90 is divisible by, 2, 3, 5, 9 , 10 , 15, 30 and 45. What use is that ?
Now imagine if the dude had decreed, “we’re going to have 120 degrees in a right angle …” …WOW …
Straight off, the right angle is divisible by 2,3,4,5,6,8, 10, 12,15,20, 30, 40 and 60. Only problem is that it ain’t divisible by 9 …well DUH …
How cool is that ?
Is there any valid reason why the international standards body couldn’t still adopt this concept ?
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### Author:  [@Yorikke](https://boards.straightdope.com/u/Yorikke)
#### Post date: [January 30, 2013, 10:04pm UTC](https://boards.straightdope.com/t/who-decided-and-when-that-a-right-angle-was-90-degrees/648839/2 "2013-01-30T22:04:20Z")
Nobody decided that a right angle was 90 degrees. The concept of 90 degrees was named “right angle.” It is what it is. I suppose there could be a calculus in which a circle is 720 degrees. Far out.
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### Author:  [@Smeghead](https://boards.straightdope.com/u/Smeghead)
#### Post date: [January 30, 2013, 10:05pm UTC](https://boards.straightdope.com/t/who-decided-and-when-that-a-right-angle-was-90-degrees/648839/3 "2013-01-30T22:05:18Z")
Are you asking why the word “right” is used to describe it, or why it’s divided up into 90 degrees? I think it’s the latter. That was thanks to the Babylonians, who divided up a circle into 360 degrees. It was the ability to divide up 360 lots of different ways that they liked. The 90 degree thing was just a side effect.
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### Author:  [@Inner\_Stickler](https://boards.straightdope.com/u/Inner_Stickler)
#### Post date: [January 30, 2013, 10:07pm UTC](https://boards.straightdope.com/t/who-decided-and-when-that-a-right-angle-was-90-degrees/648839/4 "2013-01-30T22:07:04Z")
Just divide your circles into 480 degrees and your right angles will be 120 degrees.
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### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [January 30, 2013, 10:08pm UTC](https://boards.straightdope.com/t/who-decided-and-when-that-a-right-angle-was-90-degrees/648839/5 "2013-01-30T22:08:05Z")
I think the question here is “why is the circle divided into 360 degrees, rather than some other number of divisions?”
(not “why is a right angle square?”)
ETA: dammit - took too long composing that.
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### Author:  [@OldGuy](https://boards.straightdope.com/u/OldGuy)
#### Post date: [January 30, 2013, 10:10pm UTC](https://boards.straightdope.com/t/who-decided-and-when-that-a-right-angle-was-90-degrees/648839/6 "2013-01-30T22:10:50Z")
The Babylonains divided the circle into 360 degrees. Apart for the divisibility reasons stated, I suspect that the year having 365 days is not a complete coincidence.
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### Author:  [@Inner\_Stickler](https://boards.straightdope.com/u/Inner_Stickler)
#### Post date: [January 30, 2013, 10:11pm UTC](https://boards.straightdope.com/t/who-decided-and-when-that-a-right-angle-was-90-degrees/648839/7 "2013-01-30T22:11:27Z")
Because all the really influential mathematical texts in western civilization have used 360 degrees.
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### Author:  [@Senegoid](https://boards.straightdope.com/u/Senegoid)
#### Post date: [January 30, 2013, 10:23pm UTC](https://boards.straightdope.com/t/who-decided-and-when-that-a-right-angle-was-90-degrees/648839/8 "2013-01-30T22:23:38Z")
Then, there are all those crazies who decided that a full circle should consist of 6.28318531 (approximately) angular units.
I mean, would it fly if we had 6.28318531 inches to the foot? Or 6.28318531 ounces to a pound?
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### Author:  [@FuzzyOgre](https://boards.straightdope.com/u/FuzzyOgre)
#### Post date: [January 30, 2013, 10:34pm UTC](https://boards.straightdope.com/t/who-decided-and-when-that-a-right-angle-was-90-degrees/648839/9 "2013-01-30T22:34:14Z")
It is a right angle, not “The Correct Angle”. Mathematicians use words differently.
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### Author:  [@Kobal2](https://boards.straightdope.com/u/Kobal2)
#### Post date: [January 30, 2013, 10:35pm UTC](https://boards.straightdope.com/t/who-decided-and-when-that-a-right-angle-was-90-degrees/648839/10 "2013-01-30T22:35:36Z")
The question is nonsense, NONSENSE ! A right angle isn’t 90°. It’s π/2 radians.
