DPI and PPI get used interchangeably so often that most people assume they’re the same thing. They’re not. PPI (pixels per inch) describes a digital image on a screen. DPI (dots per inch) describes a physical print. Here’s what each one actually measures, why “72 DPI for web” is a myth, and what really controls your file size and quality.
PPI: Pixels Per Inch (Screens and Digital Images)
PPI describes how densely pixels are packed into an inch of a digital image or display. A photo that is 3000 × 2000 pixels contains a fixed number of pixels — 6 million of them — no matter what device displays it. PPI only becomes meaningful when you talk about a specific physical size: that same image is 10 inches wide at 300 PPI, or 41.6 inches wide at 72 PPI.
A digital image file doesn’t have an inherent size in inches. It has pixel dimensions. PPI is just a label describing how those pixels would map to inches if printed or displayed at a particular density. Change the PPI number without resampling, and the pixel count — and file size — barely change at all.
DPI: Dots Per Inch (Physical Printing)
DPI describes something physical: how many ink or toner dots a printer lays down per inch of paper. This is a property of the printer, not the image file. Because printers build up color and shading using multiple overlapping dots per pixel (halftoning), DPI and PPI aren’t even a 1:1 mapping — a printer might use 4+ physical dots to render one image pixel’s color information.
Why the Two Terms Get Confused
Photoshop’s image size dialog has long labeled its pixel-density field “Resolution” in units of pixels/inch, but the broader industry has used “DPI” as a catch-all term for both concepts for so long that it stuck. The practical fix: for a screen or digital file, think PPI. For a physical printer, think DPI. Only the second one involves actual ink dots.
The “72 DPI for Web” Myth
- Browsers don’t read or care about an image’s embedded DPI/PPI metadata at all — they render based purely on pixel dimensions relative to CSS display size
- The “72 DPI” number traces back to 1980s Mac displays and has had no technical relevance to modern screens (90–500+ PPI) for decades
- A 3000×2000 image tagged “72 DPI” and the same image tagged “300 DPI” render identically in every browser — the metadata is ignored
What actually matters for web images is pixel dimensions, not any DPI/PPI tag. If an image needs to display at 800 pixels wide, export it at 800 pixels wide (or 1600 for crisp rendering on high-density screens).
How Resolution Actually Relates to File Size
| Factor | Effect on file size |
|---|---|
| Pixel dimensions (width × height) | Directly proportional — more pixels = more data |
| Compression format (JPEG, PNG, WebP) | Large — JPEG/WebP discard redundant data, PNG doesn’t |
| Compression quality setting | Large — lower quality = smaller file, same pixel count |
| Color depth (8-bit vs 16-bit) | Moderate — more bits per pixel = larger file |
| DPI/PPI metadata tag | None — this is just a label, not image data |
If you change “Resolution” from 72 to 300 in an editor without resampling, file size barely moves — you’ve only edited a metadata tag. Relabeling DPI never improves print quality either: the pixel data is identical, it just claims to print smaller.
What DPI Should You Actually Use?
| Use case | Recommended |
|---|---|
| Standard document/photo printing | 300 DPI |
| Large-format prints (posters, banners) | 150 DPI |
| Fine art / professional photo prints | 300–600 DPI |
| Website images, social media, email | Pixel dimensions matter, not DPI |
| Screens (phones, monitors, TVs) | PPI is a hardware spec, not something you set |
Rule of thumb for print: multiply your target physical size by your target DPI to get required pixel dimensions (8×10 inches at 300 DPI = 2400×3000 pixels). If your source doesn’t have enough pixels, no DPI relabeling fixes that.
How to Check an Image’s DPI/PPI
- Windows: Right-click the file → Properties → Details tab → “Horizontal/Vertical resolution” under Image
- Mac: Open in Preview → ⌘I to show the inspector → General tab shows resolution alongside pixel dimensions
- Online tools: Most display pixel dimensions immediately on upload — the number that actually matters for web use
Getting Your Image to the Right Pixel Dimensions
Since pixel dimensions actually control quality and file size, the practical next step is getting your image to the correct pixel size for its destination, then compressing it efficiently. AllMediaTools doesn’t edit DPI metadata directly — no pixel-based web image tool needs to — but once you know your target pixel dimensions:
- Resize an image to the right pixel dimensions for your use case.
- Run it through AllMediaTools Image Compressor to shrink file size without visible quality loss — see our guide on compressing images without losing quality.
Frequently Asked Questions
What DPI should I use for printing?
300 DPI is standard for most document and photo printing at normal viewing distance. Large-format prints like posters and banners can use 150 DPI or lower without a visible quality drop, since they’re viewed from further away.
Does changing DPI change file size?
Only if the change also resamples the image (adds or removes actual pixels). Editing just the DPI/PPI metadata tag, without resampling, leaves pixel data untouched and barely affects file size.
What PPI is good for a website?
PPI/DPI metadata is irrelevant for websites — browsers ignore it and render based on pixel dimensions alone. Export at the pixel width the image will actually display at, and roughly double that for crisp rendering on high-density “Retina” screens.
How do I check an image’s DPI?
On Windows, right-click the file → Properties → Details → Image section. On Mac, open it in Preview and press ⌘I. Most online image tools show pixel dimensions immediately, which is the more useful number for anything screen-related.