I typed 10 into a width box and picked centimetres. The download came back 10 pixels wide. A red square. Useless for print. The page had mixed two units that do not convert without a third number.
A centimetre is a length on paper. A pixel is a dot on a screen. DPI is how many of those dots you put in an inch. Skip the DPI and you are guessing. This tab will not guess.
The new page is Resize Image. You can type pixels, or a percent, or centimetres at a DPI you can see. Presets. A batch ZIP. The preview is the real output size. The photo stays in this tab.
The 10 that had no unit
Most resizers give you one pair of boxes. Width and height. The label says px, or it says nothing. You type 10 because you meant 10 cm for a small print, and the file that lands on disk is 10 by 8.
Nothing crashed. The form accepted the number. The canvas drew 10 pixels. The download was technically correct for the unit the page had decided you meant.
A centimetre is a length on paper. A pixel is a dot on a screen.
I wanted the other unit. The page never asked.
That is the whole product. Show the unit. If the unit is centimetres or inches, show the DPI too. Refuse to invent pixels from a length.
What the phone app actually is today
Image Size has been on the App Store since 1 September 2013. I looked the listing up on 16 September 2026. Track id 670766542. Seller Vitalij Schaefer. Version 16.2, dated 26 August 2026. Free. 29,772 ratings. Average 4.74.
The description on that lookup says you can resize in pixels, millimetres, centimetres or inches. It also says ads can be removed with a one-time in-app purchase. I did not open checkout, so I am not printing a dollar figure. I am printing what the listing said.
People still search for that job. Resize a photo to 1280 by 720. Print it on A4. The phone app is one way to do it. A tab that never takes the photo off the computer is another.
Pixels, percent, paper
Pixels is a canvas. Percent is a scale. Paper is a length plus a DPI. Those are not aliases of each other.
Pixels is a canvas. 1280 by 720 is 1280 by 720. If the original is 4:3, fit inside pads the leftover. Stretch fills the rectangle and changes the ratio. Lock aspect keeps the original ratio and computes the missing side.
Percent is a scale. Fifty percent of 1600 by 1200 is 800 by 600. Both sides move together. That is the default on a first visit, so the sample actually changes.
Paper is a length plus a DPI. 21 cm at 300 DPI is 2480 pixels. 29.7 cm at 300 DPI is 3508. Those two numbers are A4, from ISO 216, 210 by 297 millimetres, rounded through 25.4 millimetres per inch. Type centimetres without a DPI and this page throws. It will not pick 72 for you in silence.
The inch in the middle
25.4 millimetres in an inch. That constant is the only reason centimetres become pixels.
pixels = round(cm / 2.54 * DPI)
21 / 2.54 * 300 is 2480.31496, which rounds to 2480. 29.7 / 2.54 * 300 is 3507.874, which rounds to 3508. I put those in a test so a later rounding change cannot quietly move A4. If those two numbers drift, the page does not ship.
72 DPI is a screen default from a long time ago. 300 DPI is a common print density. Neither is magic. The page defaults to 300 because that is what people type for a print. You can set 72 through 1200. Below 72 it clamps. Above 1200 it clamps. Safari also stops a canvas at 16,777,216 pixels, so an A4 at 600 DPI gets scaled down and the line under the knobs says so.
A4 is millimetres, 3 by 4 is centimetres
I am not inventing a country's passport crop. 3 by 4 centimetres at 300 DPI is 354 by 472 pixels. That is an ID-photo size at the DPI you set. If a consulate wants a different millimetre box, type those millimetres.
A4 is not a guess either. ISO 216. 210 mm by 297 mm. The Images to PDF tool already used those millimetres for paper. Resize Image uses the same millimetres, then multiplies by DPI, because here the output is a bitmap, not a PDF page.
Letter is 8.5 by 11 inches. Switch the unit to inches and type those. Same DPI box. Same refusal if the DPI is missing.
What YouTube printed this morning
YouTube's help page for custom thumbnails, support.google.com/youtube/answer/72431, read 16 September 2026:
| What they ask | The number |
|---|---|
| 16:9 video | 3840 by 2160 |
| Shorts | 2160 by 3840 |
| Minimum width | 640 |
| Format | JPG or PNG |
| Phone upload | 2 MB |
| Desktop upload | 50 MB |
The 1280 by 720 preset is the same 16:9 shape at a size that still fits that 2 MB phone cap more often. Both presets sit on the page. If YouTube changes the help article, type the new pixels. The preset is a shortcut, not a contract with Google.
LinkedIn did not print a number
I opened LinkedIn's own help in this sitting. It did not give me a pixel size for a personal background. Size guides that cite LinkedIn use 1584 by 396. That is the banner preset. If their help page starts printing a different pair tomorrow, type that pair.
Microsoft Learn does print a range for a Teams custom background: PNG or JPEG, at least 360 by 360, at most 3840 by 2160. 1920 by 1080 sits inside that box at 16:9. The preset is 1920 by 1080, not a claim that Teams requires exactly that.
Instagram feed is 1080 square because that is what people type. I did not find a WhatsApp help page that prints a profile pixel size today, so there is no WhatsApp-branded preset. There is a 640 square if you want a small square. That is all it is.
