Every platform wants a different shape for the same photo, this simplifies a ratio, fills in a missing dimension, or works out exactly what a crop will cost you.
Free camera tool
Aspect Ratio Calculator
Simplify a ratio, solve for a missing dimension, or work out the largest crop that fits a target ratio.
Runs entirely in your browser. Nothing you enter is sent anywhere.
Why a "centered" crop, specifically
The crop mode here always centers the crop box on the original frame, trimming equally from both sides, since that's the safest default when you don't know the subject's exact position. If your subject sits off-center, you'll usually want to shift the crop box toward it rather than use these numbers as an exact final crop, treat the trimmed-pixels figures as your starting point, then nudge from there in your editor.
Aspect ratio calculator FAQ
What is an aspect ratio?
It's the relationship between an image's width and height, written as two numbers like 3:2 or 16:9. Two images can be completely different sizes in pixels and still share the same aspect ratio, what matters is the proportion between width and height, not the absolute dimensions.
How do I simplify a resolution into a ratio?
Divide both the width and height by their greatest common divisor, 1920x1080 divided by their GCD of 120 simplifies to 16:9. The "Simplify a ratio" mode above does this automatically and also matches your numbers against the nearest standard photography or video ratio.
Why do different platforms want different aspect ratios?
Each format is optimized for how it's actually viewed, 16:9 matches widescreen displays, 9:16 fills a phone screen for vertical video, 4:5 uses more of a phone screen in a feed than a square 1:1 crop does. Posting the wrong ratio usually means the platform crops or letterboxes it for you, so matching the ratio up front keeps you in control of the framing.
What happens to the pixels I lose when cropping to a ratio?
They're simply discarded, permanently, unless you're working from a copy. The "Crop to a ratio" mode shows exactly how many pixels get trimmed from each side with a centered crop, so you know in advance whether an off-center subject will end up too close to the new edge before you commit to the crop in your editor.
What's the most common aspect ratio for print versus screen?
Most cameras shoot 3:2 (matching 35mm film) or 4:3, but standard photo print sizes like 4x6 and 8x10 don't actually match either ratio exactly, which is the classic reason part of a photo gets cropped off at the print shop. Screens vary by use, 16:9 for video and most monitors, 9:16 or 4:5 for phone-first content.
Free aspect ratio calculator by ANUPRESS
A ratio is a shape, not a size
1920×1080 and 3840×2160 are wildly different file sizes that happen to share the exact same shape, 16:9, because ratio only describes the relationship between width and height, never their absolute values. That’s why a resolution can be simplified down to a small, recognizable ratio in the first place, most of the number is redundant once you know the proportion.
Every platform’s preferred ratio comes from how it’s actually viewed
16:9 exists because it matches widescreen displays, 9:16 exists because it fills a phone screen held vertically, 4:5 exists because it uses more of a feed than a square crop does before someone has to tap to see the rest. Post the wrong shape and the platform crops or letterboxes it for you, on its terms, not yours, which is the real reason it’s worth checking the ratio before exporting rather than after.
A centered crop is a safe default, not a finished decision
The crop mode above always trims equally from both sides, the only sensible default when the tool has no idea where your subject actually is in the frame. If the subject sits off-center, the trimmed-pixel numbers are still useful, they tell you exactly how much room you have to work with, but the final crop position is a call worth making by eye in your editor, not something to accept as-is from any calculator.