Aspect Ratio Calculator
Work out width or height for a target aspect ratio.
What Is This Tool?
This is a small calculator, not an image editor. Enter an aspect ratio and one pixel dimension, and it fills in the other so the proportions match. It can also take a pixel width and height and reduce them to the simplest whole-number ratio using the greatest common divisor.
How It Works
Set the Ratio fields, or pick a preset.
Enter the pixel dimension you know.
Click Solve width or Solve height.
Or enter both pixel values and click Reduce px to ratio.
Everything runs locally in your browser — the image you choose is decoded onto an HTML canvas on your own device and is never uploaded to a server.
Features
- Solve either dimension from a ratio
- Common presets (16:9, 4:3, 1:1, 21:9, 9:16)
- Reduce any pixel size to its simplest ratio
- Results rounded to whole pixels
- No image upload — pure maths
Common Use Cases
- Finding the height for a 1600px-wide 16:9 banner
- Checking whether an image is already 4:3
- Planning crop dimensions before editing
- Matching a video thumbnail to the video’s ratio
Frequently Asked Questions
Why is the result not a whole number sometimes?
It is rounded to the nearest whole pixel. A 1000px width at 16:9 is 562.5px tall, shown as 563 — expect a one-pixel difference in edge cases.
What does "reduce px to ratio" do?
It divides your width and height by their greatest common divisor. So 1920×1080 reduces to 16:9, and 1024×768 reduces to 4:3.
Does this resize my image?
No. It only calculates numbers. Use the Image Resizer to actually change an image.
Can I use it for video?
Yes. Aspect ratio maths is the same for images and video frames.
Is any data sent anywhere?
No, the calculation runs in your browser.