Aspect Ratio Calculator

Calculate aspect ratios and new sizes

This aspect ratio calculator reduces any width and height to a simple ratio, like 1920 × 1080 to 16:9. It can also resize dimensions without distortion and fit a size into a maximum box. It works for images, video, screens and web layouts.

How to use it

1. Choose a mode: Find Ratio, Scale Dimensions or Fit in Box.
2. Enter your width and height, or click a preset such as 16:9 or 4:5.
3. Fill in the extra fields for the mode you picked.
4. Click the button to see the result.

The three modes

Mode	You enter	You get
Find Ratio	Width and height	Simplified ratio, decimal ratio and height as a percent of width
Scale Dimensions	Original size, which side to lock, and the new value for that side	New width, new height and scale percent
Fit in Box	Original size and a maximum width and height	The largest size that fits, the scale percent and a CSS padding-top value

How it works

Find Ratio divides both numbers by their greatest common divisor. For 1920 and 1080 that divisor is 120, which gives 16:9. The decimal is width ÷ height, so 16:9 shows 1.7778.

Scale Dimensions keeps width ÷ height the same. If you lock the width and enter 1280 for a 1920 × 1080 image, the new height is 720 and the scale is 66.7%.

Fit in Box first matches the box width. If the height then goes over the box, it matches the box height instead. The whole image stays inside the box, like object-fit: contain. A box larger than the original will scale it up.

The presets fill in sizes such as 1600 × 900 for 16:9 or 400 × 500 for 4:5. Edit them to suit your needs.

Tips

• Results show two decimals. Round to whole pixels before you use them in an image editor.
• Whole numbers give the cleanest ratio. Decimal sizes can produce a ratio like 1.5:1.
• The height percent is the classic CSS padding-top trick for responsive boxes. Modern CSS can also use aspect-ratio: 16 / 9.

Frequently asked questions

What is the aspect ratio of 1920 × 1080?

It is 16:9, the standard widescreen ratio used by most monitors, TVs and online video.

Why does 1366 × 768 not show 16:9?

The calculator gives the exact ratio, which is 683:384. It is close to 16:9, but not exactly the same.

Can I use it for portrait sizes?

Yes. Enter the width first and the height second, or use the 9:16, 2:3 and 4:5 presets for vertical formats.