Smallest whole-pixel size 3 × 7.
In CSS: aspect-ratio: 9 / 21. Rotated it becomes 21:9.
Where 9:21 is used
Sony Xperia, a handful of cinema-oriented phones.
Chosen so anamorphic footage plays full-screen without letterboxing.
Rendered live with aspect-ratio: 9 / 21.
9:21 resolutions
Every size below is exactly 9:21 — no rounding. Sizes marked as a standard are named display resolutions.
| Resolution | Width | Height | Megapixels | Standard |
|---|---|---|---|---|
| 162 × 378 | 162 | 378 | 0.06 | — |
| 165 × 385 | 165 | 385 | 0.06 | — |
| 168 × 392 | 168 | 392 | 0.07 | — |
| 171 × 399 | 171 | 399 | 0.07 | — |
| 174 × 406 | 174 | 406 | 0.07 | — |
| 177 × 413 | 177 | 413 | 0.07 | — |
| 180 × 420 | 180 | 420 | 0.08 | — |
| 480 × 1120 | 480 | 1120 | 0.54 | — |
| 720 × 1680 | 720 | 1680 | 1.21 | — |
| 960 × 2240 | 960 | 2240 | 2.15 | — |
| 1080 × 2520 | 1080 | 2520 | 2.72 | — |
| 1200 × 2800 | 1200 | 2800 | 3.36 | — |
| 1440 × 3360 | 1440 | 3360 | 4.84 | — |
| 1920 × 4480 | 1920 | 4480 | 8.6 | — |
| 3840 × 8960 | 3840 | 8960 | 34.41 | — |
Using 9:21 in CSS
/* Modern — one line */
.box { aspect-ratio: 9 / 21; }
/* With a fixed width */
.box { width: 100%; max-width: 960px; aspect-ratio: 9 / 21; }
/* Legacy padding-top hack, if you still need it */
.box-legacy { position: relative; }
.box-legacy::before { content: ""; display: block; padding-top: 233.3333%; }
.box-legacy > * { position: absolute; inset: 0; }Questions about 9:21
What resolution is 9:21?
9:21 is a ratio, not a fixed resolution — any size where width ÷ height equals 0.4286 qualifies. The smallest whole-pixel pair is 3 × 7, and common ones include 720 × 1680, 960 × 2240, 1080 × 2520, 1200 × 2800.
What is 9:21 used for?
Sony Xperia, a handful of cinema-oriented phones.
How do I set 9:21 in CSS?
Use the aspect-ratio property: aspect-ratio: 9 / 21;. The element then keeps that shape at any width. It is supported in every current browser.
What is 9:21 the other way round?
Rotated to landscape it becomes 21:9 — the same shape, turned 90 degrees.
How do I calculate a 9:21 height from a width?
Multiply the width by 2.333333. For example 1080 × 2.333333 = 2520. The calculator does it both directions.