What it means
A digital picture is made of a grid of pixels. How sharp it looks depends on how many pixels are packed into each inch of the screen or page.
Stretch the same pixels over a bigger area and the picture becomes fuzzy, because each pixel is larger. Screens and print have different needs.
Phone screens often have a high pixel density, so text looks crisp, while many printers need images of around 300 pixels per inch for photograph-quality results. Large banners seen from a distance can use much lower values.
The calculation helps teams avoid costly mistakes. A logo that looks fine on a website may look blurry when printed on an annual report cover, because it contains too few pixels for the printed size.
Checking the pixel dimensions before sending files to a printer avoids reprinting. PPI is often confused with DPI, or dots per inch.
PPI refers to the pixels in a digital image or screen, while DPI describes how many ink dots a printer lays down. People use the two terms interchangeably in everyday talk, but the first belongs to the file and the second to the printer.
For finance and marketing teams, the practical points are file quality and cost. High-resolution files are larger, take longer to send and may cost more to store, so the aim is to match resolution to the use.
A dashboard for a boardroom screen and a printed investor report need different settings. The acronym appears elsewhere in finance, where PPI usually means the producer price index.
Always check the context before assuming which one a speaker means. Teams that print often should also keep a master copy of each logo in a vector format, which can be scaled to any size without losing sharpness.
In practice
Real-world examples.
Example
A marketing team prepares a 6-inch-wide product photo for a brochure. At 300 PPI the image must be at least 1,800 pixels wide, so the designer rejects a 900-pixel file from a website. She asks the photographer for the original file instead.
Example
A finance team exports charts for a board pack to be viewed on large screens. They choose a moderate PPI to keep file sizes small while keeping the numbers readable. The pack opens quickly on every laptop in the room.
Example
A trade show stand uses a banner that is 8 feet wide and seen from several metres away. The printer advises that 50 PPI is enough, which saves money on file size and printing time. A heavier file would have cost more to send and print without any visible gain.
Formula
Calculation
PPI = Number of pixels along one side / Length of that side in inches
Required pixels = Print size in inches x Target PPI
A design team wants to print a chart image 10 inches wide in an annual report at 300 PPI.
Required pixels = 10 x 300 = 3,000 pixels wide.
If the image supplied is only 1,500 pixels wide, printing it at 10 inches gives PPI = 1,500 / 10 = 150, which is half the target and will look noticeably soft.Case study
Seen in the real world.
Orchard Capital Advisers is a fictional wealth manager that printed 2,000 glossy annual reviews for clients. The designer had used images copied from the firm's website, which were only 800 pixels wide, and the covers came back looking blurred.
The reprint cost $6,500 and delayed the mailing by two weeks. In this illustrative case, the firm introduced a short checklist that asked designers to confirm pixel dimensions against the printed size before approving files, and it has not had a similar problem since. The checklist also lists the printer's required file format, bleed margin and colour profile. The extra five minutes of checking is now built into the approval step for every client document. The cost of the checklist is negligible compared with the cost of a single reprint, and clients noticed the sharper covers straight away.
Watch out
Common mistakes.
- Using a website image at print size without checking its pixel dimensions.
- Increasing the PPI setting in software without adding real detail, which does not make a blurry image sharper, since the software can only invent pixels and cannot recover lost detail.
- Mixing up PPI with DPI, which describe the image and the printer respectively.
Questions
People also ask.
What PPI is needed for printing?
Around 300 PPI is a common target for high-quality print, while large display graphics can use much less.
What is the difference between PPI and resolution?
Resolution is the total pixel dimensions of an image, such as 3,000 by 2,000, while PPI links those pixels to a physical size.
Does a higher PPI always give better results?
Not always, because beyond a certain point the eye cannot tell the difference, and the larger files only slow things down, which adds cost for storage and sending.
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