Are the inches measured by a tape measure different than inches measured by pixel count?

Question

So I was looking at the size of my monitor. 14 inches according to every box and label. I got out my tape measure and the tape measure says it's about 15.5 inches. So I calculated the number of pixels (~2074 in the native resolution of the monitor) and converted that number to inches and it came out right at 14 inches.

Did I miscalculate something or is there some weird difference in inch measurements?

Perhaps it's something to do with the resolution of the monitor?

Answer 1

TV or computer monitors label their size by the diagonal. The 14 inches is actually the length of the diagonal not the vertical or the horizontal length.

Answer 2

If it's a CRT monitor, all bets are off. However, if it's an LCD monitor like yours, you can do some simple calculations.

When a monitor reports its size, it's reporting the length of the diagonal (to get a bigger, more impressive number). So, a 17-inch monitor with a resolution of 1280x1024 has an aspect ratio of 5:4 (you know this from the native resolution), and a diagonal of 17 inches. After doing some math:

x^2 + y^2 = 17^2
x/y = 5/4

solve these simultaneous equations for x and y to find
x = 13.27 inches
y = 10.62 inches

So, the number of pixels per inch is:
1280 / 13.27 = 96.42 pix/inch

If you also measure the actual horizontal and vertical dimensions with a ruler and find them to be different, the only explanation is that your pixels aren't square, but are instead squashed in some way.

Or, alternatively, you are using a faulty pixels-per-inch conversion factor. It's better to calculate this number based on the number of pixels and the physical measurement than to assume it in the first place.

Answer 3

Inches are inches, anyway you describe them. They don't change.