Aspect Ratio Calculator

About Aspect Ratio Calculator

How Aspect Ratio Calculation Works

Aspect ratio is simply width divided by height, then reduced to the smallest whole-number pair using the greatest common divisor (GCD). The formula is:

Ratio = Width / GCD(Width, Height) : Height / GCD(Width, Height)

Worked example: For 1920 x 1080 pixels, GCD(1920, 1080) = 120. So the ratio is 1920/120 : 1080/120 = 16:9. For 3840 x 2160 (4K UHD), GCD is 240 and the ratio is again 16:9 - 4K is just a higher-resolution version of the same rectangle.

To resize while keeping the shape identical:

New Height = New Width x (Original Height / Original Width)

Worked example: Scaling a 16:9 image down to 1280px wide: 1280 x (9/16) = 720px tall. The new dimensions are 1280 x 720. Going the other way, a target height of 900px on a 4:3 source gives 900 x (4/3) = 1200px wide.

Rounding matters. If you compute a dimension and get 719.4, round to 720 - most image and video encoders refuse non-integer sizes, and some codecs (H.264, VP9) require dimensions divisible by 2 or 16.

Common Aspect Ratios Reference

Ratio	Decimal	Common Resolutions	Where It Is Used
16:9	1.778	1920x1080, 2560x1440, 3840x2160	HD/4K monitors, TVs, YouTube, most video content
16:10	1.600	1920x1200, 2560x1600	MacBook displays, productivity monitors
4:3	1.333	1024x768, 1600x1200	Classic CRT TVs, iPad, PowerPoint presentations
21:9	2.333	2560x1080, 3440x1440	Ultrawide monitors, cinematic content
32:9	3.556	5120x1440	Super ultrawide monitors
1:1	1.000	1080x1080	Instagram posts, profile pictures, album covers
9:16	0.563	1080x1920	TikTok, Instagram Reels, YouTube Shorts, Stories
3:2	1.500	6000x4000, 2160x1440	DSLR photography, Surface laptops, 35mm film
2:3	0.667	1000x1500	Pinterest pins, portrait photography
4:5	0.800	1080x1350	Instagram portrait posts (takes up more feed space)
3:4	0.750	1080x1440	Instagram 2026 new vertical format
2.39:1	2.390	2048x858	Anamorphic cinema (Hollywood widescreen)
1.85:1	1.850	1998x1080	Standard theatrical widescreen

What Are the Recommended Aspect Ratios for Social Media?

Meta, YouTube, and TikTok all publish target ratios in their creator documentation - uploading outside those specs means your image gets cropped, letterboxed, or compressed further. The table below reflects current platform guidance as of 2026, with 4:5 (1080 x 1350) the dominant portrait standard on Instagram since Meta started favouring vertical content for feed reach.

Platform	Content Type	Ratio	Resolution
YouTube	Video	16:9	1920x1080 or 3840x2160
YouTube Shorts	Short video	9:16	1080x1920
Instagram	Square post	1:1	1080x1080
Instagram	Portrait post	4:5	1080x1350
Instagram	Story / Reel	9:16	1080x1920
TikTok	Video	9:16	1080x1920
Twitter/X	Image	16:9	1200x675
Facebook	Shared image	1.91:1	1200x630
LinkedIn	Post image	1.91:1	1200x627
Pinterest	Pin	2:3	1000x1500

Portrait 4:5 posts occupy roughly a third more screen on a phone than 1:1 squares, which is why Meta's guidance has shifted in that direction. Feed carousels still support 1:1 for backwards compatibility, but new single-image posts perform better at 4:5 in Meta's own engagement reports.

Aspect Ratios in Film and TV

Cinema and television have cycled through dozens of aspect ratios. The ones still in use today cluster around six common values:

• Academy ratio (1.375:1): The SMPTE standard for 35mm film from 1932 through the 1950s. Almost square, very close to 4:3.
• Flat widescreen (1.85:1): The most common theatrical ratio in the US since the 1950s. Used by most dramas and comedies shot on spherical lenses.
• Anamorphic scope (2.39:1): The wide cinematic look used in action films, epics, and sci-fi. Shot with anamorphic lenses that optically squeeze a wider image onto a standard-width film frame, then unsqueeze in projection.
• IMAX (1.43:1): The taller IMAX format that fills the entire IMAX screen. Films like Oppenheimer (2023) and Dunkirk (2017) use selective IMAX sequences shot on 65mm or 70mm film.
• 4:3 television (1.33:1): The pre-HD broadcast standard. Shows like The Wire and early seasons of 24 were originally composed for 4:3.
• 16:9 HDTV (1.78:1): The current broadcast and streaming standard, and the shape every HDMI device expects.

Why Did 16:9 Become the Standard?

16:9 won because it is the geometric mean of the two extremes that TV had to cover: 4:3 (old tube television) and 2.39:1 (widescreen cinema). Dr. Kerns Powers of the SMPTE Working Group on High-Definition Electronic Production first proposed the ratio in 1984. He cut out rectangles with equal areas shaped to match each popular aspect ratio (4:3, 15:9, 1.85:1, 2.35:1), overlapped them at their centres, and found that every rectangle fit within a common outer rectangle with a 1.77:1 ratio and covered a common inner rectangle with the same ratio. That number rounds to 16:9.

The practical consequence is symmetry: a 4:3 show on a 16:9 screen wastes the same amount of screen as a 2.39:1 film on a 16:9 screen. No other single ratio balances the extremes as neatly, which is why SMPTE, the ITU, and the ATSC all adopted 16:9 in the 1990s. Every modern TV, monitor, phone, laptop, and game console inherits that decision.

Common Mistakes and How to Avoid Them

• Stretching instead of letterboxing. If your source is 4:3 and the target is 16:9, never stretch - add black bars (pillarboxing) to preserve the shapes on screen.
• Forgetting pixel aspect ratio. Some legacy formats (DV-PAL, anamorphic DVD) use non-square pixels. A 720x576 DV-PAL frame displays as 16:9 because each pixel is 1.42x wider than it is tall. Always check whether the pixels are square before computing a ratio.
• Uploading the wrong ratio to a platform. Instagram will crop a 16:9 image uploaded as a feed post. Record in 4:5 or 1:1 from the start, or pre-crop before upload.
• Odd-numbered dimensions. H.264 requires dimensions divisible by 2. H.265 and VP9 are even stricter. If the calculator returns 719, round to 720.
• Ignoring safe areas. TV broadcast still assumes a title-safe area about 80% of the frame. Text placed at the edges of a 16:9 export can get cut off on some screens.

Once you have your target dimensions, the image resizer can scale image files to the exact pixel size. For checking your display's actual resolution and pixel density, try the screen resolution checker or the PPI calculator.

All calculations run locally in your browser. No images or data are uploaded.

Sources

• Wikipedia - 16:9 aspect ratio (Kerns Powers / SMPTE derivation)
• SMPTE - Society of Motion Picture and Television Engineers
• YouTube Help - Video resolution and aspect ratios
• Instagram Help - Photo and video specifications
• TikTok Support - Video resolutions and specs
• MDN - CSS aspect-ratio property
• ITU-R BT.709 - Parameter values for the HDTV standards