How to calculate an aspect ratio
Divide the width and the height by their greatest common divisor. For 1920 × 1080, the greatest common divisor is 120, so the ratio is 1920 ÷ 120 : 1080 ÷ 120 = 16:9. The decimal form is width ÷ height: 1920 ÷ 1080 = 1.78, written 1.78:1.
Screens and cameras are not always exact. 1366 × 768 works out to 683:384, which is within 0.05% of 16:9, so it is sold as a 16:9 display. The calculator shows the exact ratio and the closest standard one.
How to resize and keep the aspect ratio
New height = new width × original height ÷ original width
New width = new height × original width ÷ original height
Example. To shrink a 1920 × 1080 image to 1280 pixels wide: 1280 × 1080 ÷ 1920 = 720, so the new size is 1280 × 720. Both sides change by the same percentage (66.7%), so nothing is stretched. Use the Resize box above, or resize the file itself with the image resizer.
Does it work in inches, feet or centimeters?
Yes. An aspect ratio has no unit, because it compares two lengths in the same unit. Enter pixels for images and video, inches or centimeters for prints and screens, or feet for an LED wall or a projection screen. The resize and diagonal results come out in the same unit you entered.
Common aspect ratios
| Ratio | Decimal | Used for |
|---|---|---|
| 1:1 | 1:1 | Square posts, profile photos |
| 4:5 | 1:1.25 | Instagram portrait |
| 3:4 | 1:1.33 | Portrait photos, Instagram grid |
| 2:3 | 1:1.5 | Portrait photos, 4×6 prints |
| 9:16 | 1:1.78 | Stories, Reels, Shorts, TikTok |
| 5:4 | 1.25:1 | 8×10 prints, older monitors |
| 4:3 | 1.33:1 | Standard TV, iPad, phone photos |
| 3:2 | 1.5:1 | DSLR photos, 4×6 prints |
| 16:10 | 1.6:1 | Laptops and monitors |
| 16:9 | 1.78:1 | HD and 4K video, YouTube, TVs |
| 1.85:1 | 1.85:1 | Cinema, flat |
| 2:1 | 2:1 | Univisium, recent phones |
| 21:9 | 2.37:1 | Ultrawide monitors |
| 2.39:1 | 2.39:1 | Cinema scope, 3440×1440 ultrawides |
| 32:9 | 3.56:1 | Super ultrawide monitors |
Screen and video resolutions by aspect ratio
16:9 is the standard for HD and 4K video, TVs and most monitors. Laptops often use 16:10, ultrawide monitors use about 21:9, and vertical video for phones is 9:16.
| Aspect ratio | Common resolutions (pixels) |
|---|---|
| 16:9 | 640×360 · 1280×720 (720p) · 1920×1080 (1080p) · 2560×1440 (1440p) · 3840×2160 (4K UHD) · 7680×4320 (8K) |
| 16:10 | 1280×800 · 1440×900 · 1680×1050 · 1920×1200 · 2560×1600 |
| 4:3 | 640×480 · 800×600 · 1024×768 · 1600×1200 · 2048×1536 |
| 21:9 (64:27) | 2560×1080 · 5120×2160 |
| 21:9 (43:18) | 3440×1440 |
| 32:9 | 3840×1080 · 5120×1440 |
| 3:2 | 3000×2000 · 6000×4000 (24 MP camera) |
| 1:1 | 1080×1080 |
| 4:5 | 1080×1350 |
| 9:16 | 720×1280 · 1080×1920 · 2160×3840 |
| 256:135 (≈1.90:1) | 4096×2160 (DCI 4K cinema) |
Monitors sold as 21:9 are not exactly 21:9 (2.33:1). 2560 × 1080 is 64:27 (2.37:1) and 3440 × 1440 is 43:18 (2.39:1).
Aspect ratios for YouTube, Instagram and TikTok
YouTube's standard player on a computer is 16:9, Shorts are vertical, and Instagram Stories, Reels and TikTok videos fill a 9:16 phone screen. Instagram feed posts can be square, 4:5 or 3:4 portrait, or 1.91:1 landscape.
| Platform | Aspect ratio | Size (pixels) | Source |
|---|---|---|---|
| YouTube video | 16:9 | 1920×1080, 2560×1440, 3840×2160 | YouTube Help |
| YouTube Shorts | Vertical, 9:16 | 1080×1920 | YouTube Help |
| Instagram feed | 1:1, 4:5, 3:4, 1.91:1 | 1080×1080, 1080×1350, 1080×1440, 1080×566 | Instagram size guide |
| Instagram Stories and Reels | 9:16 | 1080×1920 | Instagram size guide |
| TikTok | 9:16 (also 1:1, 16:9) | at least 540×960 | TikTok Ads Help |
To crop or pad an image to these sizes, use the social media image resizer.
Aspect ratio of print and paper sizes
A 4×6 print has the same 2:3 shape as most camera photos, so it prints without cropping. An 8×10 is 4:5, which crops the long side of a 2:3 photo. US Letter paper (8.5×11 in) is 17:22. A4 and the other ISO A sizes keep a 1:√2 ratio, so halving a sheet gives the same shape.
| Print or paper size | Aspect ratio | Decimal |
|---|---|---|
| 4×6 in | 2:3 | 1:1.5 |
| 5×7 in | 5:7 | 1:1.4 |
| 8×10 in | 4:5 | 1:1.25 |
| 8.5×11 in (US Letter) | 17:22 | 1:1.29 |
| 11×14 in | 11:14 | 1:1.27 |
| 16×20 in | 4:5 | 1:1.25 |
| 24×36 in | 2:3 | 1:1.5 |
| A4, A3 and other A sizes | 1:√2 | 1:1.414 |
Movie aspect ratios, including IMAX
Most feature films are shown at 1.85:1 or 2.39:1. IMAX digital theaters use 1.90:1, and IMAX 70mm film projects a taller 1.43:1 image, usually for selected scenes.
| Format | Aspect ratio |
|---|---|
| Academy ratio (classic films) | 1.375:1 |
| Widescreen “flat” | 1.85:1 |
| Anamorphic “scope” | 2.39:1 |
| IMAX digital | 1.90:1 |
| IMAX 70mm film | 1.43:1 |
| HDTV and streaming | 16:9 (1.78:1) |
Screen width and height from the diagonal
Height = diagonal ÷ √(r² + 1)
Width = height × r, where r = width ÷ height
Example. A 27-inch 16:9 monitor: r = 1.778, height = 27 ÷ √(1.778² + 1) = 13.2 in, width = 13.2 × 1.778 = 23.5 in. Enter any diagonal in the calculator to get the width and height for the current ratio.
Sources
- YouTube Help, Recommended upload encoding settings (16:9 standard and resolutions), checked October 2026
- YouTube Help, Get started creating YouTube Shorts (vertical, up to 3 minutes), checked October 2026
- TikTok Ads Help, TikTok Auction In-Feed Ads (9:16 recommended, minimum sizes), last updated June 2026
- IMAX and Aspect ratio (image), Wikipedia (film formats)
- ISO 216 (A paper sizes, 1:√2)