Aspect ratio and resize calculator
Find a proportional width/height for an image.
Your inputs
Your results
Ready when you areYour results will appear here.
How it works
Reduce an integer width/height pair to an exact ratio and calculate a proportionally scaled output with one chosen target dimension, rounding to whole pixels.
Read the source reference ↗A few things to know
Whole-pixel rounding introduces a small ratio error. Calculations do not crop, edit or improve image quality. Enlarging an image does not add source detail.
When to use this tool
Calculate a proportional resize before changing the actual file. A chosen width determines the height from the source ratio, subject to pixel rounding.
- Plan an image resize.
- Calculate a thumbnail height.
- Find a reduced aspect ratio.
How to use aspect ratio and resize calculator
Prepare the inputs
Enter the quantities and units used by your source.
Choose the settings
Choose the assumptions and compare them with your actual situation.
Review and export
Review the result, then download the calculation report.
Try the supplied example
Inputs
width: 1920; height: 1080; target: 800; axis: Width
Result
1920 × 1080 reduces to 16:9; choosing width 800 gives 800 × 450.
What it means
Use the image resizer when you need an actual downloadable file.
Common mistakes to avoid
Rounding changes some ratios slightly
Rounding changes some ratios slightly.
Enlargement does not add original detail
Enlargement does not add original detail.
Frequently asked questions
Definitions, edge cases, and practical next steps for this tool. Search all tool FAQs ↗
Does this resize my file?
No. It calculates dimensions.
What is a reduced ratio?
The integer width and height divided by their greatest common divisor.
Can I set height instead?
Yes. Choose Height as the controlling target dimension.
Why can the ratio error be nonzero?
The other dimension must be rounded to a whole pixel.
Does enlargement improve quality?
No. It adds sampled pixels without creating original detail.
Is cropping supported?
Use the separate cropper when the output ratio must differ.
Are my inputs uploaded or stored?
Processing happens locally in your browser. This tool does not upload inputs. Downloads stay on your device; sharing or opening them in another service is your choice.
What should I check before using the output?
Whole-pixel rounding introduces a small ratio error. Calculations do not crop, edit or improve image quality. Enlarging an image does not add source detail.
Explore the topic in the blog
Sources and method
Use the references below to check definitions and platform guidance. The model’s scope and limits are explained above. Read our editorial standards.