Aspect Ratio Calculator: Resize Images While Keeping Proportions

Resizing an image or video without distortion means maintaining its aspect ratio — the proportional relationship between width and height. Whether you are preparing images for a website, setting up a video export, or designing for multiple screen sizes, getting the aspect ratio right prevents stretching, cropping surprises, and layout issues.

What is an Aspect Ratio?

An aspect ratio expresses the relationship between width and height as two numbers separated by a colon. A 16:9 ratio means for every 16 units of width, there are 9 units of height.

1920 x 1080 pixels
1920 / 1080 = 1.778
GCD(1920, 1080) = 120
1920 / 120 : 1080 / 120 = 16:9

The ratio describes the shape, not the size. A 1920x1080 display and a 3840x2160 display are both 16:9 — one is just larger.

Common Aspect Ratios

Ratio	Decimal	Common Uses
1:1	1.0	Instagram posts, profile pictures, album art
4:3	1.333	Classic TV, iPad display, PowerPoint slides
3:2	1.5	DSLR photos, MacBook displays, 35mm film
16:9	1.778	YouTube, HDTV, most monitors, presentations
16:10	1.6	MacBook Pro, some desktop monitors
21:9	2.333	Ultrawide monitors, cinematic video
9:16	0.5625	Vertical video (TikTok, Reels, Stories)
2:3	0.667	Portrait photos, Pinterest pins
4:5	0.8	Instagram portrait posts

How to Use Our Aspect Ratio Calculator

Calculate the Ratio from Dimensions

1. Enter the width and height of your image or video
2. See the simplified ratio displayed instantly (e.g., 1920x1080 shows as 16:9)
3. View the decimal value for precise comparison

Resize While Maintaining Ratio

1. Enter the original dimensions (or enter a known ratio)
2. Change either the width or height to your desired new value
3. The other dimension auto-calculates to maintain the exact ratio
4. No stretching, no distortion

Tips

• Lock the ratio first, then adjust one dimension — the calculator handles the math
• Use the common ratios reference to quickly select a standard format
• The calculator shows the greatest common divisor (GCD) reduction for clean ratio numbers
• Works with any unit: pixels, inches, centimeters, or abstract units

Platform Dimension Guide

Social Media Images

Platform	Format	Dimensions	Ratio
Instagram	Square post	1080 x 1080	1:1
Instagram	Portrait post	1080 x 1350	4:5
Instagram	Story/Reel	1080 x 1920	9:16
Facebook	Shared image	1200 x 630	40:21
Twitter/X	In-stream image	1600 x 900	16:9
LinkedIn	Shared image	1200 x 627	~1.91:1
Pinterest	Standard pin	1000 x 1500	2:3
YouTube	Thumbnail	1280 x 720	16:9
TikTok	Video	1080 x 1920	9:16

Video Resolutions

Name	Dimensions	Ratio
720p (HD)	1280 x 720	16:9
1080p (Full HD)	1920 x 1080	16:9
1440p (2K)	2560 x 1440	16:9
2160p (4K UHD)	3840 x 2160	16:9
4K Cinema	4096 x 2160	~1.9:1
Ultrawide 1080p	2560 x 1080	21:9

Practical Use Cases

Responsive Web Design

You have a hero image at 1920x800 and need versions for tablet (1024px wide) and mobile (640px wide). Enter the original dimensions, then change the width to 1024 — the calculator gives you a height of 427. Change to 640 — you get 267. Every version maintains the same proportions.

Video Editing

Your footage is 4K (3840x2160 at 16:9) but you need a vertical cut for social media at 9:16. Enter 1080 width and switch to the 9:16 ratio — your export should be 1080x1920. Knowing this upfront helps you frame shots correctly during editing.

Print and Photography

A client wants a 24x36 inch poster from a photo that is 6000x4000 pixels (3:2 ratio). Check: 24x36 is also 2:3 (portrait orientation of 3:2). The photo fits perfectly without cropping. If they wanted 24x30, the ratio would be 4:5 — you would need to crop the photo.

UI Component Design

Designing card components for a grid layout, you want all thumbnails to share the same ratio. Setting cards to 16:9 means a 320px-wide card needs a 180px-tall image area. Consistent ratios across a grid prevent visual unevenness.

Monitor and Display Selection

Comparing monitors: a 27-inch 16:9 display versus a 34-inch 21:9 ultrawide. The aspect ratio tells you about the shape of your workspace. The ultrawide gives significantly more horizontal space, which benefits side-by-side workflows.

The Math Behind Aspect Ratios

Finding the Ratio

To reduce dimensions to their simplest ratio, divide both values by their greatest common divisor (GCD):

Dimensions: 1920 x 1080
GCD(1920, 1080) = 120
Ratio: 1920/120 : 1080/120 = 16:9

Scaling to a New Width

To resize proportionally when you know the target width:

New height = Original height * (New width / Original width)

Original: 1920 x 1080
New width: 1280
New height: 1080 * (1280 / 1920) = 720
Result: 1280 x 720

Scaling to a New Height

Same principle in reverse:

New width = Original width * (New height / Original height)

Original: 1920 x 1080
New height: 600
New width: 1920 * (600 / 1080) = 1066.67 ≈ 1067
Result: 1067 x 600

Frequently Asked Questions

What happens if my image does not match a standard ratio? Not all images fit neatly into standard ratios. A 1200x800 image is 3:2, but a 1200x850 image is 24:17. Non-standard ratios work fine — they just may require letterboxing or cropping to fit standard containers.

Should I crop to a standard ratio? It depends on the platform. YouTube requires 16:9 for optimal display. Instagram prefers 1:1 or 4:5. For your own website, you can use any ratio that suits your design, as long as you are consistent across similar elements.

Does aspect ratio affect file size? Aspect ratio itself does not affect file size — total pixel count does. A 1920x1080 image (2.07 megapixels) and a 1080x1920 image (also 2.07 megapixels) have the same pixel count and similar file sizes despite different orientations.

How do I handle retina/HiDP displays? For retina displays, export images at 2x the CSS dimensions. If your layout shows an image at 400x300 CSS pixels, export it at 800x600 actual pixels. The aspect ratio stays the same — only the total pixel count doubles (or triples for 3x).

What is the difference between DAR and PAR? Display Aspect Ratio (DAR) is what you see on screen. Pixel Aspect Ratio (PAR) describes the shape of individual pixels. Most modern displays use square pixels (PAR 1:1), so DAR matches the pixel dimensions directly. Some older video formats use non-square pixels.

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Try our free Aspect Ratio Calculator to resize images while maintaining perfect proportions instantly.