Image Aspect Ratios: Work Them Out and Choose One
By Akmal Ali · Published · Updated · 4 min read
Work out a ratio by dividing the width and height by their greatest common divisor, then match it to where the image will go: 3:2 for 6 × 4 prints and most cameras, 4:5 or 9:16 for social posts and Stories, 16:9 for video and slides. When the shapes differ, crop to the new ratio first, because resizing alone would stretch the picture.
A photo that looked fine on your phone comes back from the print shop with the top of someone’s head missing. A video uploaded as a Story sits in a thin strip with black bars above and below. Both are aspect-ratio problems: the shape of the image didn’t match the shape of where it went.
Which ratio goes where?
| Ratio | Width ÷ height | Example sizes | Typical uses |
|---|---|---|---|
| 1:1 | 1.00 | 1080 × 1080 | Square posts, profile pictures, product thumbnails |
| 4:5 | 0.80 | 1080 × 1350 | Portrait posts in social feeds |
| 4:3 | 1.33 | 4000 × 3000 | Most phone photos, tablets, older slides |
| 3:2 | 1.50 | 6000 × 4000 | DSLR and mirrorless cameras, 6 × 4 inch prints |
| 16:9 | 1.78 | 1920 × 1080 | HD and 4K video, TVs, most monitors, slides |
| 9:16 | 0.56 | 1080 × 1920 | Stories, Reels, Shorts and other full-screen vertical video |
| 1.91:1 | 1.91 | 1200 × 630 | Link previews when a page is shared |
Platforms change their recommended sizes from time to time, so check their help pages before a campaign. The shapes change far less often than the pixel counts.
Working out the ratio of an image
Divide the width and the height by their greatest common divisor, the largest number that divides both: 4000 × 3000 divides by 1000 to give 4:3. If you don’t want to find it, divide the width by the height and compare the decimal with the table above. Some sizes don’t reduce neatly: a 1366 × 768 laptop screen is 683:384, or 1.78, so it is called “about 16:9”, and a 2560 × 1080 “21:9” monitor is really 64:27.
Aspect Ratio Calculator
Find the ratio of any size, or the missing width or height for a new size, with presets for 1:1, 4:3, 3:2, 16:9 and 9:16.
Prints: where the crop comes from
Print sizes have their own shapes, and a print lab fills the paper by cutting off whatever doesn’t fit. Here is how much of a 6000 × 4000 camera photo (3:2) each common print loses if the full height is kept:
| Ratio | Width that fits | Cut from the width | |
|---|---|---|---|
| 6 × 4 in | 3:2 (1.5) | 6000 px | Nothing |
| A4 or A3 | 1.41 | 5657 px | 343 px, about 6% |
| 7 × 5 in | 1.4 | 5600 px | 400 px, about 7% |
| 10 × 8 in | 5:4 (1.25) | 5000 px | 1000 px, about 17% |
Phone photos go the other way. A 4:3 photo is taller than a 6 × 4 print, so about 11% of its height is cut. In every case, crop the photo yourself to the print’s ratio before ordering, with the image cropper, so you decide what goes. For the pixels a print needs, see how to check image DPI and PPI.
Video and social posts
Standard video is 16:9; vertical video is the same shape turned on its side, 9:16. A 16:9 clip in a 9:16 slot keeps only a narrow strip, with bars above and below, so reframe or crop it instead. In feeds, a 4:5 portrait post takes up more of the screen than a square or landscape one, which is why it is popular for photos.
What happens when you change the ratio?
Resizing keeps the ratio. To turn a 4:3 photo into a 1:1 square, part of it has to go, so crop first and then resize. Forcing a 4:3 image into square dimensions squeezes everything sideways. The other option is to keep the whole image and add bars or a background around it, which is common for video and product photos. When you resize within the same ratio, scale both sides by the same factor: 1200 wide for a 4000 × 3000 photo means 1200 × 3000 ÷ 4000 = 900 high. The image resizer keeps that locked for you.
On a web page
Tell the browser the shape of each image so the page doesn’t jump while it loads. Give every <img> its width and height, or reserve the space with CSS:
.hero img {
width: 100%;
height: auto;
aspect-ratio: 16 / 9;
object-fit: cover;
}To find the real pixel size of a photo first, open it in the image dimensions checker, which shows the ratio and the nearest common one.
Frequently Asked Questions
What aspect ratio is A4 paper?
1:√2, about 1:1.414. Every ISO A size has the same shape, so a design made for A4 scales to A3 or A5 without cropping.
Why is my phone photo cropped on a 6 × 4 print?
Most phone photos are 4:3, which is taller than the 3:2 shape of a 6 × 4 print, so the lab trims about 11% of the height. Crop it to 3:2 yourself first to choose which part goes.
Should slides be 16:9 or 16:10?
Use 16:9 unless you know the screen: most projectors, TVs and monitors are 16:9, and PowerPoint and Google Slides start new presentations in it. A 16:9 slide on a 16:10 laptop screen just shows thin bars above and below.