How big of a widescreen do I need to match the height of my current 36" 4:3 TV?

January 16, 2009 2:21 PM

I have a 36" standard 4:3 aspect ratio tube-type TV. I'm very happy with the vertical size of the tube and when I buy a new HDTV with a 16:9 ratio, I'd like to end up at that same vertical size.

Of course, TVs aren't marketed by the width and height of their screens, but by measuring across the diagonal, to make them seem so much bigger than they really are. I don't know the height of my current screen offhand, but I'm certain that, knowing the diagonal measurement of my current TV, one more skilled in geometry would be able to arrive at the proper diagonal screen size of the new widescreen model to retain that same vertical height.

Wouldn't one?

posted by DandyRandy to technology (14 comments total)

You may find this link to be useful. I did while I was shopping for a TV. TV Aspect Ratio Converter
posted by raygan at 2:29 PM on January 16 [1 favorite]

You want the Pythagorean theorum here. A^2 + B^2 = C^2. The diagonal length = C. Of course, don't forget that there's going to be a frame around the screen, if you're trying to fit the new TV onto a vertical-height limited shelf.
posted by amelioration at 2:31 PM on January 16

According to raygan's link, you'd want a 44" screen.
posted by katieinshoes at 2:32 PM on January 16

Of course 44" tvs don't exist to my knowledge; you should probably look for a 40" or a 50".
posted by raygan at 2:35 PM on January 16

42" and 46" screens are also widely available.
posted by indyz at 2:38 PM on January 16

From the Pythagorean Theorem:

a² + b² = c²

The 4:3 aspect ratio helps, because we then know the diagonal is 5 in these units:

3*3 + 4*4 = 9 + 16 = 25 = 5*5

We can take our special 3:4:5 triangle and set up this equation:

(3x)^2 + (4x)^2 = (5x)^2

We know our diagonal is 36 inches long:

5x = 36 inches

Therefore:

x = 7.2 inches

The vertical height is therefore:

3x = 21.6 inches
posted by Blazecock Pileon at 2:39 PM on January 16

The ratio of 4:3 to 16:9 is 4:3, so to get the same height, you want a TV that is 4:3 times as wide as your 4:3 TV!

4:3 is convenient to do math on, since it's two 3,4,5 right triangles. So a 36" TV is 28.8 x 21.6

Multiply 28.8 by 4/3 and you get 34.4". 34.4 x 21.6 is ... (busts out a calculator) a 40.6" diagonal.

Get something close to that.
posted by aubilenon at 2:43 PM on January 16

Pythagoras be dammed, your 36" includes 2" you can't see around the tube.

You want a 42" or a 46".
posted by bensherman at 2:44 PM on January 16

IIRC, tubes in the US had to be measured from edge-of-bezel to edge-of-bezel, which is why screen sizes for the same model were smaller in the US than elsewhere. Of course, I may have the directionality there reversed, and it might have been the US that measured raw tube size and somewhere else that measured bezel-to-bezel.

I would bet that you find a 42" a wee smidge smaller vertically than your current set, and a 46 a bit bigger.
posted by ROU_Xenophobe at 3:05 PM on January 16

CRT TV sizes in the US are measured bezel-to-bezel. It's computer CRT screens that are given as the size of the tube.
posted by zsazsa at 3:25 PM on January 16

Why not simply use a tape measure to find out how tall your actual tube is, and then compare it when you go shopping for a new widescreen?

It's simple, but it should work. If that's not your choice, the geometry has been well explained.
posted by jellywerker at 6:09 PM on January 16 [1 favorite]

At least 44 inches. I love Google calculator.
posted by w0mbat at 1:40 AM on January 17

A consideration is that anything that you are seeing letterboxed now is going to be taller vertically on a 16:9 screen, even if the vertical is the same, because you'll get rid of the black bars.
posted by smackfu at 6:00 AM on January 17

The tape measure solution came to mind, of course, but I was more interested in working it out geometrically.

Many thanks for the great answers!
posted by DandyRandy at 11:21 AM on January 17