Screens are often measured diagonally. There are people expecting width and height to be the main numbers. But the diagonal number keeps showing up, even on modern displays.
The start of diagonal screen measurement
In one online discussion, it was pointed out that this practice is older than flat screens. Long before LCD or OLED panels existed, CRT televisions were already measured diagonally.
Those older TVs used tubes, and the visible screen area was curved and not perfectly rectangular. It was less clear to measure width or height, but the diagonal gave a single number that worked across different shapes.
This explanation is commonly mentioned, although exact historical standards may vary by manufacturer.
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Using one number instead of width and height
Another frequent explanation in the discussion is simplicity. A diagonal measurement gives one number instead of two. Many buyers want a quick idea of size without doing calculations.
If most screens follow the same aspect ratio, like 16:9, the diagonal often gives a reasonable sense of how big the screen will feel. It works as a rough guide though it does not mean it tells you everything.
Marketing and perceived size
The discussion also mentions marketing as a possible factor. A diagonal is usually the largest possible measurement of a rectangle. A larger number can sound more impressive, even if the actual screen area is not much different.
This idea comes up often in discussions, but it is usually framed as a practical business choice rather than a technical one.
Diagonal number gives easier way to compare size
Screens come in different shapes, not just one standard form. Because of this, width and height can be misleading on their own if no aspect ratio mentioned.
Two displays might share a similar width OR height but still look very different in overall size.
The diagonal number avoids this by giving a single value that works across different aspect ratios. It does not describe the exact shape or guarantee physical fit, but it gives a rough and easy way to compare screen size without needing extra calculations.
The problem with diagonal size and physical fit
An important limitation is also noted in the discussion. Diagonal size does not help much when you need to know if a screen will physically fit in a space. Bezels, stands, and overall frame design vary between models.
Even two TVs with the same diagonal can have different total widths and heights. That is why product specification sheets still list exact dimensions.
The diagonal number is more like a category label than a practical installation guide.
Overall, measuring screens diagonally is because it is familiar, simple, and widely understood, though not the most precise. It works well enough for quick comparisons, but it often needs extra information to be truly useful.