Aspect Ratio Calculator
Works out the missing dimension for a target ratio and lists the standard sizes it matches.
Works out the other dimension for a given ratio, tells you which standard ratio a size is (within a tolerance, because real sizes are not tidy), and computes the largest box of that ratio that fits inside another one.
Ratio
HD video, most displays, YouTube.
16:9 · 1.7778:1
Solve
1920 × 1080
Actual ratio
1.7778:1
Rounding error
0.000%
Preview
What this size is
- 16:90.000%HD video, most displays, YouTube.
Matched by tolerance rather than by exact reduction — 1366×768, the most common laptop resolution ever shipped, is 683:384 and an exact matcher would call it nothing.
Fit inside a box
Largest fit: 1280 × 720
Snapped to even pixels: H.264 chroma subsampling works on 2×2 blocks and an odd dimension is either rejected or silently padded.
Standard sizes
- 1280×720 · 16:9
- 1920×1080 · 16:9
- 3840×2160 · 16:9
- 1366×768 · 16:9
- 2560×1664
- 1179×2556
- 1080×1080 · 1:1
- 1080×1350 · 4:5
- 1080×1920 · 9:16
- 1200×630 · 1.91:1
- 1280×720 · 16:9
- 2480×3508
- 794×1123
- 2550×3300
How to use it
Set the ratio
Type it, or take a preset — 16:9, 4:3, 1:1, 9:16, 2.39:1 and the rest. The reduced form and the decimal are shown beside it.
Give the side you know
The other side is computed, along with the ratio you actually get after rounding and how far that is from the ratio you asked for.
Or fit it inside a box
Give the container and get the largest size of your ratio that fits, snapped to even pixels — H.264 works on 2×2 chroma blocks, and an odd dimension is either rejected or silently padded.
Common questions
What does the rounding error mean in practice?
That whole pixels cannot hit your ratio exactly. On a video it shows up as a black hairline along one edge after encoding — better to know before the export than after.
Why does 1366×768 not come out as 16:9?
Because it is not — exactly, it is 683:384. It is also the most common laptop resolution ever shipped. Matching by tolerance rather than by exact reduction is what lets this call it 16:9 with the error shown, which is more useful than calling it nothing.
Is `aspect-ratio` in CSS the same thing?
It is the ratio, and the copy button gives you the declaration. What it does not do is pick pixel dimensions — the browser sizes the element from its container, which is usually what you want on a page and never what you want for an export.
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