If you’ve ever worked with photoshop, chances are you’ve run into this issue: You want to view your image at the exact size that it will print, so logically, you go to View > Print Size and notice that it’s no where near the size it should be. If you’re like most designers, you just accept this as a flaw in Photoshop and work around it. But to hell with that, why is the feature even there if it doesn’t work? Well, the short answer to that question is that it does work.
So, why does Print Size on the screen not equal Print Size on paper?
Simply put, Photoshop doesn’t know the size of your screen. Every screen has a different pixel density that we measure in pixels per inch (ppi). This number is determined by 2 things:
- The size of your monitors viewable area
- The resolution you have your monitor set to.
By default, pixel density in Photoshop is set to 72ppi. This number was determined sometime in the 80’s by the graphic design fairies to be the magical number that all screen documents are set to. From then on, it was drilled into the heads of graphic designers all around the world: When you are creating something that will be viewed on a screen — 72 is the pixels per inch that you better set your document to; otherwise, sh!t gets weird. And it was never questioned again… until today.
How can we fix pixel density in Photoshop?
First we need to calculate diagonal resolution of your screen. We do this with an old friend from high-school, and he hasn’t aged well: The Pythagorean Theorem! I can hear all of your cheers for joy from here.
Add the square of the width of your screen in pixels to the square of the height of your screen in pixels and then take the square root of the whole sickeningly nostalgic mess and bang: The Diagonal Resolution is yours (and you can frolic happily down the yellow brick road with the scarecrow). Aced that one. If your running the same resolution as me (1920 x 1200), then you should get 2264.1555 pixels.
Now that we have that, it’s time to calculate pixel density.
This one is way easier: All you have to do is take your diagonal resolution and divide it by the diagonal size (in inches) of your monitors viewable area. In my case: 2264.1555 px diagonal resolution divided by my monitor’s 24″ screen and the result is 94.339 ppi.
Easy right? Don’t want to do the work, eh? Alright, there is a calculator that will do all that math for you. Sorry, I really should have started with that link. There I bolded it for you, happy?.
Now that we have our screen’s pixel density, we can plug it into Photoshop. Open preferences and select Units & Rulers. Plug the screen density into the Screen Resolution field under New Document Preset Resolutions.
Now, check your document with View > Print Size and… 1 inch = 1 inch!
Quick Google search on the “72 ppi myth” and you’ll get pages of people explaining why this is (and sadly most don’t know the difference between ppi and dpi). Let me fix this in ONE LINE:
PPI DOES NOT EQUAL DPI
They are different terms; please, stop using them interchangeably. Pixels are what you screen is made of, and Dots are what printers spit out of their printer heads.
But why 72? What’s so special about that number? Well, like I said: In the 80’s, designers started standing up from their tracing tables, putting down their pen-knives, and emerging from a rubber-cement-fueled state of inebriation. What they saw then was a strange glowing box that could help them design things faster and easier than ever before. This magical box (that we will call Mac) said onto them:
The size of a Point (the unit for measuring type) should correlate on a 1 to 1 ratio with that of a pixel. There are 72 Points to an inch; therefore, there must be 72 pixels to an inch as well.
The designers, now focused more on the glow of the box and the prospect of never having to smell rubber cement again, completely disregarded (and subsequently accepted) the fact that 72 was the magic number and anyone questioning this number should be rubber-cemented and feathered.
Today, our glowing boxes are considerable more powerful and boast twice as much glow. So let it be known, 72ppi is dead people — let’s move on. Calibrate your design software to the size and resolution of your screen, and the pain of losing that comfy little number we all knew and loved will surly fade.