Fit inside is not a crop
A lot of "resize" pages crop. You pick 16:9, they cut the top and bottom off a 4:3 photo, and they call it a resize.
This page has two fits.
Fit inside draws the whole photo into the canvas and pads the leftover. White, black, or transparent, except JPEG cannot hold transparent, so JPEG pads white or black.
Stretch fills the canvas. The ratio can change. The photo is not cut. It is squashed or stretched.
There is no cover mode. Cover is a crop. Crop is a different tool, and it is not this one. The line under the knobs says "Fit inside with pad bars. This is not a crop." when the ratios differ.
A bigger canvas is not a sharper photo
200 by 100 into 400 by 200 looks twice as wide in the preview. It is the same scene, spread over more pixels. I show the result at the real output size, so the softness is visible before you save. The line says when the canvas is larger than the original.
Safari's canvas cap is 16,777,216 pixels. I did not pick that number for fun. That is the product limit on iPhone Safari. An 8000 by 6000 original at 100 percent is 48 million pixels. The page scales it down and says it clamped.
Quality on JPEG and WebP is a slider. PNG stays lossless. The KB next to the preview is canvas.toBlob output, not an estimate. The file you download is that blob.
One photo, or a ZIP
One file downloads as name-1280x720.jpg. Two or more become resized-N-images.zip. Cap is 100 files and 40 MB each. JPEG, PNG, WebP, iPhone HEIC. GIF is refused. A PDF in the same drop is refused, because it is already a document.
HEIC uses the same decoder as HEIC to JPG. Safari can read it in the tab. Chrome and Firefox load a decoder module the first time a HEIC file is in the drop. You will see that load. The module does not send the photo anywhere.
Stop cancels the run. Nothing is saved until you download.
The sample is drawn here
A first visit should still produce a real file. The sample is a 1600 by 1200 still, 4:3, drawn on a canvas in this tab. A navy field, a light rectangle, a red square, the size written on it. It is not a stock photo from a CDN. Fifty percent of that is 800 by 600. Download it. The name is sample-1600x1200-800x600.jpg. Replace it with your own drop. If you never drop a file, you still leave with a JPEG you can open.
I did that so the knobs are not dead until you find a file. The sample is also the test. If 50 percent of 1600 by 1200 is not 800 by 600, the unit tests fail before the page ships.
The KB is the download
A lot of resizers show a slider and a guessed size. This page encodes with the browser's own canvas.toBlob, then shows that byte count. Change quality, run again, the KB next to the preview is the blob you are about to save.
I looked at WASM codecs. They are extra bytes to fetch before the first resize. For JPEG, PNG, WebP, the canvas already knows how. pica does the scale. The encode stays in the tab.
The preview is not a thumbnail of the result. It is the result, at the output pixels, in a scrolling box. A 1280 by 720 JPEG is 1280 pixels wide on that page. If your window is narrower, you scroll. That is the point. A card that shrinks 3840 by 2160 down to 400 CSS pixels will lie about sharpness.
Settings in the URL, photo not
Mode, size, DPI, fit, format and pad sit in this browser under softery.resize-image.settings. Copy settings link puts those knobs on the URL. You see the URL in a box before it hits the clipboard. The photo is not in it.
That is the share for "YouTube thumbnail, 1280 by 720, JPEG, fit inside." It is not a share of someone's holiday pictures.
Clear settings puts the knobs back to 50 percent, 300 DPI, JPEG. Clear photos drops the files. Two different buttons, on purpose.
Mixpanel and Google Analytics load with Softery.io. They see that someone opened the tool, which setting moved, and whether a download happened. They do not get the photos. Sizes go out as buckets. The image never becomes a property.
What I checked, and what I did not
| Claim | Source, 16 September 2026 |
|---|---|
| Image Size, 29,772 ratings, 4.74, Free | iTunes lookup id=670766542 |
| Ads removable via a one-time IAP | Same listing description |
| YouTube 3840 by 2160, min width 640, 2 MB phone | YouTube help article 72431 |
| A4 210 by 297 mm | ISO 216, already in the PDF tool |
| 3 by 4 cm at 300 DPI = 354 by 472 | 25.4 mm per inch, rounded |
| Safari canvas 16,777,216 | The same cap the cutout tool uses |
| 40 MB, 100 files | This page's own limits |
I did not open Image Size's IAP sheet, so there is no yearly price here. I did not load a WhatsApp help page that printed a DP size. I did not treat a Canva blog as LinkedIn's help article. The LinkedIn preset is labeled as 1584 by 396 from size guides, and the copy on the tool page says so.
Try the tab
- Open Resize Image.
- Keep the sample, or drop a JPEG, PNG, WebP or HEIC.
- Pick pixels, a percent, or centimetres at a DPI you can see.
- Hit Resize. The preview is the real output size. The KB next to it is the file you will download.
Nearby tools
An iPhone HEIC you want as a JPEG, not as a smaller HEIC, belongs on HEIC to JPG. Photos that should become pages belong on Images to PDF. A cutout, not a resize, belongs on Background Remover.
Resize Image is the thirty-sixth free tool on the hub. It runs after the JavaScript has loaded. Unplug the cable if you want. The photo is still in the tab.
Last updated: September 16, 2026 | Reading time: 10 minutes
Written by Softery.io, after a 10 cm width turned into a 10 pixel square.