Image Resizer – Resize by Pixels or Percent

Resize an image by pixels or percentage

Use exact pixels when an upload form, website or email needs a particular width and height. Choose percentage when you simply want the image to be smaller or larger than the original: 50% halves both dimensions, while 200% doubles them. The result panel reports the actual output dimensions and file size before download.

Resize an image in centimetres, millimetres or inches

Choose Print size (cm, mm or inches), pick the unit and type the width and height. DPI presets are 72, 96, 150 and 300, or type a custom value. The control shows the pixel size before you run it. JPG and PNG downloads store that DPI. WebP does not, because DPI is metadata and the pixel size is what the image contains. A higher DPI does not add detail the original never had.

Resize an image to exact pixels

Add a JPG, PNG or WebP file, keep Exact width and height selected, then type the required pixel dimensions. Keep Keep aspect ratio selected when you want the image to retain its original proportions. Changing either width or height updates the other value automatically so photographs, logos and screenshots do not become stretched.

Scale an image by percentage

Select Percentage of original and enter a value from 1% to 400%. Percentage resizing always keeps the original proportions. Values below 100% reduce the dimensions and usually the file size. Values above 100% enlarge the canvas, but cannot recreate detail that was not captured in the source image.

Resize versus crop

Resizing changes an image’s pixel dimensions without removing any part of it. If a destination needs a different shape without stretching, use the image crop tool first to choose the area that fits, then resize the cropped result. For ready-made Instagram, Facebook, X, LinkedIn and YouTube dimensions, use the existing social media image resizer. That resizer can crop to fill a frame or fit the whole image on a background colour. This page keeps every pixel of the picture: with the aspect lock on it does not stretch, and it does not add bars.

Resize versus compress

Resizing can reduce file size when it removes pixels, but it does not target a specific KB value. If a destination has a file-size limit, resize to the smallest dimensions it needs, then use the image size reducer to target a JPG or WebP size in KB. Keep the original image as a master copy instead of repeatedly changing the same downloaded file.

Private image resizing in your browser

The resize is processed on your device with your browser’s image engine. Image Cosmos does not upload the selected file to its server. Choose JPG for photographs, PNG to keep transparency, or WebP for a compact web image. Review the real dimensions and file size shown beside the result before downloading.

How to resize an image for print or the web

1. Choose one JPG, PNG or WebP image. It stays in this browser tab. The limit is 25 MB and 40 megapixels.
2. For a screen size, keep Exact width and height or choose Percentage of original. For paper, choose Print size, pick centimetres, millimetres or inches, and type the width and height.
3. Set DPI to 72, 96, 150, 300 or Custom. Leave Keep aspect ratio ticked unless you mean to stretch the picture. Read the pixel size under the fields before you continue.
4. Select Resize image, check the width and height on the result, then download. JPG and PNG store the DPI you set. WebP keeps the pixels and does not store a DPI tag.

Pixels on screen and size on paper

A screen shows pixels. A printer thinks in millimetres or inches. Dots per inch, written DPI, is only the bridge between those two: it says how many pixels should sit in one inch of paper. It does not sharpen a photograph, and it does not invent detail the camera never captured. If you change the DPI number and leave the pixels alone, a website looks the same. Print software may simply print those same pixels larger or smaller.

This resizer does the useful half of that job. Choose Print size, type a width and height in centimetres, millimetres or inches, and set the DPI. The line under the fields updates before you press the button, so you can see the pixels you are about to create. The conversion is pixels = measurement × DPI ÷ 2.54 for centimetres, and ÷ 25.4 for millimetres. Inches are the measurement times the DPI. Each side is then rounded to the nearest pixel. One centimetre at 300 DPI is 118 pixels. One inch at 96 DPI is 96 pixels, and one inch at 72 DPI is 72 pixels.

JPG and PNG downloads also store that DPI as metadata, so a print program can open the file at the size you typed. A JPG receives a JFIF density in dots per inch. A PNG receives a pHYs chunk in pixels per metre, which is how PNG records the same idea. WebP files from this page do not carry a DPI tag. For WebP, and for any program that ignores metadata, the pixel dimensions are the size that matters. If a print shop asks for a file with a DPI label, choose JPG or PNG.

