Check and change image DPI without changing a pixel
Application portals, print shops and publishers often ask for a photo “at 300 DPI”. This image DPI checker reads the resolution stored in JPG, PNG, BMP and TIFF files, shows how large the image will print at that setting, and lets you set a new DPI — 300 or any value — by rewriting only the header bytes. The image is not resampled, recompressed or resized: every pixel stays exactly as it was, and the tool re-reads the result to prove it.
It handles every place a resolution can hide: the JFIF header and EXIF tags in JPEGs, the Photoshop resolution block, the PNG pHYs chunk and the BMP header. All of them are updated together, so Windows, macOS, Photoshop and GIMP agree on the new value. Files are processed in your browser and never uploaded.
How to use the Image DPI Checker & Changer
- Drop one or more images onto the upload area, or click to choose them.
- Read each card: current DPI and where it comes from, the pixel size, and how big the image prints right now.
- Type a new DPI or pick a common value such as 300. To hit a physical size instead, enter a print width in cm, inches or mm.
- Check the “At … DPI” print size and the verification line under each card.
- Download each image, or all of them as a ZIP. File names get a suffix such as “-300dpi”.
Image DPI Checker & Changer features
No resampling
Only the resolution fields change. Pixel dimensions, colours and the compressed image data are byte-identical, so there is no quality loss.
Every resolution field
JPEG JFIF density, EXIF XResolution/YResolution, the Photoshop resolution block, PNG pHYs, BMP and TIFF headers are read and written together.
Print size at a glance
See the print size in inches and centimetres at the current DPI and at the new one.
Fit a print width
Enter “10 cm” and each image gets the DPI that makes it print 10 cm wide.
Conflict warning
If a file stores different DPI values in different places, you are warned — a common reason two apps disagree.
Batch and private
Change dozens of files at once and download a ZIP. Nothing is uploaded.
What DPI really changes
A digital image is a grid of pixels. DPI (dots per inch — strictly PPI, pixels per inch, for images) is only an instruction that says how many of those pixels should go into each printed inch. Print size = pixels ÷ DPI. A 3000 × 2000 px photo prints at 10 × 6.67 inches at 300 DPI, or at 41.67 × 27.78 inches at 72 DPI — it is the same file with the same detail either way.
That is why changing DPI here is instant and lossless, and also why it cannot make a small image sharper. If a 600 × 400 px photo must print at 300 DPI, it can only be 2 × 1.33 inches (5.1 × 3.4 cm). To print larger at 300 DPI you need more pixels: work out how many with the DPI calculator, and resize with the image resizer only if a form insists on exact pixel dimensions.
Common DPI requirements
| Use | Typical DPI | What it means for pixels |
|---|---|---|
| Photo prints and photo books | 300 | 6 × 4 in needs 1800 × 1200 px |
| Passport and visa photos (print) | 300 | 35 × 45 mm needs 413 × 531 px; 2 × 2 in needs 600 × 600 px |
| Magazines and brochures | 300–350 | A4 at 300 DPI needs 2480 × 3508 px |
| Posters viewed from a distance | 150–200 | A2 at 150 DPI needs 2480 × 3508 px |
| Screens, web and email | Ignored | Only the pixel size matters on screen |
| Scanned documents and line art | 300–600 | Higher DPI keeps thin lines crisp |
Where a JPEG stores its DPI — and why apps disagree
A JPEG can carry its resolution in up to three places: the JFIF header (density and unit), the EXIF tags XResolution, YResolution and ResolutionUnit, and Photoshop’s own resolution block. Different programs read different ones, so a file saying 72 in EXIF and 300 in JFIF can show as 72 DPI in Windows and 300 DPI elsewhere. This tool lists every value it finds, flags conflicts and writes the new DPI into all of them. If a JPEG has no resolution fields at all, a standard JFIF header is added.
PNG stores resolution in the pHYs chunk as pixels per metre, so 300 DPI is saved as 11,811 px/m and reads back as 299.9994 — shown as 300. WebP and GIF have no DPI field, and HEIC files cannot be edited here; convert them to PNG or JPG first. For a full report on pixel size, megapixels and print suitability, use the image resolution checker.
Image DPI Checker & Changer FAQ
How do I check the DPI of an image?
Drop the image into this image DPI checker. The card shows the current DPI and where it was found (JFIF, EXIF, Photoshop or PNG pHYs), the pixel size and the print size at that DPI. “Not set” means the file stores no resolution, and most apps then assume 72 or 96 DPI.
How do I convert an image to 300 DPI?
Choose 300 in “Common values” (it is the default) and download the file. The DPI fields are rewritten to 300 without resampling, so the pixel dimensions and quality stay the same.
Does changing DPI reduce quality?
No. Only the header changes; the compressed image data is byte-identical, which the tool verifies by comparing it with the original.
Will 300 DPI make my photo sharper when printed?
No. Sharpness depends on the number of pixels. Setting 300 DPI simply makes the print smaller and denser. If the result is too small, you need a higher-resolution original.
Why does Windows show a different DPI from Photoshop?
JPEGs can store resolution in the JFIF header, EXIF and a Photoshop block, and programs read different ones. The checker lists all of them and the download writes the same value everywhere.
Are my images uploaded?
No. Files are read and edited in your browser, and nothing is sent to a server.