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Original dimensions and one desired output dimension.
Quick math
Aspect ratio calculator
Resize media proportionally and reduce dimensions to a simple ratio.
Privacy built inYour work stays with you
Common ratios
Simplified ratio
16:9
Decimal ratio
1.7778
Matching dimensions
1,280 × 720
Same aspect ratio
CSS aspect-ratio
1920 / 1080
Preview
Your work stays private in your browser while you use this tool.
What does aspect ratio calculator do?
The aspect-ratio calculator reduces a positive width and height to a ratio, reports the decimal width-to-height value, and calculates the matching height for a target width.
- Input
- Original dimensions and one desired output dimension.
- Result
- Simplified ratio and matching output size.
- Price
- Free
- Account
- Not required
How to use aspect ratio calculator
Choose your settings
Resize media proportionally and reduce dimensions to a simple ratio.
Save or copy
Simplified ratio and matching output size.
A practical tip
Round only at the end to avoid accumulating sizing errors.
When to use aspect ratio calculator
Resize a 1920×1080 video frame to a 1280-pixel-wide export without distortion.
Identify whether supplied artwork is 16:9, 4:3, square, or another ratio.
Calculate a proportional CSS placeholder height before an image loads.
Worked example
A concrete aspect ratio calculator example
- Input
- 1920 × 1080
- Settings
- Target width: 1280
- Result
- Simplified ratio: 16:9; decimal ratio: 1.7778; matching dimensions: 1280 × 720.
What to expect
How it works
The displayed ratio finds a greatest common divisor from the source dimensions rounded to integers, then divides the entered width and height by that divisor. The decimal ratio is width divided by height, and a new height is calculated as target width × source height ÷ source width.
Know before using
Limits and edge cases
- The simplified ratio uses dimensions rounded to integers, so fractional source dimensions can yield a ratio that does not exactly describe the original decimals.
- The resizer solves from a target width only; it does not crop, inspect an image file, or calculate from a target height.
Standards and sources
Common questions
Aspect ratio calculator FAQ
Is aspect ratio calculator free to use?
Yes. Aspect ratio calculator is free to use.
Does aspect ratio calculator keep my work private?
Yes. Your work stays private while you use the tool — nothing you enter is uploaded.
Does matching the ratio guarantee the same image quality?
No. Aspect ratio describes shape, not resolution, compression, or sharpness. A 160×90 image and a 3840×2160 image are both 16:9.
Why must width and height be greater than zero?
A zero or negative dimension cannot describe a usable rectangular frame or produce a finite width-to-height ratio.