Image sizes that actually matter
The pixel dimensions worth knowing for the web, social platforms and print — plus why "300 DPI" means nothing without a physical size.
Updated 2026-08-03
Most image-size advice is a list of numbers with no explanation, which is why it stops working the moment a platform changes something. The dimensions that survive are the ones derived from a constraint: an aspect ratio the layout enforces, a pixel density the display has, or a physical size the printer must fill. Here are those, with the arithmetic that generates them, so you can work out any number the list is missing.
Aspect ratio is the durable part
Platforms change their recommended pixel dimensions often; they change the shape of the frame almost never, because that would break every existing post. If you match the ratio, a crop never surprises you — and the exact pixel count only needs to be large enough.
| Ratio | Shape | Where it is used | A safe size |
|---|---|---|---|
| 1:1 | Square | Profile pictures, feed posts, avatars | 1080 × 1080 |
| 4:5 | Tall portrait | The tallest most feeds allow before cropping | 1080 × 1350 |
| 9:16 | Full-screen vertical | Stories, Reels, Shorts, TikTok | 1080 × 1920 |
| 16:9 | Widescreen | Video thumbnails, presentation slides, hero images | 1920 × 1080 |
| 1.91:1 | Wide landscape | Link previews (Open Graph, Twitter cards) | 1200 × 630 |
| 3:2 | Classic photo | What most cameras shoot; 6×4 inch prints | 1800 × 1200 |
DPI is not a property of your file
This is the single most persistent misunderstanding in image work. A digital image has pixels and nothing else. DPI — dots per inch — only becomes meaningful once you decide how large to print it, because it is the result of a division, not a stored quality. The DPI field in an image editor is a note about intended print size; changing it without resampling changes no pixels and no quality whatsoever.
- The formula is simply pixels ÷ inches = DPI.
- A 3000 × 2000 image printed at 10 × 6.7 inches is 300 DPI.
- The same file printed at 20 × 13.3 inches is 150 DPI.
- The same file printed on a billboard is about 3 DPI, and looks fine, because you are standing 50 meters away.
What you actually need for print
Required resolution falls as viewing distance rises, which is why a billboard needs fewer pixels per inch than a business card. 300 DPI is the standard for anything held in the hand and is genuinely overkill for anything else.
| Physical size | Pixels needed at 300 DPI | Acceptable at 150 DPI | |
|---|---|---|---|
| Business card | 3.5 × 2 in | 1050 × 600 | 525 × 300 |
| Postcard | 6 × 4 in | 1800 × 1200 | 900 × 600 |
| A4 page | 8.3 × 11.7 in | 2480 × 3508 | 1240 × 1754 |
| A3 poster | 11.7 × 16.5 in | 3508 × 4961 | 1754 × 2481 |
| A1 poster | 23.4 × 33.1 in | 7016 × 9933 | 3508 × 4967 |
| Roll-up banner | 33 × 79 in | Not required — 100 DPI is plenty | 3300 × 7900 at 100 DPI |
For the web, weight beats dimensions
On a web page nobody notices that your image is 1600px rather than 2400px wide. Everybody notices when the page takes four seconds to paint. Largest Contentful Paint — the Core Web Vitals metric that most often fails — is usually an image, and Google's "good" threshold is 2.5 seconds. The practical rule is to serve an image no more than twice the CSS pixel width it will occupy (enough for a high-density display, and no more), then compress it.
| Use | Sensible width | Target file size |
|---|---|---|
| Full-width hero | 1920px | under 200 KB |
| In-article image | 1200px | under 120 KB |
| Card or thumbnail | 600px | under 50 KB |
| Avatar | 256px | under 20 KB |
| Icon or logo | Use SVG | under 10 KB |
Never upscale to hit a number
If a printer asks for 300 DPI and your file is short, enlarging it in an image editor does not add detail — it invents pixels by interpolating between the ones you have, producing a softer image at a bigger number. The honest options are to print smaller, reshoot, or accept a lower DPI at a viewing distance where it does not matter. A genuinely sharp 150 DPI print beats an upscaled 300 DPI one every time.
Questions
What size should my image be for a website?
No wider than twice the space it occupies on screen. A photo displayed 600 CSS pixels wide should be about 1200px, which covers high-density displays with nothing wasted. Then compress it — WEBP at quality 75–80 typically lands well under 120 KB at that width and is visually indistinguishable from the original.
Is 300 DPI always required for printing?
No. 300 DPI is the convention for anything viewed at reading distance — cards, flyers, photo books, magazines. Posters seen from two meters are fine at 150, and large-format banners are routinely produced at 100 or less. Required resolution falls as viewing distance rises.
How do I change an image from 72 DPI to 300 DPI?
For a digital file, there is nothing to change: the pixels are the same either way. What matters is pixels ÷ intended print size. If a printer insists on the tag, set it without resampling — the file is unaltered. If the pixel count is genuinely too low for the size you want, the only real fixes are printing smaller or starting from a higher-resolution original.
Why does my image get cropped on social platforms?
Because its aspect ratio does not match the frame, so the platform cuts the excess — usually from the top and bottom. Match the ratio first and the pixel dimensions second. If the same image has to work in more than one frame, keep the subject inside the center square, which every ratio contains.