Aspect Ratio Calculator — Calculate and Convert Image Ratios Free
The Aspect Ratio Calculator is a free online tool with three modes: calculate a ratio from two pixel dimensions, resize dimensions while keeping the ratio locked, or calculate missing dimensions from a known ratio (e.g. 16:9 at 1080p height → 1920 wide). Includes a common ratios reference table, visual preview rectangle, and quick pixel resolution buttons. All calculations are instant and run in your browser.
How to Use the Aspect Ratio Calculator
- 01
Choose a calculation mode
Select from three tabs: calculate a ratio from two dimensions, resize while keeping a ratio locked, or get the missing dimension from a known ratio.
- 02
Enter your values
Type the dimensions or ratio. All calculations update instantly — no need to click a button. The visual preview rectangle updates to show the proportion.
- 03
Copy or use a preset
Copy any result to the clipboard, or click a ratio in the reference table to instantly populate the current tab with that ratio's example dimensions.
Features
- ✓Three calculation modes: ratio, resize, dimensions
- ✓GCD-based ratio simplification (e.g. 1920:1080 → 16:9)
- ✓Decimal ratio output (e.g. 1.7778:1)
- ✓Nearest standard ratio detection
- ✓Resize with ratio lock — type width or height
- ✓Fit within a bounding box calculator
- ✓Dimensions from ratio (e.g. 16:9 at 1080p → 1920×1080)
- ✓Quick resolution buttons: 720p, 1080p, 1440p, 4K
- ✓Visual aspect ratio preview rectangle
- ✓Common ratios reference table (9 ratios)
- ✓Click any ratio to populate inputs
- ✓100% browser-based — no upload, no login
Frequently Asked Questions
What is an aspect ratio?
An aspect ratio is the proportional relationship between an image's width and its height, expressed as two numbers separated by a colon (e.g. 16:9). A 1920×1080 image has an aspect ratio of 16:9 because both dimensions divide evenly by 120, giving 16 and 9. Aspect ratios are used in video production, photography, web design, and display screens.
How do I find the aspect ratio of an image?
Use the "Ratio from dimensions" tab. Enter the width and height of your image in pixels and the tool instantly calculates the simplified ratio (e.g. 16:9), the decimal equivalent (1.7778:1), and identifies the nearest standard ratio.
How do I resize an image without distorting it?
Use the "Resize keeping ratio" tab. Enter the original width and height, then type either the new width or the new height — the other dimension is calculated automatically to maintain the exact proportional relationship. Use the "Fit within a box" feature to find the largest size that fits inside a specific maximum width × height.
What does 16:9 mean in pixels?
16:9 means the width is 16 units for every 9 units of height. Common 16:9 resolutions include 1280×720 (720p), 1920×1080 (1080p/Full HD), 2560×1440 (1440p/QHD), and 3840×2160 (4K/UHD). Use the "Dimensions from ratio" tab and click the resolution quick buttons to see these instantly.
What is the aspect ratio of a standard smartphone screen?
Most modern smartphones use a 9:16 portrait aspect ratio (the inverse of 16:9 widescreen). Some newer phones use taller ratios like 9:19.5 or 9:21. For portrait video and content like TikTok and Instagram Stories, 9:16 is the standard.