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#### mike1123

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I know you measure diagonally on a 4:3 screen, but how do you measure the screen size of a 16:9 screen? Thanks. ·
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Same way.

#### RandyWalters

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Quote:
 Originally Posted by mike1123 I know you measure diagonally on a 4:3 screen, but how do you measure the screen size of a 16:9 screen? Thanks. On a 4:3 screen you're supposed to measure diagonally from lower left to upper right. But on a 16:9 screen you're supposed to measure from upper left to lower right. #### DonoMan

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Quote:
 Originally Posted by RandyWalters On a 4:3 screen you're supposed to measure diagonally from lower left to upper right. But on a 16:9 screen you're supposed to measure from upper left to lower right.
Damn! I've been doing it wrong!

#### SteveTiilikainen

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Here are some equations:

w = width; h = height; d = diagonal (all in inches)

"x^2" = "x squared"

"sqrt( x )" = "square root of x"

Finding out what the diagonal of a screen is quite easy if you know the width and height:

1. w^2 + h^2 = d^2

2. d = sqrt(w^2 + h^2)

The easiest example is of a TV that is 4" wide by 3" high:

d = sqrt(4^2 + 3^2)

d = sqrt(16 + 9)

d = sqrt(25)

d = 5"

Let's say you want to find out how wide and tall a 60" widescreen set is (not, of course, including the size of the cabinet).

1. w^2 + h^2 = d^2 (Pythagorean theorem)

2. w = h * 16/9 (a 16:9 set is sixteen ninths wider than it is tall)

3. h = w * 9/16 (contrapositive of 2.)

4. w^2 + (w * 9/16)^2 = 60^2 (by substitution)

5. w^2 + w^2 * 9^2/16^2 = 60^2

6. w^2 * (1 + 9^2/16^2) = 60^2

7. w^2 * (16^2/16^2 + 9^2/16^2) = 60^2

8. w^2 * (9^2 + 16^2)/16^2 = 60^2

9. w^2 = 60^2 * 16^2 / (9^2 + 16^2)

10. w = sqrt(60^2 * 16^2 / (9^2 + 16^2))

Now it's just number-crunching:

11. w = sqrt(3600 * 256/337)

12. w = 52.29"

13. h = 52.29" * 9/16 = 29.41" (from 3.)

14. 52.29^2 + 29.41^2 = 60^2 (checking our work...)

15. 2734.24 + 864.95 = 3599.19

16. sqrt(3599.19) = 59.99 =~ 60 (we're in the ballpark)

So, from 10. and 3., we can infer:

The width/height of a 16:9 display:
w = sqrt(d^2 * 256/337)

(from: w = sqrt(d^2 * 16^2/(9^2+16^2)))
h = w * 9/16

For 4:3 displays:
w = sqrt(d^2 * 16/25)

(from: w = sqrt(d^2 * 4^2/(3^2+4^2)))
h = w * 3/4

Or in general, for a display with a width:height ratio of x:y, it is:
w = sqrt(d^2 * x^2/(y^2+x^2))

h = w * y/x

#### martyj19

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That's all very nice but it is much easier to measure the diagonal with a steel tape. And besides you have not accounted for the effect of 3:2 pulldown.

#### Albert C. Lee

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Quote:
 Originally Posted by KenV500 Use this link http://www.cavecreations.com/tv2.cgi
hehe, it's cool to see that people are still using that little app I wrote many moons ago. #### SteveTiilikainen

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Quote:
 Originally Posted by martyj19 That's all very nice but it is much easier to measure the diagonal with a steel tape. And besides you have not accounted for the effect of 3:2 pulldown.
Forgive the newbness, but how does 3:2 pulldown affect screen size? I thought it was just a trick for stretching 24 frames into 30 that had nothing to do with screen size.

#### DonoMan

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Quote:
 Originally Posted by SteveTiilikainen Forgive the newbness, but how does 3:2 pulldown affect screen size? I thought it was just a trick for stretching 24 frames into 30 that had nothing to do with screen size.
You are correct.

#### martyj19

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Quote:
 Originally Posted by SteveTiilikainen Forgive the newbness, but how does 3:2 pulldown affect screen size? I thought it was just a trick for stretching 24 frames into 30 that had nothing to do with screen size.
It's humor.

#### motomoto

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Quote:
 Originally Posted by Albert C. Lee hehe, it's cool to see that people are still using that little app I wrote many moons ago. that app is great! if you really wrote it, thanks #### BruZZi

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Quote:
 Originally Posted by Albert C. Lee hehe, it's cool to see that people are still using that little app I wrote many moons ago. Albert, I didn't know you were a AVS Forum Member. Thank you so much for the App.

That's Very Helpful.   .
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