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

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?

Relevance

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.

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.