Free Aspect Ratio Calculator

Find the aspect ratio of any resolution, or scale dimensions proportionally. Recognizes common presets like 16:9, 4:3, and 1:1.

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Result
Enter your details on the left, then press Calculate.

What is this calculator for?

You're cropping a YouTube thumbnail and the platform wants 1280×720 (16:9). You have a beautiful 4032×3024 photo (4:3) — cropping for 16:9 will cut off significant content. Or you're resizing a banner image to fit a different platform's requirements. The aspect ratio calculator handles the math: given an aspect ratio and one dimension, what's the other dimension? Or given two dimensions, what's the ratio in simplest form?

Common aspect ratios. 16:9: standard HD video and modern TV. 4:3: traditional TV (pre-HD), some computer monitors. 3:2: most DSLR cameras, 35mm film. 1:1: Instagram square, square album art. 21:9: ultrawide cinematic, ultrawide monitors. 9:16: vertical video for TikTok/Reels/Stories. 2.39:1: cinema widescreen. Each platform has preferred ratios: YouTube 16:9, Instagram square (1:1) or portrait (4:5), TikTok and Reels 9:16, Twitter posts 16:9 or 1:1, LinkedIn 1.91:1 for shared images.

This calculator computes missing dimensions from known dimensions and ratios, finds simplified ratios from any two numbers, and shows common ratio names. Use for image cropping, video formatting, design layout, and TV/monitor purchasing decisions.

How to use this calculator

Enter two of three: width, height, or aspect ratio. The calculator returns the third.

For resizing to a target ratio: enter the original dimensions and target ratio. The calculator outputs new dimensions plus the crop loss (how much of the original area is cut). Resizing a 4032×3024 photo to 16:9: crops to 4032×2268 (loses 25% of height) or 5376×3024 (impossible — exceeds original width). Always crop in the direction that loses less content.

For finding the closest standard ratio: enter any two dimensions and the calculator simplifies (uses GCD) and identifies common ratio names.

Understanding your results

The calculator returns the missing dimension, the simplified ratio, and identifies common ratio names when matching.

Aspect ratio math. Ratio = width / height. 16:9 = 1.778. 4:3 = 1.333. 1:1 = 1.000. 9:16 = 0.5625. 21:9 = 2.333. To check if two dimensions match a ratio: divide width by height and compare to ratio's decimal. 1920×1080: 1.778 = 16:9. 3840×2160: 1.778 = 16:9 (4K UHD). 1366×768: 1.778 = 16:9 (laptop standard).

The crop trade-off. Cropping from 4:3 to 16:9 loses 25% of vertical content. Cropping from 16:9 to 1:1 loses 44% (cropping to a square from widescreen is brutal). Cropping from 1:1 to 16:9 loses 44% of horizontal content. The lesson: shoot in the widest aspect ratio you might need (16:9 or wider), then crop down to narrower ratios as needed. Cropping a wide image to square loses content; uncropping a square image to wide can't recover content.

Platform-specific dimensions for 2024-25. YouTube thumbnail: 1280×720 (16:9). Instagram feed: 1080×1080 (1:1) or 1080×1350 (4:5). Instagram Story/Reel: 1080×1920 (9:16). TikTok: 1080×1920 (9:16). Twitter/X feed: 1200×675 (16:9). LinkedIn shared image: 1200×627 (1.91:1). Facebook feed: 1200×630 (1.91:1). Pinterest pin: 1000×1500 (2:3). When designing creative for multiple platforms: design at the highest resolution for the largest format, then crop down.

The 8K/4K/HD reality. 8K UHD: 7680×4320 (16:9, 33 megapixels). 4K UHD: 3840×2160 (16:9, 8 megapixels). 1080p HD: 1920×1080. 720p HD: 1280×720. 480p (DVD quality): 640×480 (4:3). 360p (low quality): 480×360. Each step up is roughly 4x more pixels. 8K requires substantial bandwidth and storage; not yet practical for most online video (YouTube and others typically max at 4K for actual content delivery).

A worked example

Marcus is creating thumbnails for a YouTube video. The original screenshot from his footage is 1920×1080 (16:9). He wants to create matching versions for: YouTube thumbnail (16:9 unchanged), Instagram square (1:1), Instagram vertical (4:5), TikTok vertical (9:16).

YouTube thumbnail (16:9): 1920×1080 fits as-is. Or 1280×720 if he wants smaller file. Same ratio; just resize.

Instagram square (1:1): from 1920×1080, the natural crop is 1080×1080. He centers the subject in the middle of the original 1920px width, cropping 420px from each side. Loses 44% of the horizontal content (1920×1080 has 2.07M pixels; 1080×1080 has 1.17M pixels — 56% retained, 44% cropped).

Instagram vertical (4:5): from 1920×1080, he wants a vertical 1080×1350. But 1080×1350 has height > width of original (1080 < 1920) — so the 1080 width works (he just uses central 1080 of the 1920 width), but height 1350 needs to come from the existing 1080 height of his image — impossible without adding canvas. He has two options: (a) crop to 1080×1080 (square) and accept that as final, (b) compose differently for Instagram vertical — re-shoot at vertical orientation, or use a different image with vertical content. Stretching the existing image to fit doesn't work without distortion or canvas-extending.

