ToolBirch

Aspect Ratio Calculator

Find a ratio and compute the matching dimensions for a resize.Calculators

Aspect Ratio Calculator

Get the aspect ratio of a size and compute the matching dimensions when one side changes.

Aspect ratio
16:9
As decimal
1.7778
Matching size
1280 × 720
rounded to whole pixels

About this tool

Enter an original size, change one side, and get the other side back without stretching anything. The ratio simplifies to whole numbers such as 16:9, and the decimal form is shown for video and sensor work.

How to use the Aspect Ratio Calculator tool

  1. Enter the original size. Width and height in pixels — or any unit, the maths is the same.
  2. Enter the new dimension. Choose whether the known new value is the width or the height.
  3. Read the results. The simplified ratio, its decimal form, and the matching new dimensions.

Supported formats

Input

  • Original width and height
  • One new dimension

Output

  • Simplified ratio
  • Ratio as a decimal
  • Matching dimensions

Inputs are validated before anything is processed. Invalid values and unsupported files are rejected with a clear error instead of failing silently.

Frequently asked questions

How is the ratio simplified?

By dividing both sides by their greatest common divisor, so 1920×1080 becomes 16:9 exactly.

What is decimal mode for?

Some sizes do not reduce cleanly. The decimal form shows the true ratio, useful for camera sensors and video standards.

Are the new dimensions rounded?

Yes, to whole pixels, which is what image tools expect. A one-pixel difference from the exact value is possible.

Can I use units other than pixels?

Yes. The ratio is unitless, so centimetres, inches or any consistent unit works.

Privacy

Everything you enter stays in this browser tab. There is no upload endpoint for tool inputs, no account, and no server-side copy of your text or files. Results are produced locally and disappear when you close the page.

No account is required and no file is ever uploaded. See the privacy policy for details about analytics and the limited data this site stores.

Known limitations

  • Ratio simplification uses integer arithmetic; tiny rounding in the input can change the simplified form.
  • Decimal simplification mode approximates to the nearest clean ratio rather than proving one.
  • Only one resize target can be computed at a time.

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