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Why cropping to a new ratio loses pixels, and how many
Every photo has an aspect ratio, the width divided by the height. A 3:2 photo is one and a half times wider than it is tall, a 16:9 photo is nearly twice as wide as it is tall, and a 1:1 photo is square. Cameras, screens, and print sizes all favour different ratios, so photographers constantly crop one ratio into another. The catch is that cropping to a new ratio always discards pixels from at least one side, and the amount discarded depends on how different the two ratios are. A small change, such as 3:2 to 4:3, costs little. A large change, such as 3:2 to a tall 9:16 portrait for a phone screen, can throw away more than half the image.
The rule for the largest possible crop is simple. Compare your photo’s ratio with the target ratio. If your photo is wider than the target, the crop keeps the full height and trims the width until the ratio matches. If your photo is taller than the target, the crop keeps the full width and trims the height. The side that already matches stays untouched, which is why this is the largest crop: any larger crop in the other direction would break the ratio. This calculator applies that rule and shows the crop dimensions in pixels plus the percentage of pixels kept, so you can judge whether the result still has enough resolution for your purpose.
How to use this aspect ratio crop size calculator
Enter your photo’s pixel width and height, then choose the target ratio. Common targets include 16:9 for video and wide screens, 4:3 for many screens and prints, 3:2 for classic photo prints, 1:1 for social media squares, 4:5 for portrait posts, and 9:16 for vertical phone video. The tool shows the largest crop dimensions and the percentage of pixels kept. For example, a 6000 by 4000 pixel photo cropped to 16:9 becomes 6000 by 3375 pixels, keeping about 84 percent of the pixels, because the width stays full and only the height shrinks. Cropped to square, the same photo becomes 4000 by 4000 pixels, keeping about 67 percent.
Worked examples help you plan shoots. A 4000 by 6000 portrait photo cropped to 3:2 landscape thinking is impossible without rotating, but cropped to a 3:2 portrait shape it becomes 4000 by 2667 pixels, again keeping about 67 percent. A photo destined for both a wide website banner and a square social post should be shot with room around the subject on all sides, because the square crop will cut the sides and the banner crop will cut the top and bottom. If you know the target ratios before you shoot, leave that breathing room in the frame, and cropping becomes painless instead of destructive.
Ratio choices for common outputs
Print sizes carry their own ratios, and matching them in advance saves quality. An 8 by 10 inch print is 4:5, a 5 by 7 inch print is 5:7, and an 11 by 14 inch print is about 11:14, none of which match a 3:2 camera file exactly. That is why print labs crop a little from every order unless you ask for the full frame with white borders. Social platforms are stricter: a square post wants 1:1, a portrait post looks best near 4:5, and a story or reel wants 9:16. Video platforms want 16:9 for standard video and 9:16 for short vertical video. Check the platform’s current ratio before you export, because platforms change their preferred sizes often, and an old preset can silently crop your subject’s head or feet.
Three habits protect your images. First, shoot slightly wider than you think you need whenever the scene allows it, because you can always crop later but you can never recover pixels you never recorded. Second, keep important subjects away from the edges of the frame, since every crop eats edges first and a subject touching the border will be cut. Third, after cropping, check the remaining pixel count against your output: a 2000 pixel wide crop prints well at 8 inches wide at 250 DPI, but it will look soft at 20 inches wide. Use this calculator before you crop, not after, and you will know exactly what each ratio costs while you still have time to recompose or reshoot.
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