📐 Image Resizer
An image resizer by pixels, percentage, inches or millimeters at a chosen DPI, with presets for Instagram, YouTube, passport and print. In-browser.
Choose an image, or drop it here
Resized in this tab. The file is never uploaded.
What Image Resizer Does
Resizing an image is resampling: the resizer computes new pixels from the old ones. Making an image smaller is well-conditioned — several source pixels are averaged into each new one, and the result is genuinely sharper than the original per pixel. Making it larger is not. There is no extra information to draw on, so the new pixels are interpolated guesses, and the picture gets softer. No amount of algorithm changes that; enlargement is invention.
Most people arriving at a resizer already know the size they need, and it is usually not in pixels. It is "2 by 2 inches for a passport", "4 by 6 for printing", "1080 by 1080 for Instagram". The step that goes wrong is the conversion, because inches only become pixels once you fix a resolution: at 300 DPI a 2-inch edge is 600 pixels, at 150 DPI it is 300.
So this tool takes the unit you actually have — pixels, percent, inches or millimeters — converts it with the DPI you choose, and shows the resulting pixel size before you commit. The presets are the sizes people name, with the arithmetic already done.
Units matter more than they look. Web uploads are quoted in pixels, print shops in inches, and government and exam portals very often in centimeters — 3.5 × 4.5 cm is the most requested ID photo size there is. All four go in directly, so nobody has to do the conversion by hand.
One further step the pixel dimensions alone do not cover: the resolution is written into the saved file. A canvas-encoded JPG normally claims no physical resolution at all, and a canvas-encoded PNG carries no resolution chunk, so a portal that validates the embedded DPI rejects the image however many pixels it has. The encoded bytes are patched afterwards — the JFIF density fields in a JPG, a pHYs chunk in a PNG — so the file really does declare the number you set.
It also tells you two things competitors leave you to discover afterwards: when the target is bigger than the original, and when the target shape does not match the original shape and the picture will be stretched.
How to Use Image Resizer
- Add an image, or drop it onto the box
- Choose the unit — pixels, percent, inches or millimeters — and set the DPI if you picked a print unit
- Type the width or height, or choose a preset such as 1080×1080 or a 2×2 inch passport photo
- Pick an output format and quality, then resize and save
Formula Used by Image Resizer
Physical size to pixels
pixels = inches × DPI (millimeters: pixels = mm ÷ 25.4 × DPI)
- DPI
- dots per inch — how densely the pixels will be laid down when printed
- 25.4
- millimeters in an inch, exact by the 1959 international definition
Worked example
A 2 × 2 inch passport photo at the 300 DPI print labs ask for.
- 2 in × 300 DPI = 600 px
- 2 in × 300 DPI = 600 px
Result: 600 × 600 pixels — not 2 × 2, and not 200 × 200, which are the two answers people reach for.
Keeping the proportions
height = width × (originalHeight ÷ originalWidth)
- originalHeight ÷ originalWidth
- the aspect ratio, held constant so the image is not stretched
Worked example
A 4032 × 3024 phone photo (4:3), resized to 1600 px wide.
- 3024 ÷ 4032 = 0.75
- 1600 × 0.75 = 1200
Result: 1600 × 1200. Asking for 1600 × 1600 instead would squash the picture by a third.
Print sizes in pixels at 300 DPI
The resolution print labs and most government portals expect. At 150 DPI, halve every number.
| Use | Physical size | Pixels at 300 DPI |
|---|---|---|
| Passport / visa photo (US, India) | 2 × 2 in (51 × 51 mm) | 600 × 600 |
| Standard photo print | 4 × 6 in | 1200 × 1800 |
| Medium photo print | 5 × 7 in | 1500 × 2100 |
| Large photo print | 8 × 10 in | 2400 × 3000 |
| A4 page | 210 × 297 mm | 2480 × 3508 |
| A5 page | 148 × 210 mm | 1748 × 2480 |
ID and application-form sizes
The sizes portals name, already converted. Always use the exact figure your form states — these are the common ones, not a standard.
| What the form asks for | Pixels | Note |
|---|---|---|
| 3.5 × 4.5 cm photo at 300 DPI | 413 × 531 | The most commonly requested ID photo size |
| 3.5 × 4.5 cm photo at 200 DPI | 276 × 354 | Some portals specify 200 rather than 300 |
| 2 × 2 in photo at 300 DPI | 600 × 600 | US passport and visa convention |
| Form photograph | 200 × 230 | Quoted directly in pixels by many Indian government forms |
| Form signature | 140 × 60 | Quoted directly in pixels alongside the photo |
| Profile picture | 512 × 512 or 300 × 300 | Square, so crop before resizing if your photo is not |
Screen and social sizes
Platform requirements change; these are the long-standing values the presets use.
| Where | Pixels | Aspect |
|---|---|---|
| Instagram square post | 1080 × 1080 | 1:1 |
| Instagram portrait post | 1080 × 1350 | 4:5 |
| Instagram / TikTok story | 1080 × 1920 | 9:16 |
| YouTube thumbnail | 1280 × 720 | 16:9 |
| LinkedIn banner | 1584 × 396 | 4:1 |
| Full HD screen | 1920 × 1080 | 16:9 |
How to Read Your Result
DPI does nothing to a file that stays on screen
A 600 × 600 image is 600 × 600 pixels whatever DPI is written in its header. The number only decides how large those pixels are when printed. For anything shown on a display, set the pixel dimensions directly and ignore DPI entirely — including the "72 DPI for web" advice, which is a Macintosh convention from the 1980s and has no technical meaning today.
The exception: a portal that checks the tag
A validator does not care that DPI is meaningless on screen — it reads the field and rejects the file if it does not say 300. That is why the number is written into the output here rather than only used for the arithmetic. Set the DPI your form names, save as JPG or PNG, and the file will declare it.
Resize and crop are different operations
If the shape you need does not match the shape you have, resizing alone cannot get you there without distortion. A 4:3 photo made 1080 × 1080 is squashed by a quarter. The honest sequence is crop to the target ratio first, then resize to the target pixels.
Enlargement has a usable range
Ten to twenty percent generally passes unnoticed. Doubling is visibly soft. Beyond that you are producing a larger file containing no more information, which is worse than sending the original and letting the display scale it.
Limitations & Accuracy Notes
- Resampling uses the browser’s built-in high-quality scaler. It is good, and it is not a machine-learning upscaler — nothing here invents plausible detail.
- The DPI is written into JPG (the JFIF density fields) and PNG (a pHYs chunk), but not into WebP, which has no standard field for it. Save as JPG or PNG when a portal validates the embedded resolution.
- Cropping is not part of this tool. When the target aspect differs from the original, the mismatch is flagged but the image is scaled to fit the numbers you gave.
- EXIF, including orientation and GPS, is not carried into the output. Rotation from the EXIF tag is applied to the pixels first, so the picture comes out the right way up.
- One image at a time — this tool is built around per-image dimensions rather than batch settings.
Frequently Asked Questions
What size is a 2x2 inch passport photo in pixels?
What does DPI actually change in a digital file?
Can I enlarge an image without losing quality?
How do I resize without stretching the picture?
Is 72 DPI the right setting for web images?
Are my images uploaded to a server?
References & Further Reading
- MDN — createImageBitmap() — The decode path, including the imageOrientation option that applies EXIF rotation before resizing
- MDN — HTMLCanvasElement.toBlob()
- MDN — Image file type and format guide — Format-by-format capabilities, including which support transparency