Aspect Ratio Calculator
Enter a width and height to get the ratio, or lock a ratio to resize.
A free online aspect ratio calculator — type any width and height to see the simplified ratio and its common name, or lock a ratio and change one dimension to calculate the other. Upload an image to detect its exact ratio automatically. No signup, runs entirely in your browser.
Lock ratio
Changing one dimension recalculates the other
Simplified ratio
Common ratios
Or detect the ratio from an image
What is an aspect ratio?
An aspect ratio is the proportional relationship between an image or screen's width and height, written as two numbers separated by a colon (like 16:9). It describes shape, not size — a 1920×1080 photo and a 320×180 thumbnail share the same 16:9 ratio even though one has far more pixels. Aspect ratio matters whenever you're cropping, resizing, or exporting for a specific placement (a video player, a social media post, a print size) that expects a particular shape.
Example: resizing an image with a locked ratio
Say you have a 16:9 banner at 1920×1080px and need it at exactly 800px wide without distorting it. Turn on Lock ratio, type 800 into Width, and Height instantly becomes 450 — preserving the exact 16:9 shape. This is the same math a design tool does when you resize an image with "constrain proportions" checked.
Common aspect ratios and where they're used
- 16:9 — widescreen video, YouTube, most monitors and TVs
- 4:3 — older TVs and monitors, some presentation slides
- 1:1 — square, Instagram feed posts
- 3:2 — classic 35mm photography, most DSLR sensors
- 21:9 — ultrawide monitors, cinematic video
- 9:16 — vertical video: Reels, TikTok, Shorts, Stories
Why real-world images are rarely an exact ratio
A photo that's "16:9" is often something like 1918×1080 rather than a perfectly clean 1920×1080, because of how cropping and compression tools round pixel counts. This calculator detects a close match within a small tolerance and labels it as the named ratio, rather than requiring pixel-perfect numbers before it recognizes what you're looking at.
Frequently asked questions
How do I calculate an aspect ratio?
Type a width and height into the two fields — the simplified ratio (like 16:9) appears instantly below, along with the closest common named ratio if your dimensions are close to one. No calculate button needed.
How do I resize an image while keeping the aspect ratio?
Turn on Lock ratio, then change either the width or height — the other dimension recalculates automatically to preserve the exact same ratio. This is the fastest way to find, say, what height a 1200px-wide image needs at a 16:9 ratio.
Can I detect the aspect ratio of an image I already have?
Yes. Upload, drag, or paste an image and its exact pixel width and height are read automatically and dropped into the calculator, showing you its simplified ratio right away.
What do the aspect ratio presets mean?
16:9 is the standard widescreen video/monitor ratio. 4:3 is the older "square-ish" TV and monitor standard. 1:1 is a perfect square (Instagram posts). 3:2 is common in photography (35mm film and most DSLRs). 21:9 is ultrawide cinematic. 9:16 is vertical video (Reels, Shorts, Stories).
Is my image uploaded anywhere?
No. Reading an image's dimensions happens locally in your browser — the file is never sent to a server.
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