Resize images in your browser

What this tool does

The tool scales pictures to a new width and height in pixels and writes them in their original format. It offers four methods: a percentage of the original size, a width or height that the picture must fit while keeping its proportions, an exact width and height, and a print size in centimetres or inches at a resolution in DPI.

For an exact or print size, a picture with other proportions is either fitted without cropping, with borders in a colour you choose, or stretched. Several pictures can be resized in one run.

How to use it

1. Choose the pictures, or drop them on the marked area.
2. Choose the method under Resize by.
3. Enter the percentage, the width and height in pixels, or the printed width and height with the unit and the resolution.
4. For an exact or print size, choose what happens if the proportions differ: Fit without cropping (with a border colour) or Stretch to fill.
5. Start. The list shows the old and the new pixel size of every file.
6. Download single files from the list, or all of them as one ZIP archive.

How the new size is calculated

• Percentage: width and height are both multiplied by the percentage divided by 100. Values from 1 to 400 are accepted.
• Width or height, keeping proportions: the picture is scaled by the largest factor with which it still fits the values you entered. If you enter only a width, the height follows from the proportions, and the other way round.
• Exact width and height: the result has exactly that size. With Fit without cropping, the picture is scaled as large as fits and centred, and the rest becomes a border; with Stretch to fill, it is drawn into the whole size and looks stretched or squeezed if the proportions differ.
• Print size: pixels = inches × DPI, and 1 inch is exactly 2.54 cm. 15 cm at 300 DPI are 15 ÷ 2.54 × 300 = 1771.7, rounded to 1772 pixels. With one side given, the other follows the proportions of the picture; with both, the choice for different proportions applies as for an exact size.

Results are rounded to whole pixels, and no side becomes smaller than 1 pixel. With the second method, smaller pictures keep their size unless you choose to enlarge them.

With a print size, the resolution is also written into the file: into the JFIF header of a JPG (JFIF 1.02, dots per inch) and into the pHYs chunk of a PNG (pixels per metre: 300 DPI are 300 ÷ 0.0254 = 11,811). Programs that print or place the picture then use that size. WebP has no such field, so a WebP has the right pixels but its print size must be set when printing.

JPG and WebP results are written with quality 90, PNG results without loss. As in all image tools, only the pixels are written; metadata of the original is not copied.

Worked example

A photo has 4032 × 3024 pixels. A website accepts pictures of at most 1200 pixels on each side.

Choose the second method and enter 1200 for the width and 1200 for the height. The factor for the width is 1200 ÷ 4032 ≈ 0.298, the factor for the height is 1200 ÷ 3024 ≈ 0.397. The smaller one is used, so the picture fits both limits: the result is 1200 × 900 pixels.

A portrait photo of 3024 × 4032 pixels in the same run becomes 900 × 1200 pixels. With the percentage method and 50, the first photo becomes 2016 × 1512 pixels, which is a quarter of the pixels.

For prints, two camera photos were resized in Chrome to 6 × 4 inches at 300 DPI, which is 1800 × 1200 pixels. The landscape photo of 4288 × 2848 pixels has almost the same proportions: it became 1800 × 1196 pixels with a white border of 2 pixels above and below, 308,485 bytes, with 300 DPI recorded in the file. The portrait photo of 1668 × 2500 pixels fits a landscape 6 × 4 badly and got wide borders at the sides; as 10 × 15 cm (1181 × 1772 pixels) it filled the size almost exactly.

The same portrait photo as an exact size of 1080 × 1080 pixels, for a square post without cropping: the photo became 721 × 1080 pixels (1668 × 1080 ÷ 2500 = 720.6, rounded), with borders of 179 and 180 pixels at the sides.

Common mistakes

• Enlarging a small picture and expecting more detail. The picture gets more pixels but no new information, so it looks soft.
• Choosing Stretch to fill for pictures with other proportions. Faces and circles get distorted; choose Fit without cropping, or crop to the wanted proportions first.
• Choosing a landscape print size for a portrait photo. 6 × 4 inches is landscape; for an upright photo enter 4 × 6.
• Expecting a higher DPI value alone to improve a print. The resolution only says how large the pixels are printed; a small picture printed large stays soft.
• Confusing pixel size and file size. To get below a number of bytes, use the compress tool, which can also reduce the longest side.
• Resizing a JPG several times in a row. Each run writes the picture again with loss. Start from the original each time.