An aspect ratio is the shape of a picture: its width divided by its height. To crop to a ratio, you cut the largest rectangle of that shape out of the photo and throw the rest away, and the picture is never stretched. In an image cropper you pick the ratio, drag the box over the part you want to keep, and save. This article explains what the ratios 1:1, 4:3, 16:9, 3:2 and 9:16 mean, shows exactly how many pixels each one leaves from a real-sized photo, and covers rotating, flipping and keeping the quality.
What an aspect ratio is
A ratio says how much wider than tall a picture is, not how big it is. A picture of 1920 by 1080 pixels and one of 3840 by 2160 pixels have the same ratio, 16:9, because both reduce to the same fraction: 1920 ÷ 1080 = 1.7778, and so does 3840 ÷ 2160. To reduce a size to a ratio, divide both sides by their greatest common divisor: 1920 and 1080 share 120, which leaves 16 and 9.
The ratio is also what makes a crop look "right" when a place needs a particular shape. A square profile picture wants 1:1. A video thumbnail wants 16:9. Put a photo of the wrong shape there and the site either crops it for you, in the middle and without asking, or adds empty bars. Cropping yourself lets you choose what is kept.
Platforms change their recommended pixel sizes from time to time, so this article talks about ratios, which stay put, not about the exact size of any one site. Check the current guidance of the place you upload to if it asks for a specific pixel size, then crop to its ratio and resize afterwards.
The common ratios and what they suit
| Ratio | Shape | Often used for |
|---|---|---|
| 1:1 | Square | Profile pictures, square posts, app icons |
| 4:3 | Slightly wider than tall | Classic photos, slides, many tablets |
| 16:9 | Widescreen | Video, thumbnails, wide backgrounds |
| 3:2 | A little wider than 4:3 | Photos from most cameras, 6 by 4 inch prints |
| 9:16 | Tall and narrow | Vertical stories and short videos |
Ratios not in the list, such as 4:5 or 21:9, still work: use the width and height fields described below.
What each crop leaves: worked numbers
Take a photo of 4000 by 3000 pixels, which is 4:3. The largest centred crop for each ratio is:
| Ratio | Crop size | Left edge | Top edge | Share of the photo kept |
|---|---|---|---|---|
| 1:1 | 3000 × 3000 | 500 | 0 | 75% |
| 4:3 | 4000 × 3000 | 0 | 0 | 100% |
| 16:9 | 4000 × 2250 | 0 | 375 | 75% |
| 3:2 | 4000 × 2667 | 0 | 167 | 89% |
| 9:16 | 1688 × 3000 | 1156 | 0 | 42% |
The tool rounds to whole pixels, so 4000 ÷ 1.5 = 2666.67 becomes 2667. The 9:16 row shows why a tall crop from a landscape photo is so costly: you keep a narrow strip, 1688 pixels wide, and lose almost 60% of the picture.
The same ratios from a portrait photo of 3024 by 4032 pixels (3:4):
| Ratio | Crop size | Left edge | Top edge |
|---|---|---|---|
| 1:1 | 3024 × 3024 | 0 | 504 |
| 4:3 | 3024 × 2268 | 0 | 882 |
| 16:9 | 3024 × 1701 | 0 | 1166 |
| 3:2 | 3024 × 2016 | 0 | 1008 |
| 9:16 | 2268 × 4032 | 378 | 0 |
The rule behind all of these: for a ratio r, the crop height is the crop width divided by r. The widest crop uses the full width, unless the height then runs past the photo, in which case the full height is used and the width is height times r. A different example: a 3:2 camera photo of 6000 by 4000 pixels printed at 8 by 10 inches needs a 4:5 shape. The tallest 4:5 crop is 3200 by 4000, so 2800 of the 6000 columns are discarded. Better to know that before you press print than after.
Cropping step by step
- Open the image crop tool. Drop the picture on the box, choose it, or paste a copied image with Ctrl or Cmd and V.
- Pick an Aspect ratio: Free, 1:1, 4:3, 16:9, 3:2 or 9:16. The box reshapes itself around its centre and never grows when you choose a ratio.
- Drag the box to move it. Drag a corner or an edge handle to resize it; with a ratio selected the shape stays exact while you drag. The size under the box and the line "Result: width × height px" tell you what you will get, next to "Original".
- For precision, use the number fields: Left, Top, Width and Height, in pixels. With a ratio selected, changing the width changes the height to match. With Free selected, set both yourself, for example 3200 by 4000 and a Left of 1400 to centre it on a 6000 pixel wide photo.
- Without a pointer: the arrow keys move the box when it has the focus, and Shift with the arrows resizes it.
- Choose the Format and press "Crop and download". The file keeps your original name with "-cropped" added.
The image is opened and cut in your browser. The picture is not uploaded, so a private photo stays on your device.
Rotate and flip
The buttons "Rotate left" and "Rotate right" turn the picture 90 degrees, and "Flip horizontally" and "Flip vertically" mirror it. The crop box travels with the picture, so it keeps covering the same part of it. Turning a scan that came in sideways, or mirroring a selfie that was saved the wrong way round, is the typical use. All of it is exact: a quarter turn and a mirror only move pixels, they do not blur anything. "Reset" puts everything back.
Photos from phones and cameras often carry an orientation tag instead of being stored upright. The tool shows them upright, and the file it saves contains only the pixels, so the result has no leftover rotation tag to confuse other software.
Keeping the quality
- A crop does not resample. The preview on screen is a reduced copy, but the file is cut from the full-size picture, and the pixels inside the box are copied as they are. A 3000 by 3000 crop gives a 3000 by 3000 file.
- PNG is lossless. Every pixel is kept. The file may still be large for a photo.
- JPG and WebP are encoded again when saved. The quality slider starts at 92, which is high. Do all of your changes in one go, rotate, flip and crop together, because the tool applies them in a single save, and avoid opening the saved JPG to crop it a second time.
- JPG has no transparency, so transparent areas are filled with white. Choose PNG or WebP to keep them. The article on JPG, PNG and WebP compares the three.
- Do not enlarge. Cropping can only make a picture smaller. If a site wants a certain pixel size, crop to its ratio here and resize afterwards with the image toolkit, going down, not up.
- Metadata is not copied. The location, camera and other data stored in the original stay behind. If that is what you were after, read how to remove GPS location from photos.
Mistakes to avoid
- Choosing the ratio after placing the box. Pick the ratio first, then move the box. A new ratio shrinks the box around its centre, which may no longer cover the subject.
- Cropping the subject's head or feet to hit a ratio. If the subject does not fit, choose a looser ratio or leave the ratio on Free.
- Cropping a picture that was too small to start with. Fewer than a few hundred pixels on a side will look soft on a large screen.
- Mixing up 16:9 and 9:16. They are the same shape turned on its side. If your result is the wrong way, rotate it or choose the other ratio.
A short checklist
Know the ratio the destination wants, pick it before you place the box, check the "Result" size, keep the highest quality, crop and rotate in one go, and resize afterwards if a pixel size is required, never the other way round.