Jernej LeticaPhotography Tools & Stories
Image Tools

Find a ratio or a missing side

Find the simplest width-to-height ratio, or calculate a missing dimension as you type.

Built and written by Jernej Letica

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Dimensions to ratio
Ratio to dimensions

How to calculate an aspect ratio

  1. Enter the original width and height in the first pair of fields.
  2. Read the reduced ratio immediately beneath the dimensions.
  3. To find a missing side, pick a ratio, enter the known dimension and choose whether it is width or height.

Why I check the shape first

I decide on a photograph’s shape before I resize it. A wide frame and a portrait frame tell different stories, even when they contain the same number of pixels. This calculator lets me separate that choice from the size of the exported file.

What I checked in the browser

I entered 1920 × 1080 and got 16:9. With 4:5 selected and a known width of 1080, the missing height was 1350 pixels. Those are calculations on the entered dimensions; the tool does not crop or stretch a photograph.

Ratio and resolution answer different questions

A ratio describes the relationship between the sides. Resolution gives their actual pixel counts. Both 1920 × 1080 and 3840 × 2160 are 16:9, but the second has four times as many pixels. Use whole pixel dimensions when simplifying an existing image.

A missing side may need rounding

The ratio fields accept decimal values for less common formats. The missing dimension is shown to two decimal places when necessary. Real image files need whole pixels, so round the result before entering it into a resizer. A one-pixel rounding difference is usually smaller than the crop needed to match an unusual frame.

Tips for better results

  • Keep width first and height second; reversing them makes a portrait ratio.
  • Use 4:5 for an upright rectangle and 9:16 for a much taller one.
  • Check whether a publishing specification asks for a ratio or an exact pixel size.

Privacy

Your file or entered content never leaves your device. The calculations and downloads happen locally in your browser.

Frequently asked questions

Does this change my image?

No. The calculator works only with the dimensions you enter. It does not open or edit a picture. After choosing the shape, use the cropper for a different composition or the resizer for a different pixel count.

Why does 1920 by 1080 become 16:9?

Both dimensions divide exactly by 120. Dividing them by that common factor gives 16 and 9, the smallest pair of whole numbers that describes the same shape.

Can I enter a decimal ratio?

Yes. Enter the width and height components separately. A decimal ratio can produce a fractional missing side; an image editor will require you to round that result to a whole number of pixels.

Which side is calculated?

Choose the dimension you already know in Known dimension. If you select Width, the result is the required height. If you select Height, the calculator returns the required width.

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