1. Measuring Systems
One pica or two?

2. Only the United States, Liberia, and Myanmar use Imperial units.
Before we move on, I just wanted to point out how archaic it is to use inches.
Only the United States, Liberia, and Myanmar use Imperial units.
However, many more countries use the U.S. standard letter size, which is in imperial units.

3. Numbers Graphic Designers Work With
Inches
Picas
Pixels
Points
Ratios
Resolution
On that note, designers have to use inches. And picas, pixels, points, ratios, resolution.

4. Paper Sizes Imperial Metric Letter: 8.5x11 in Tabloid: 11x17 in
ANSI C: 17x22 in
A4: 210x297 mm (8.27x11.7 in)
A3: 297x420 mm (11.7x16.5 in)
A2: 420x594 mm (16.5x23.4 in)
You’ll see inches used most with paper sizes and some graphic sizes. Here are a few of the most common.

5. What’s the Best Paper Size?
If you haven’t watched this video yet, watch it. You’ll realize that A4 is better. But more importantly, you’ll see how ratios are used and why they matter.

6. 1 in = 6 p = 72 pts
In the old days they broke the inch down into 6 picas, and they broke the pica down into 12 points.
So, at 12 points per pica, 6 picas per inch, 12 times 6 is 72, we get 72 points per inch.
In other words, a 72 point font is 1 inch tall

7. Pixels & Resolution
When screens came around, they were made up not of points of ink, but points of light.

8. Resolution is how many pixels there are.
Screens are getting more and more pixels in there, making them higher and higher resolution.

9. Common Screen Resolutions
480 x 320 : VHS Videotape
720 x 576 : SD (DVD)
1280 x 720 : 720 HD (Blu-ray)
1920 x 1080 : 1080 HD (Blu-ray)
3840 x 2160 : 4K TV
320 x 480 : original iPhone
750 x 1334 : iPhone 6
2048 x 1536 : iPad Air 2
Common Screen Resolutions
You don’t have to memorize these, but you will occasionally have to look them up when you’re designing something to be used on a particular screen.

10. Ratios
1:1 (Instagram) 1.33:1 or 4:3 (old TV) 1.375:1 (standard film) 1.41:1 (A4 paper, etc.) 1.618:1 (golden ratio) 1.77:1 or 16:9 (HD) 1.85:1 (U.S. widescreen)