What is DPI and does it actually matter for web images?

DPI stands for dots per inch and originates from print technology, where it describes how many ink dots a printer places per inch of paper. PPI stands for pixels per inch and describes the pixel density of a digital display. In everyday image editing and file conversations, the two terms are often used interchangeably, even though they technically refer to different things.

When people talk about the DPI setting in an image file, they are referring to metadata embedded in the file that suggests how large the image should be printed. An image tagged as 72 DPI and an image tagged as 300 DPI can have exactly the same number of pixels. The DPI label does not change the pixel count, the file size, or how the image looks on a screen.

This is the core confusion that trips up many people. DPI in a file is a recommendation for print size, not a description of digital quality. Changing the DPI tag in a file without resampling it does not add or remove any pixels, and it does not change how the image looks on screen.

Web browsers ignore the DPI metadata embedded in image files. When a browser displays an image, it simply uses the pixel dimensions — the number of pixels wide and tall the image contains — and maps them to screen pixels. A 1200 by 800 pixel image displays at 1200 by 800 pixels in the browser, whether the file is tagged as 72 DPI, 96 DPI, or 300 DPI.

This means that if you open an image in Photoshop or another editor and change the DPI setting from 72 to 300 without resampling, the browser will display the image at exactly the same size and quality as before. Nothing has changed except the metadata label.

File size is also not affected by the DPI tag itself. A file tagged as 300 DPI is not larger than an identical file tagged as 72 DPI. What affects file size is the number of pixels (pixel dimensions) and the compression applied, not the DPI label.

DPI matters for print. When you send an image to a printer, the printer uses the DPI setting (or a default if none is set) to determine how large to print the image and how many dots to use per inch of output. An image with 3000 pixels wide printed at 300 DPI will print 10 inches wide. The same image printed at 150 DPI will print 20 inches wide at lower detail per inch.

The practical implication for print is that more pixels at the intended print size means sharper print output. A standard rule of thumb is 300 DPI at the intended print size for high-quality print. A 1200 pixel wide image can print at high quality at 4 inches wide (1200 ÷ 300 = 4 inches). Printing the same 1200 pixel image at 10 inches wide results in only 120 DPI, which looks soft or pixelated on paper.

DPI also matters for PDF files that will be printed rather than read on screen. PDFs created for print should embed images at 300 DPI or higher at their intended print dimensions. PDFs created for screen-only distribution — portal submissions, email attachments, shared reports — do not require 300 DPI and will be significantly smaller at 150 DPI without any loss in screen readability.

The confusion usually arises when someone exports an image at 72 DPI for web and then is told it needs to be 300 DPI. The instinctive response is to change the DPI setting in the software. But if the pixel dimensions stay the same, nothing about the image quality has changed — only the metadata label.

What the person asking for 300 DPI usually actually means is that they need a larger image — more pixels — so it prints well at the size they have in mind. The right fix is to re-export the image at higher pixel dimensions from the source, not to relabel a small image as 300 DPI.

If you receive feedback that an image needs to be 300 DPI, ask what the print size is. Then calculate how many pixels you actually need (print width in inches multiplied by 300) and provide an image with at least that many pixels. That is the correct way to meet a print DPI requirement.

For web use, the DPI setting is irrelevant. Focus on pixel dimensions (width and height in pixels) and file size. Set the pixel dimensions to the maximum size the image will be displayed at, compress to a practical quality level, and save in the right format. The DPI label in the export settings does not affect the result.

For print use, focus on pixel dimensions at the intended print size. If you need a 6-inch wide print at 300 DPI, you need at least 1800 pixels wide (6 × 300). For professional print work, 300 DPI at the intended output size is the standard. For large-format prints viewed from a distance, 150 DPI or even 100 DPI at the print size is often sufficient.

For PDF files, set the image resolution at 150 DPI for screen-only documents and portal submissions. Set it at 300 DPI for PDF files that will be printed professionally. The difference in file size between these settings is substantial.

• Web images: DPI is irrelevant. Focus on pixel dimensions and compression.
• Print images: use 300 DPI at the intended print size as the standard.
• PDF for screen: 150 DPI embedded images are sufficient and produce smaller files.
• PDF for print: 300 DPI embedded images for professional quality.
• Large-format print viewed from a distance: 100 to 150 DPI at print size is often sufficient.

If a client or colleague asks for "a 300 DPI image" for a website, the most helpful response is to clarify whether they mean they need it for print or for screen. For screen use, a 300 DPI label adds no value. For print, they need a specific pixel dimension based on the print size they have in mind.

If you are uploading images to a web platform and the form says images must be 72 DPI, that requirement is technically meaningless for display quality. What they probably mean is that they do not want massive print-resolution images uploaded. You can satisfy this requirement by exporting at 72 DPI metadata label, but the actual display quality is determined entirely by pixel dimensions and compression, not the DPI tag.