How to use it
- Set the original size. Type the width and height of your image, video or design. This pair defines the aspect ratio everything else is based on.
- Read the ratio. The tool instantly shows the simplified ratio (for example 1920 × 1080 → 16:9) and the decimal ratio (width ÷ height).
- Enter a new dimension. Type a new width or a new height and the other box is calculated for you, so the result keeps the exact same proportions.
Everything updates live as you type — there is no calculate button to press. Use ⇄ Swap to flip width and height when you switch between landscape and portrait.
How the ratio is worked out
An aspect ratio is just width compared to height, reduced to the smallest whole numbers. To simplify it, the calculator finds thegreatest common divisor (GCD) of the two values and divides both by it. For 1920 and 1080 the GCD is 120, so1920 ÷ 120 = 16 and 1080 ÷ 120 = 9, giving 16:9. Decimal inputs are scaled to whole numbers first so the simplification still works, and the decimal ratio (such as 1.7778 : 1) is shown alongside for precision.
Resizing without stretching
When you scale an image you must change width and height by the same factor, or it ends up squashed. That factor is what this tool applies: if you keep a 16:9 source and ask for a new width of 1280, the height becomes 1280 ÷ (16 ÷ 9) = 720 — the familiar 720p frame. Lock the proportions once and you can punch in any target size with confidence.
Common aspect ratios
- 16:9 — widescreen video, YouTube, most monitors and phones in landscape.
- 4:3 — older displays, many tablets and classic photography.
- 1:1 — square posts and profile pictures.
- 9:16 — vertical video for Reels, Shorts and TikTok.
- 3:2 — the native ratio of most DSLR and mirrorless cameras.
- 21:9 — ultrawide monitors and cinematic video.
Is it private?
Yes. The Aspect Ratio Calculator is plain JavaScript that runs entirely inside your browser tab. The dimensions you enter are never uploaded, logged or stored anywhere — there are no accounts and no tracking of your inputs. Once the page has loaded you can even use it offline.
Frequently asked questions
Why does the result show a dash?
The simplified ratio needs a valid original width and height that are both greater than zero. Fill in both boxes with positive numbers to see the ratio and decimal value.
Can it handle decimal dimensions?
Yes. Decimal widths and heights are accepted; the tool scales them to whole numbers internally before simplifying, and rounds computed dimensions to a few decimal places for readability.
Does it round pixels to whole numbers?
It shows the exact computed value, which can include a fraction. For pixel-perfect output you may want to round the result yourself, since screens only display whole pixels.
Computed dimensions are rounded for display; round to whole pixels before exporting if your software requires it.