Common print sizes at 300 DPI

Three hundred DPI is the usual request for a photograph that will be printed and viewed up close: a passport-style photo, a 6 by 4 inch print, or an A4 sheet. The pixel counts below are width by height at 300 DPI, taken from the same conversion the button uses. A portal, school or lab can still ask for a different size, a kilobyte cap, or a particular crop. This table is the arithmetic, not an official specification.

A 35 by 45 millimetre frame is the size many UK, Irish and EU passport and visa photos ask for. At 300 DPI it is 413 by 531 pixels, because 35 × 300 ÷ 25.4 is 413.39, which rounds to 413, and 45 × 300 ÷ 25.4 is 531.50, which rounds to 531. That figure does not check that the head is the right height, the background is plain, or the file is under a portal limit. Use the crop tool if you need to remove space around the subject, resize the crop here, then use the image compressor if the form also caps the file. The 100 KB compressor is the same tool with a target already filled in.

A4 and A5 follow ISO 216. A4 is 210 by 297 millimetres and A5 is 148 by 210 millimetres, short side first in this table. At 300 DPI an A4 page is 2,480 by 3,508 pixels. That is a large canvas. The same A4 page at 150 DPI is only 1,240 by 1,754 pixels. If your original is smaller than the result, the print will look soft, because resizing cannot restore detail. For a document you will only read on screen, fewer pixels are enough and the file is lighter.

The 6 by 4 inch lab print is 1,800 by 1,200 pixels at 300 DPI. The 5 by 7 inch print is 1,500 by 2,100 pixels. A 10 by 15 centimetre print, the size many high-street labs still sell, is 1,181 by 1,772 pixels. Turn the aspect lock off only when you truly want those exact sides and you accept stretching. With the lock on, a photo that is not already that shape is scaled to fit inside the box, and one side may come out a little shorter than the number you typed. The pixel line tells you which of those two things is about to happen.

Which DPI to type

Seventy-two DPI is an old screen convention that some design files still carry. Ninety-six DPI is the figure behind a CSS inch on many systems: one inch in a style sheet is 96 CSS pixels, which is not the same thing as a ruler inch on your monitor. One hundred and fifty DPI can be acceptable for a large poster seen from across a room. Three hundred DPI is the right starting point for photos, passport pictures and text that someone will hold.

Going from 150 DPI to 300 DPI doubles each side and quadruples the number of pixels. That makes a bigger file, and it makes a smoother print only when the original actually contains those pixels. An 800 pixel snapshot enlarged to A4 at 300 DPI is still a small photo stretched across a sheet of paper. The DPI label will say 300, and the print will look soft. Start from the camera original, not from a picture you have already shrunk for a website or a chat app.

Screens do not use this label the way printers do. A page shows the pixel width you give it, then the layout scales that box. Embedding 300 DPI in a JPG does not make the image look sharper in a browser, and it does not make it a high-density display asset. For the web, pick the pixel width of the slot. A content image is often enough at about 1,200 to 1,600 pixels wide. A full-width hero can be 1,920 pixels wide. Exact canvases that people ask for by name are already set up on 1,920 × 1,080, 1,280 × 720, 1,200 × 1,200 and 800 × 800. Those pages run a fixed frame. This page is the one for a size you type yourself.

Fit, fill and stretch

Keep aspect ratio ticked when a face, a product or a document must not be squashed. In pixel mode, typing one side fills in the other. In print mode the same thing happens in centimetres, millimetres or inches. Untick the lock only for an exact width and height that is allowed to stretch. That is reasonable for a texture you are deliberately distorting, and it is the wrong control for a portrait.

This resizer never crops and never pads. If the destination is a fixed frame and the photo must cover every corner, that is a fill, which cuts the edges. If the whole photo must stay visible inside a frame of a different shape, that is a fit, which adds a background. Both of those live on the social media image resizer, which can crop to fill or fit the whole image on a background colour. Ready-made frames include the Instagram post, the Instagram portrait, the Instagram story and the YouTube thumbnail. Cut a custom area with the crop tool, then come back here if the cropped result still needs a print size.

