Type a width and a height and the tool reduces them to the simplest aspect ratio, such as 1920×1080 → 16:9, and names it when it is a familiar one. Below that, enter a new width or a new height and it works out the other dimension so the proportions stay identical. Everything runs in your browser.
Decimal ratio: 1.7778 : 1
Resize keeping this ratio
Height becomes: —
Width becomes: —
How it works
The ratio is found by dividing both numbers by their greatest common divisor (GCD). For 1920 and 1080 the GCD is 120, so the ratio reduces to 16:9. The decimal ratio (width ÷ height) is shown too — 1.7778 : 1 for 16:9 — which is handy when a value does not reduce to a tidy pair.
To resize, the tool holds width ÷ height constant. Give it a new width and the new height is newWidth × height ÷ width; give it a new height and it does the reverse. So 1920×1080 scaled to a width of 1280 gives a height of 720 — the same 16:9. Dimensions are treated as whole pixels when reducing the ratio, while the decimal ratio stays exact for unusual sizes.
Practical examples
Full HD reduces to 16:9
Enter 1920 × 1080 and the ratio is 16:9 — the widescreen standard for TVs, monitors and YouTube. The decimal reads 1.7778 : 1.
Resize a photo without distortion
A 4000 × 3000 photo is 4:3. To fit a 1200 px-wide slot, enter 1200 as the new width and the tool returns 900 px tall — same proportions, no stretching.
Vertical video for reels
Enter 1080 × 1920 and you get 9:16, the vertical format for Reels, TikTok and Stories — the inverse of 16:9.
Frequently asked questions
What is an aspect ratio?
It is the proportional relationship between width and height, written as two numbers like 16:9. It tells you the shape of an image or screen independent of its actual size, so 1280×720 and 1920×1080 are both 16:9.
How is the ratio simplified?
By dividing both dimensions by their greatest common divisor. 1600 and 900 share a GCD of 100, so they reduce to 16:9. This is the same method as simplifying a fraction, which is exactly what a ratio is.
What does the decimal ratio mean?
It is width divided by height. 16:9 is about 1.78, 4:3 is about 1.33, and a square is 1.0. The decimal is useful when the whole-number ratio is awkward — for example 1000×613 does not reduce neatly but is 1.63 : 1.
How do I resize an image without stretching it?
Keep the aspect ratio fixed. Enter your original width and height, then type the new width you need — the tool gives the matching height (or vice versa). Using those two numbers preserves the proportions exactly.
What are the common aspect ratios?
16:9 (widescreen video and monitors), 4:3 (older screens and many cameras), 3:2 (35 mm photography), 1:1 (square, Instagram), 9:16 (vertical video) and 21:9 (ultrawide/cinema). The tool labels these when your numbers match.
Why does my ratio show odd numbers like 683:384?
Because those dimensions do not share a large common divisor, so the simplest whole-number form is still large. In that case rely on the decimal ratio to compare it with a standard — 683:384 is about 1.78, i.e. effectively 16:9.
Does it work for print sizes or only pixels?
Any units work, as long as width and height use the same one. A 30 × 20 cm print is 3:2, the same as a 3000 × 2000 px photo. The ratio ignores the unit; only the proportion matters.
Can I enter decimals?
Yes, and the decimal ratio stays exact. For the simplified whole-number ratio the dimensions are rounded to the nearest pixel first, since screen and image sizes are whole numbers. You can type 6,5 or 6.5.
Is anything I enter uploaded?
No. The calculation runs entirely in your browser; no image and no numbers are sent anywhere, and analytics never receives the values.
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