DPI is a single number stored in the header of a JPG or PNG. It tells a printer how many of the picture’s pixels to place in each inch of paper, and nothing else. Screens ignore it, upload portals rarely look at it, and changing it does not make a photo sharper or blurrier. Yet a notice that says “scan at 200 DPI” or a print shop that asks for “300 DPI” leaves many people with a file that reads 72 or 96, or carries no value at all.
This page rewrites that number. A JPG or PNG keeps its pixel data byte for byte: the tool only swaps the density field, so the width, height and quality are unchanged. If the form also states a size in pixels or centimetres, that is the part that decides how the picture looks, and it needs a resize before the DPI is set.
Before and after
2400 × 1602 px571 KBJPG
2400 × 1602 px571 KBJPG
The picture and its 2400 × 1602 px size stay the same. Only the DPI value in the file was set to 300, and EXIF and location data were removed.
At 300 DPI it prints at 20.32 × 13.56 cm (8 × 5.34 in).
The numbers are from a real run of the tool above. The pictures here are smaller previews of the actual files.
How to use it
- Add the photo, signature or scan whose DPI you need to change.
- Tap one of the common values (72, 96, 150, 200, 300, 600) or type any whole number up to 65535. The box starts at 300, the usual print figure.
- Press Set DPI. The result card shows the pixel size, which has not moved, and how many centimetres wide the picture now prints at the new value.
- Save the new file. Open it in the DPI checker if you want to see the stored number read back.
When “200 DPI” in a notice is really a pixel size
Recruitment notices often write DPI next to a centimetre size because the two together fix the pixel count: inches times DPI equals pixels. IBPS, SBI, NABARD and MIDC spell it out for the left thumb impression, “240 x 240 pixels in 200 DPI (preferred) i.e 3 cm * 3 cm”, and for the handwritten declaration, “800 x 400 pixels in 200 DPI (preferred) i.e. 10 cm * 5 cm”. The U.S. Department of State asks for a visa photo of 2 x 2 inches and, for the digital upload, 600x600 pixels minimum, which is the same square at 300 per inch. India Post’s GDS notification recommends a 320 × 400 pixel photo and gives the DPI as 72 to 150.
In each case the pixel figure is what the picture must have; the DPI explains where it came from. So make the pixels first, then label the file. Sometimes the numbers in a notice do not agree: TNPSC’s Group II notification asks for a 4.5 cm height x 3.5 cm width photo (170 pixels x 130 pixels) at 200 DPI, yet 4.5 cm at 200 DPI would be 354 pixels. When that happens, follow the pixel size and the KB limit, which are what an upload screen can measure, and then set 200 here so the file also states the value the notice names.
What stays the same and what is dropped
For an upright JPG or PNG the picture data is copied across unchanged, so there is no second round of compression and no loss. The new value is written in the JPG’s JFIF header or the PNG’s pHYs chunk. Blocks that can hold EXIF, GPS location, XMP or comments are removed on the way, which usually makes the file a few kilobytes lighter, never heavier by more than a few bytes.
HEIC, WebP, AVIF, GIF, BMP and TIFF files have no simple density field that forms read, so they are saved as a high-quality JPG first and the DPI is written into that. A phone JPG that relies on a hidden rotation flag is treated the same way, so it does not come out sideways once the EXIF is gone. In those cases the file size will differ from the original; the pixel dimensions still match.
Frequently asked questions
- Does converting from 72 to 300 DPI improve the quality?
- No. The pixels are the same before and after, so the picture looks identical on any screen. What changes is the printed size: a 1200 pixel wide photo is about 42 cm across at 72 DPI and about 10 cm at 300. Real extra detail can only come from a better original or a fresh scan at a higher setting.
- Will the KB size change when I set a new DPI?
- Barely, for a JPG or PNG. Only a header value is swapped and metadata is stripped, so the weight stays the same or drops slightly. If your form also has a KB limit, use a compress tool for that; the DPI value survives only if you set it after compressing, so do this step last.
- My form says 3.5 × 4.5 cm at 200 DPI. Is changing the DPI enough?
- Not on its own. That size works out to 276 × 354 pixels, and a phone photo is many times larger. Resize in centimetres with 200 as the DPI, which gives the right pixels and writes the value at the same time; this page is for when the pixels are already right and only the number is wrong.
- Can I convert the DPI of a PDF?
- No. This tool works on pictures only. If the PDF holds a single scanned page, export that page as a JPG or PNG with your PDF reader first, then set the DPI here.
- Is this the DPI setting of a gaming mouse?
- No. Mouse DPI is a sensor speed set in the mouse’s own software and has nothing to do with image files. This page only changes the print density stored inside a picture.