How do you calculate aspect ratio?

Divide width and height by their greatest common divisor. For example, 1920 by 1080 simplifies to 16:9.

How do you calculate missing height from aspect ratio?

Use height = width × ratio height ÷ ratio width. For a 16:9 ratio and 1280px width, height is 1280 × 9 ÷ 16 = 720px.

How do you calculate missing width from aspect ratio?

Use width = height × ratio width ÷ ratio height. For a 16:9 ratio and 720px height, width is 720 × 16 ÷ 9 = 1280px.

Does this aspect ratio calculator need a backend?

Calculations are handled in the browser for this tool based on the current public implementation.

Free browser tool

Aspect Ratio Calculator for Images & Video

Calculate missing dimensions, simplify width and height into a ratio, and scale image or video sizes for common formats like 16:9, 4:3, 1:1, and 9:16.

Aspect ratio inputs

Calculate a missing dimension or simplify an existing width and height.

Target ratio

Known width

Result

Rounded to two decimals for display; calculations keep full precision.

Calculated dimensions

1,920 × 1,080

Ratio

16:9

Decimal

1.78

Orientation

Landscape

Common widths at 16:9

320px × 180px

640px × 360px

1280px × 720px

1920px × 1,080px

Dimension results are math helpers. Round final exports according to your image editor, video encoder, or platform upload requirements.

Quick answer

An aspect ratio calculator keeps image or video dimensions proportional when one side changes.

For 16:9, 1920px wide becomes 1080px high; for 9:16, 1080px wide becomes 1920px high.

Best inputs for resize planning

Use the final platform ratio

Choose 16:9 for widescreen, 1:1 for square thumbnails, 4:5 for portrait cards, and 9:16 for vertical stories.

Round carefully

Pixel dimensions may need rounding, so check platform minimum sizes before exporting images or videos.

Aspect ratio formulas

Use these formulas to audit the result manually.

height = width × ratio height ÷ ratio width

width = height × ratio width ÷ ratio height

ratio = width ÷ height, then simplify with GCD

Common ratios

16:9 is common for widescreen video and thumbnails. 1:1 is common for square posts. 9:16 is common for vertical video. 3:2 and 4:3 are common in photography and presentations.

The calculator focuses on dimensions and ratios only; use a dedicated image tool when you need to edit or export a file.

Example, assumptions, and limitations

Use this calculator to plan dimensions before resizing, cropping, or exporting media.

Example

A 16:9 image at 1280px wide should be 720px high because 1280 x 9 / 16 = 720.

Assumption

The calculation preserves geometric proportions. It does not inspect image content or decide crop positioning.

Limitation

Rounded pixel dimensions can create a tiny ratio difference. Platform-safe areas and compression rules are not included.

Common use cases

Use ratio math before cropping, resizing, uploading, or designing fixed media slots.

Image resize planning

Calculate missing width or height before resizing a JPG, PNG, or WEBP image.

Video thumbnails

Plan 16:9, 9:16, or 1:1 dimensions for video covers and social previews.

Design handoff specs

Translate aspect ratios into exact pixel dimensions for product cards and content slots.

Crop preparation

Pick target dimensions before using the image cropper for square, portrait, or widescreen crops.

Frequently asked questions

What size is 16:9 at 1920px wide?

At 1920px wide, a 16:9 image or video is 1080px high because 1920 × 9 ÷ 16 = 1080.

What aspect ratio is 1080 by 1920?

1080 by 1920 simplifies to 9:16, which is a common vertical video format.

Can I use this before cropping an image?

Yes. Use the calculator to decide the target dimensions, then crop the file with the Image Crop Tool.

How is image sizing processed?

No. This page only calculates dimensions and ratios in the browser. It is designed for browser-side processing based on the current public implementation.

Suggested workflow