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### Author:  [@Fubaya](https://boards.straightdope.com/u/Fubaya)
#### Post date: [January 30, 2013, 10:42pm UTC](https://boards.straightdope.com/t/who-decided-and-when-that-a-right-angle-was-90-degrees/648839/11 "2013-01-30T22:42:48Z")
Left angles don’t come out right if you use anything other than 90 degrees for the right angle.
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### Author:  [@DrCube](https://boards.straightdope.com/u/DrCube)
#### Post date: [January 30, 2013, 10:52pm UTC](https://boards.straightdope.com/t/who-decided-and-when-that-a-right-angle-was-90-degrees/648839/12 "2013-01-30T22:52:20Z")
> [@Senegoid](#):
>
> Then, there are all those crazies who decided that a full circle should consist of 6.28318531 (approximately) angular units.
>
> I mean, would it fly if we had 6.28318531 inches to the foot? Or 6.28318531 ounces to a pound?
No, but it flies with circles. If your circle was 12 inches around, would it fly that the diameter was 3.81972… inches? Of course, if your diameter is one inch, it doesn’t help that there are an integer number of degrees in a circle when your circumference is 3.141592… inches.
Irrational numbers are a fact of life with circles. Might as well make that plainly obvious with 2\*pi radians, and simplify all the math while you’re at it.
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### Author:  [@friedo](https://boards.straightdope.com/u/friedo)
#### Post date: [January 30, 2013, 10:53pm UTC](https://boards.straightdope.com/t/who-decided-and-when-that-a-right-angle-was-90-degrees/648839/13 "2013-01-30T22:53:15Z")
> [@Kobal2](#):
>
> The question is nonsense, NONSENSE ! A right angle isn’t 90°. It’s π/2 radians.
You mean τ/4 radians.
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### Author:  [@standingwave](https://boards.straightdope.com/u/standingwave)
#### Post date: [January 30, 2013, 10:55pm UTC](https://boards.straightdope.com/t/who-decided-and-when-that-a-right-angle-was-90-degrees/648839/14 "2013-01-30T22:55:45Z")
100 grads in a right angle. You know it’s right, because it’s metric.
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### Author:  [@aceplace57](https://boards.straightdope.com/u/aceplace57)
#### Post date: [January 30, 2013, 11:07pm UTC](https://boards.straightdope.com/t/who-decided-and-when-that-a-right-angle-was-90-degrees/648839/15 "2013-01-30T23:07:44Z")
A lot of geometry would get screwed up if there were no 90 degree angles.
Equilateral, Isosceles and Scalene triangles. Acute, Obtuse and Right triangles. We studied those for weeks. There’s always 180 degrees in any triangle.
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### Author:  [@Kobal2](https://boards.straightdope.com/u/Kobal2)
#### Post date: [January 30, 2013, 11:07pm UTC](https://boards.straightdope.com/t/who-decided-and-when-that-a-right-angle-was-90-degrees/648839/16 "2013-01-30T23:07:46Z")
> [@standingwave](#):
>
> 100 grads in a right angle. You know it’s right, because it’s metric.
Right, but unAmerican.
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### Author:  [@cmyk](https://boards.straightdope.com/u/cmyk)
#### Post date: [January 30, 2013, 11:19pm UTC](https://boards.straightdope.com/t/who-decided-and-when-that-a-right-angle-was-90-degrees/648839/17 "2013-01-30T23:19:04Z")
Radians, it’s the right thing to do, and the right way to do it.
/Wilford Brimley
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### Author:  [@Canadjun](https://boards.straightdope.com/u/Canadjun)
#### Post date: [January 30, 2013, 11:19pm UTC](https://boards.straightdope.com/t/who-decided-and-when-that-a-right-angle-was-90-degrees/648839/18 "2013-01-30T23:19:50Z")
> [@aceplace57](#):
>
> There’s always 180 degrees in any triangle.
provided you are using Euclidean geometry.
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### Author:  [@johnpost](https://boards.straightdope.com/u/johnpost)
#### Post date: [January 30, 2013, 11:20pm UTC](https://boards.straightdope.com/t/who-decided-and-when-that-a-right-angle-was-90-degrees/648839/19 "2013-01-30T23:20:07Z")
Angus Right the famous mathematician.
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### Author:  [@Duckster](https://boards.straightdope.com/u/Duckster)
#### Post date: [January 30, 2013, 11:32pm UTC](https://boards.straightdope.com/t/who-decided-and-when-that-a-right-angle-was-90-degrees/648839/20 "2013-01-30T23:32:10Z")
Observing just how many degrees of separation there are among the responses so far …
If we limit it to three degrees, we can just sing about it. Increase it to six and we can make a movie or play. Or just ask Kevin Bacon.
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