What width is 720 tall at 16:9?

720 x 16 / 9 = 1280px. Use aspect-ratio: 16 / 9.

How to keep 720 tall from stretching?

Set height: 720px paired with the computed width, and aspect-ratio: W / H on the container; use object-fit for inner media.

720 at this size works vertical or horizontal depending on ratio - check the table for portrait inversions like 9:16.

A 720px-tall frame is used in many layouts. The table below lists the exact partner width at every ratio RatioCalc supports.

Ratio	Width for 720	Pair	CSS
16:9	1280px	1280x720	aspect-ratio: 16 / 9
4:3	960px	960x720	aspect-ratio: 4 / 3
1:1	720px	720x720	aspect-ratio: 1 / 1
9:16	405px	405x720	aspect-ratio: 9 / 16
21:9	1680px	1680x720	aspect-ratio: 21 / 9
3:2	1080px	1080x720	aspect-ratio: 3 / 2
16:10	1152px	1152x720	aspect-ratio: 16 / 10
4:5	576px	576x720	aspect-ratio: 4 / 5
2:1	1440px	1440x720	aspect-ratio: 2 / 1
239:100	1721px	1721x720	aspect-ratio: 239 / 100
32:9	2560px	2560x720	aspect-ratio: 32 / 9
5:4	900px	900x720	aspect-ratio: 5 / 4
2:3	480px	480x720	aspect-ratio: 2 / 3
18:9	1440px	1440x720	aspect-ratio: 18 / 9
5:3	1200px	1200x720	aspect-ratio: 5 / 3
1:2	360px	360x720	aspect-ratio: 1 / 2

width = 720 x rw / rh

// e.g. 9:16 at 720 tall is 405px

Print tip: at 720px, verify with w = 720 x rw / rh before print - 1px matters on narrow banners.