Resolution Scaler

How it is calculated

To keep the proportions the tool uses new_height = orig_height × new_width / orig_width. Width and height are in pixels. The ratio shown is the original width and height divided by their greatest common divisor, found with Euclid's algorithm after rounding both to whole numbers.

The new height is given to two decimals and is not rounded to a whole pixel, so a result such as 449.78 px must be rounded by you (to 450) before you use it, and the picture will then be a tiny fraction off the exact ratio. You can only set a new width; to scale from a height, swap the two original values and enter the target height as the width. The original width and height must be greater than zero. Sizes that share no common factor stay unreduced, for example 1000×667 shows as 1000:667.

Common mistakes

• Typing the new height in the new-width box. The tool always takes the new width and works out the height.
• Using the result without rounding. A height like 449.78 px is not a real pixel size; round to a whole number, accepting a tiny change in ratio.
• Expecting a clean ratio from a size such as 1366×768. It reduces to 683:384, not 16:9, because the screen is only close to 16:9.
• Entering the width and height in inches or centimetres and expecting pixels. The proportion works in any unit, but the label says px.
• Swapping original width and height, which makes a landscape image come out as portrait.