Aspect Ratio Calculator

Aspect Ratio Calculator: Resize Without Stretching

An aspect ratio is the relationship between the width and height of a screen, image, or video. A 16:9 ratio, for example, means that for every 16 units of width there are 9 units of height.

Get the ratio wrong and your content looks stretched, squashed, or cropped. This aspect ratio calculator helps you pick a ratio, set your width and height, and see the shape of the result right on the page.

What This Tool Lets You Do

The calculator has four main parts:

• Common Presets: a dropdown with popular ratios, so you don’t need to type anything for standard sizes.
• Width (ratio) and Height (ratio): the two numbers that define the ratio, such as 16 and 9.
• Width (pixels) and Height (pixels): the actual size of your image, video, or canvas, such as 1280 × 720.
• Live Shape Visualizer: a preview box that shows what your ratio looks like, labeled with the ratio itself (for example, 16:9).

The visualizer is useful because numbers alone can be hard to picture. A quick look tells you whether your shape is wide, tall, or square.

How to Use the Aspect Ratio Calculator

1. Choose a preset from the “Common Presets” dropdown if your target is a standard format. The ratio and pixel fields show the matching values (the default is HD Video 16:9 at 1280 × 720).
2. Or select “Custom Dimensions…” to enter your own ratio and pixel values.
3. Check the Live Shape Visualizer to confirm the proportions look the way you expect.
4. Use the pixel width and height in your design software, video editor, or website code.

Built-In Presets and When to Use Them

Preset	Ratio	Typical use
HD Video	16:9	YouTube videos, presentations, most TVs and laptop screens
Instagram Square	1:1	Square social posts, profile images, thumbnails
Standard Monitor	4:3	Older monitors and TVs, some tablets, slide decks, classic photo prints
Mobile Story/Reel	9:16	Vertical, full-screen phone video such as Stories and Reels
Ultrawide	21:9	Ultrawide monitors and cinematic-style video

Platforms update their recommended sizes from time to time. For important uploads, check the platform’s current guidelines too.

How Aspect Ratio Math Works

You can do this by hand. The calculator saves you the effort and the mistakes.

Finding a missing height:
Height = Width × (Ratio Height ÷ Ratio Width)

Example: you need a 16:9 image that is 1280 pixels wide.
1280 × (9 ÷ 16) = 720 pixels high.

Finding a missing width:
Width = Height × (Ratio Width ÷ Ratio Height)

Example: you need a 9:16 vertical video that is 1920 pixels tall.
1920 × (9 ÷ 16) = 1080 pixels wide.

Finding the ratio from a size:
Divide both numbers by their greatest common divisor. For 1920 × 1080, both divide by 120, which gives 16:9.

Common Sizes by Ratio

These are widely used pixel sizes that match each ratio:

• 16:9: 1280 × 720, 1920 × 1080, 3840 × 2160
• 1:1: 1080 × 1080
• 4:3: 1024 × 768, 1600 × 1200
• 9:16: 1080 × 1920
• 21:9: 2560 × 1080 is commonly sold as “21:9”, though its exact ratio is closer to 64:27. Marketing labels are often rounded.

Practical Tips

• Match the ratio before you resize. Set the ratio first, then adjust the pixel size. Changing only one dimension without keeping the ratio is what causes stretching.
• Crop instead of stretching. If your source image has a different ratio than your target, crop it to the new shape. Do not force it to fit.
• Plan for several formats. If one video will go on YouTube (16:9) and Reels (9:16), keep important content near the center so it survives both crops.
• Use the visualizer as a quick check. If the shape looks wrong, your ratio values probably have a typo, such as 19:6 instead of 16:9.
• Prefer even numbers for video. Many video encoders work best with even pixel dimensions.

Who Can Use This Tool

• Video creators setting export sizes for different platforms
• Designers building banners, thumbnails, and social graphics
• Web developers reserving space for responsive images and embeds
• Photographers planning crops for prints or frames
• Gamers and monitor shoppers comparing 16:9, 4:3, and ultrawide screens

Frequently Asked Questions

What is an aspect ratio?

It is the proportional relationship between width and height, written as two numbers separated by a colon, like 16:9. It describes shape, not actual size. A 16:9 image can be 640 pixels wide or 4,000 pixels wide.

What is the difference between aspect ratio and resolution?

Resolution is the exact pixel count, such as 1920 × 1080. Aspect ratio is the simplified shape of that size, which is 16:9 in this case. Many different resolutions can share one aspect ratio.

Which aspect ratio should I use for YouTube?

16:9 is the standard for regular YouTube videos. Vertical formats like 9:16 are used for Shorts.

What ratio is best for vertical phone video?

9:16 fills a phone screen held upright. It is the ratio behind the “Mobile Story/Reel” preset.

Can I enter a ratio that isn’t in the presets?

Yes. Choose “Custom Dimensions…” and enter your own ratio and pixel values.

Why does my image look stretched after resizing?

Usually the new width and height don’t follow the original ratio. Keep the ratio the same, or crop the image to the new shape.

Is 21:9 exactly 21 to 9?

Often not. Many “21:9” ultrawide screens use resolutions like 2560 × 1080, which is about 2.37:1. The label is a rounded, commonly used name.