File size, quality and privacy

Removing pixels usually makes the download smaller, but the format and the quality number decide the rest. JPG at the default quality of 82 is a practical photograph. A lower quality number throws away more fine detail and makes a smaller file. WebP behaves the same way on this page. PNG ignores the quality number and stays lossless, so a photograph saved as PNG often gets larger rather than smaller, while a flat logo may barely change. Enlarging adds pixels and often adds bytes. None of these settings aims at a kilobyte target. When the destination has one, resize to the pixels it asked for and then compress.

The work stays in this tab. The browser decodes the file, draws the new canvas and builds the download. Image Cosmos does not receive the image. One file at a time, up to 25 MB and 40 megapixels. A very large print canvas, such as a poster at 300 DPI, can hit that pixel ceiling. The page stops rather than freezing the tab. Keep the original as the master. Resizing the resized copy a second time, especially as a JPG, throws away a little more detail each time you save.

Frequently asked questions

How do I resize an image in cm or mm?

Choose Print size, then Centimetres or Millimetres, and type the width and height. Set the DPI the printer or form asked for. Photo prints are usually 300. The line under the fields shows the pixel size that size will become, using pixels = measurement × DPI ÷ 2.54 for centimetres and ÷ 25.4 for millimetres. Leave Keep aspect ratio ticked if the picture must not stretch.

How do I change the DPI without losing quality?

DPI is a label that tells print software how large to print the pixels you already have. Changing that label does not sharpen a photo, and asking for more pixels than the original contains enlarges it. Enlargement looks soft because the extra pixels are invented by scaling. You avoid that loss when the new pixel size is the same as the original or smaller. JPG and WebP are also saved again, so a low quality number can soften the file even at the same pixel size. PNG output is lossless. Keep the camera original as the master.

Does resizing an image reduce the file size?

Often, when you remove pixels, but it is not a promise and it is not a target in kilobytes. A wide camera JPG made narrower usually gets smaller at the same quality. A PNG of a photograph can stay large or grow, because PNG is lossless. Making the canvas bigger adds pixels and often adds bytes, without adding real detail. If a form says under 100 KB, set the pixel size here first, then use the image compressor on that download.

How do I resize an image without stretching it?

Leave Keep aspect ratio ticked. The other side follows the original proportions, in pixels and in centimetres, millimetres or inches. If you type a shape the photo does not have, the result fits inside that shape and one side can come out shorter. Untick the lock only when you want the exact width and height and you accept stretching. This page does not crop and does not add a coloured border. To cut a region, use the crop tool first. To fill a fixed frame or fit the whole picture on a background, use the social media image resizer.

Is this image resizer private?

Yes. The browser reads the file, draws the new size and offers a download in this tab. Image Cosmos does not receive the image, store a copy or keep a history of the job. Close or reload the page and the temporary download link is gone. The limit is one image at a time, up to 25 MB and 40 megapixels.

What pixel size is a 35 × 45 mm photo at 300 DPI?

413 × 531 pixels. The width is 35 × 300 ÷ 25.4, which is 413.39 and rounds to 413. The height is 45 × 300 ÷ 25.4, which is 531.50 and rounds to 531. That is a common passport and visa photo size in the UK, Ireland and the EU. It is the arithmetic only. It does not check head height, background colour or a portal file-size cap. Crop to the head and shoulders first if you need to, then resize, then compress if the form also limits kilobytes.

What DPI should I use for printing?

Use 300 DPI for photographs and text that someone will hold, including a 6 × 4 inch print, an A4 page and a 35 × 45 mm photo. Use 150 DPI only for a large poster seen from a distance, where the extra pixels of 300 are hard to tell apart. 96 DPI matches a CSS inch, and 72 DPI is an old screen convention. Neither is a sharp photo print. A website still displays the pixel width, not the DPI tag, so pick pixels for screen jobs and DPI for paper.