What Is an Aspect Ratio? Common Image Ratios Explained

How to Calculate an Aspect Ratio

Divide the width and height by their greatest common divisor:

• 1920 × 1080 → both divisible by 120 → 16:9
• 1080 × 1080 → 1:1
• 6000 × 4000 → both divisible by 2000 → 3:2
• 4032 × 3024 → both divisible by 1008 → 4:3

You can also express it as a single number by dividing width by height: 16:9 is about 1.78, 4:3 is about 1.33, 3:2 is 1.5, and 1:1 is 1.0. That decimal form is handy for comparing ratios quickly.

Finding the Missing Dimension

If you know the ratio and one side, the other follows:

height = width × (ratio height ÷ ratio width)
16:9 at 1600 px wide → 1600 × 9 ÷ 16 = 900 px tall
4:5 at 1080 px wide  → 1080 × 5 ÷ 4  = 1350 px tall

Common Image Aspect Ratios

Where 4:3 and 3:2 Come From

Camera sensors set the "native" ratio of your photos. Most phone cameras capture 4:3 by default, while most DSLR and mirrorless cameras capture 3:2, the shape inherited from 35 mm film. That's why phone photos often need cropping to fit 16:9 screens or 3:2 prints.

Aspect Ratio vs Resolution vs File Size

These three are often confused:

• Aspect ratio is the shape (16:9).
• Resolution is the number of pixels (1920 × 1080).
• File size is how much storage the image takes (for example 450 KB), which also depends on format and compression.

Changing one doesn't fix the others. Resizing a 4:3 image to a different pixel size keeps it 4:3. Cropping changes the ratio but also reduces resolution, because pixels outside the crop are removed. How to crop an image without losing quality explains how to keep as much resolution as possible.

Orientation: Landscape, Portrait and Square

The order of the numbers tells you the orientation. By convention the width comes first:

• Landscape ratios have the larger number first (16:9, 4:3, 3:2).
• Portrait ratios have the smaller number first (9:16, 3:4, 2:3).
• Square is 1:1.

The same shape rotated swaps the numbers, so 4:3 and 3:4 are the same rectangle turned on its side. When a platform asks for "4:5", it means a portrait image slightly taller than it is wide.

Ratios That Aren't Whole Numbers

Some ratios are traditionally written with decimals because the shapes come from film or paper standards rather than neat fractions:

• 1.85:1 and 2.39:1 are common cinema ratios, both wider than 16:9.
• 1.91:1 is a landscape ratio used for link previews on several social platforms.
• A-series paper (A4, A3) has a ratio of 1:√2, about 1:1.414, chosen so that cutting a sheet in half produces the same shape at the next size down.

You can convert any of these to the "W:H" style by multiplying both numbers until they're whole, but the decimal form is usually clearer.

Changing an Image's Aspect Ratio

There are three ways to fit an image into a new ratio:

1. Crop: remove part of the image. The result fills the frame with no bars, but you lose the edges.
2. Pad (letterbox or pillarbox): add bars or a background around the image. Nothing is lost, but the frame has empty areas.
3. Stretch: force it into the new shape. Avoid this; people and circles look visibly distorted.

Cropping is usually the best choice for photos. The image cropper locks the crop box to an exact ratio (4:3, 3:4, 16:9, 9:16, 3:2 or 1:1) so you only need to choose what to keep, then lets you set the output size and download as JPG, PNG or WebP. It runs in your browser, so the photo isn't uploaded.

Choosing the Right Ratio

• For a screen, match the screen: 16:9 for TVs, laptops and YouTube; 9:16 for phone-first vertical video. How to crop an image to 16:9 and cropping for stories and Reels cover those cases.
• For print, match the paper size, since prints come in fixed shapes. How to crop photos for printing lists common print ratios.
• For a social post, follow the platform's current guidance. Platforms change their preferred shapes from time to time; for example, Instagram's profile grid moved to taller 3:4 previews in 2025.
• When unsure, crop to the destination's ratio yourself. Automatic cropping by apps tends to cut off heads and text.

Summary

An aspect ratio is width compared to height, independent of pixel count. Learn the handful of common ratios, match the destination, and crop rather than stretch when you need to change shape.