"But it looks fine on my screen." We hear this from clients a lot and there is a good reason for it.
Screen resolution is measured in pixels per inch (PPI). A pixel is a tiny square of color. Computer monitors (as well as most screens) use the tiny pixels to assemble text and images on screen. The optimal resolution for screens is 72 PPI. Increasing this resolution does not make the image look any better, it only makes a file larger.
But print resolution is typically measured in dots per inch (DPI), and it refers to the number of dots (or pixels) that a printer can place within a one-inch space. The more dots per inch, the finer the detail will be. This measurement is important when preparing images and artwork for print, as it directly affects the quality and clarity of the printed output.
Standard minimum print resolution for high-quality printed materials is 300 DPI. This means there are 300 dots of ink or toner per linear inch. If the resolution of your photo or artwork is too low, there won't be enough detail to produce a sharp print. Check the resolution of your image in pixels, and then ensure it meets the recommended resolution for printing.
How to Check Your Resolution in 2 Easy Steps
On a Mac
Right-click (or control-click) on an image.
Select “Get Info.”
Under the “More info” tab, look for Dimensions.
You should see a number like “1024 x 768” (some number x some number).
These numbers show the number of pixels in the image (width x height)
On a PC
Right-click on image icon.
Select “Properties.”
Click the “Summary” tab in the properties window.
You’ll see values for the Width, Height, Horizontal Resolution and Vertical Resolution.
Calculate the DPI
So, if you have an image that is 1024 × 768 (listed as Width=1024px, Height=768px on a PC), you simply divide each value by 300 to see how many inches you can print at 300 dpi.
1024 ÷ 300 = 3.4133″ (width), 768 ÷ 300 = 2.56″ (height)
So, you could print this 1024px × 768px image at 300 DPI at a mechanical size of 3.4133″ × 2.56″ – any bigger than this, and you risk the image turning out blurry or "pixellated."