TikTok vertical (9:16): similar issue. Original 1920×1080 is horizontal. To produce 1080×1920 vertical from this: again impossible without adding canvas or reshooting. The lesson: vertical platforms (Instagram Story/Reel, TikTok) often require dedicated vertical-shot content. Don't try to retrofit horizontal content into vertical without significant compromise.

Practical strategy: shoot in 16:9 for primary platform use (YouTube, Twitter, LinkedIn, web). For Instagram square: crop horizontal content. For vertical platforms: shoot dedicated vertical content (most modern phones can shoot 9:16 video natively). Content creators with multi-platform needs increasingly shoot horizontal AND vertical simultaneously — same scene captured at both orientations to maximize platform reach.

Related resources

For pixel-level precision in design work, see Pixel Ruler. For color in design work, the Color Converter and Color Picker. For general unit conversions, the Unit Converter. The various social media platforms publish current image dimension specifications on their respective creator and developer documentation.

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Frequently asked questions

What are common aspect ratios for social media?

YouTube / video: 16:9 (1920x1080, 1280x720). Instagram square: 1:1 (1080x1080). Instagram portrait: 4:5 (1080x1350). Instagram Reels / TikTok: 9:16 (1080x1920). Facebook cover: 16:9. Twitter/X header: 3:1. LinkedIn cover: 4:1. Pinterest: 2:3 (1000x1500).

What is the difference between 16:9 and 4:3?

16:9 is widescreen (1.78:1) — standard for modern TVs, YouTube, and most monitors since the late 2000s. 4:3 is near-square (1.33:1) — the old standard for CRT TVs, DVD video, and many tablet screens. A 4:3 video on a 16:9 screen shows black bars on the sides (pillarbox); a 16:9 video on a 4:3 screen shows bars top and bottom (letterbox).

How do I resize an image without distorting it?

Maintain the original aspect ratio by scaling proportionally. This tool calculates the correct height for any target width (or vice versa) so the image is never stretched or squished. To crop to a different ratio, you lose content but avoid distortion. Most editors (Photoshop, GIMP, Lightroom) have a 'constrain proportions' toggle that does this automatically.

What's the aspect ratio of common screens?

Modern TVs and computer monitors: 16:9 (HD standard). Ultrawide monitors: 21:9 or 32:9. Old TVs and some monitors: 4:3 (pre-HD). Smartphones: typically 19.5:9 or 20:9 vertical (significantly taller than 16:9). iPad: 4:3 (closer to traditional document ratio). MacBook: 16:10 (slightly taller than standard 16:9). The trend is more variety in aspect ratios as displays optimize for specific use cases (productivity, gaming, video consumption). When designing across platforms, design for the widest expected ratio and ensure content remains readable when cropped or letterboxed to others.

Why is 16:9 the standard for HD video?

Historical decision in the 1990s as TV transitioned to widescreen. 4:3 was the original standard (matching film's typical ratio at the time). 16:9 was chosen as the HD standard because it (a) accommodated wider movie ratios better (most films are wider than 16:9 but closer than 4:3), (b) gave a more 'cinematic' feel for HDTV vs CRT, (c) was a compromise between various proposed widescreen ratios. By the time HD was standardized in 1996, virtually all consumer displays moved to 16:9. Cinema continues using wider ratios (1.85:1 or 2.39:1) for theatrical releases; home consumption mostly happens at 16:9.

What's the best aspect ratio for social media?

Different per platform. Instagram feed: 1:1 (square) is safe; 4:5 (portrait) takes more screen real estate and gets more engagement. TikTok: 9:16 (full-screen vertical) is the only practical option. YouTube: 16:9 standard. Twitter/X: 16:9 for video; 1.91:1 for images works well. LinkedIn: 1.91:1 horizontal works well. Facebook: 1.91:1 for shared images. Pinterest: 2:3 vertical performs best. The 'meta-rule': vertical content for mobile-first platforms (Instagram Stories/Reels, TikTok, Pinterest); horizontal/landscape for desktop-first platforms (LinkedIn, YouTube, Twitter video).

Can I change aspect ratio without cropping?

Only by adding canvas (letterboxing or pillarboxing). Letterbox: black bars on top and bottom when wide content fits a narrow frame. Pillarbox: black bars on sides when narrow content fits a wide frame. Both preserve the original content but waste display space with black. Cropping is more aesthetically common; letterboxing/pillarboxing is used when the content is critical (movie releases that preserve original aspect ratio over TV's 16:9). Some tools 'extend canvas' by AI-generating new content to fill expanded edges (Photoshop's Generative Expand, similar features in other tools); results are good for landscape backgrounds and bad for complex foreground objects.

How do I find the GCD to simplify a ratio?

GCD (greatest common divisor) is the largest number that divides both inputs evenly. Manual calculation: list factors of each number, find the largest shared. Or use the Euclidean algorithm: GCD(a, b) = GCD(b, a mod b), repeating until b = 0. Example: 1920 and 1080. 1920 mod 1080 = 840. 1080 mod 840 = 240. 840 mod 240 = 120. 240 mod 120 = 0. GCD = 120. So 1920:1080 = (1920/120):(1080/120) = 16:9. The calculator does this automatically; no need to compute by hand.