21:9 Aspect Ratio Calculator
The 21:9 aspect ratio means 21 units wide for every 9 tall — ultrawide — with an honest footnote. It is used for Ultrawide monitors, cinematic video, wide website hero banners.
Scale it, keeping this ratio
Matching height: —
Matching width: —
Scaled values are rounded to whole pixels when they land within 0.01 px of an integer; otherwise the exact figure is shown — a video encoder or design tool may round slightly differently.
Pick an image file and this page reads its real pixel dimensions on your device and fills them in above. The file is never uploaded anywhere.
Common 21:9 resolutions
Every size in this table is exactly 21:9 — width × 9 equals height × 21 for each row, which you can check with the gcd method on the how-to page.
| Resolution | Width (px) | Height (px) | Typically used for |
|---|---|---|---|
| 840×360 | 840 | 360 | True 21:9 small |
| 1680×720 | 1680 | 720 | True 21:9 |
| 2520×1080 | 2520 | 1080 | True 21:9 (1080 tall) |
| 3360×1440 | 3360 | 1440 | True 21:9 (1440 tall) |
| 4200×1800 | 4200 | 1800 | True 21:9 |
| 5040×2160 | 5040 | 2160 | True 21:9 (2160 tall) |
Real ultrawide resolutions — and their real ratios
These are the panels actually sold as ultrawide. None of them is exactly 21:9:
| Resolution | Simplifies to | Decimal | Note |
|---|---|---|---|
| 2560×1080 | 64:27 | 2.370:1 | ≈2.370:1 — sold as "21:9" UW-FHD |
| 3440×1440 | 43:18 | 2.389:1 | ≈2.389:1 — sold as "21:9" UW-QHD |
| 3840×1600 | 12:5 | 2.400:1 | 2.4:1 — sold as "21:9" UW-QHD+ |
| 5120×2160 | 64:27 | 2.370:1 | ≈2.370:1 — sold as "21:9" UW-5K |
| 5120×1440 | 32:9 | 3.556:1 | ≈3.556:1 — sold as "32:9" super-ultrawide |
About the 21:9 ratio
Honest footnote: "21:9" is a marketing name, not an exact ratio. Simplified, 21:9 is really 7:3 (≈2.333:1). Most real ultrawide monitors are not exactly 7:3 at all — 2560×1080 simplifies to 64:27 (≈2.370:1), 3440×1440 to 43:18 (≈2.389:1) and 3840×1600 to 12:5 (2.4:1). The table below lists true 21:9 (7:3) sizes first, then the real ultrawide resolutions and what they actually simplify to.
To find a 21:9 size yourself: pick a width, then height = width × 9 ÷ 21. For whole-pixel results, choose a width that is a multiple of 21 — the height then comes out exact, with no rounding.
Frequently asked questions
What resolution is 21:9?
There is no single 21:9 resolution — the ratio describes a shape, not a size. Common 21:9 sizes include 840×360, 1680×720, 2520×1080 and the rest of the table above.
How do I convert a size to 21:9?
Keep one dimension and solve for the other: height = width × 9 ÷ 21, or width = height × 21 ÷ 9. The calculator at the top of this page is pre-filled with a 21:9 size so you can try it immediately.
Is 21:9 the same as its decimal?
The decimal form is width ÷ height (2.3333:1 for 21:9). The fraction form is exact; the decimal is an approximation that is handy for comparing shapes at a glance.