What DPI means and how to change an image to 300 DPI

DPI (dots per inch) is a number stored in an image file that tells a printer how many pixels to fit into each inch of paper. It does not make a picture sharper: a photo has exactly the same pixels at 72 DPI and at 300 DPI, and only its print size changes. Print size is pixels divided by DPI, so a 4 x 6 inch print at 300 DPI needs 1200 x 1800 pixels. To change the number without touching the pixels, turn off Resample in Photoshop or Preview, use Image > Print Size in GIMP, or use our free change image DPI tool in any browser.

How to change DPI: quick answer by app

App	Where to set the DPI	Do the pixels change?
Photoshop	Image > Image Size, deselect Resample, type the Resolution	No
Photoshop, Resample on	Image > Image Size with Resample selected	Yes, pixels are added or removed
GIMP	Image > Print Size, X resolution and Y resolution	No, never
Mac, Preview	Tools > Adjust Size, deselect Resample image, type the Resolution	No
Windows 11, File Explorer	Right-click > Properties > Details shows the DPI	Not a DPI setting, see below
Any browser	Our change image DPI tool	No, for JPG, PNG, BMP and TIFF

The rows marked No are what you want when a printer, a print shop or a form only asks for a DPI value. The row marked Yes changes the picture itself, which is a different job: shrinking a photo for an upload, or enlarging one, which adds no detail (see the section on upscaling below).

What DPI means, and DPI vs PPI

Strictly, DPI counts the ink dots a printer lays down per inch, and PPI counts the pixels of an image per inch of print. GIMP’s manual warns not to confuse the image’s output resolution with the printer’s resolution, which is given in dpi (GIMP). Adobe measures image resolution in pixels per inch (Adobe), and Photoshop’s field is simply called Resolution. Upload forms, Windows and most people say DPI for the same number, so in this guide DPI and PPI both mean pixels per printed inch.

The number lives in the file’s header, next to the picture. A JPG stores it in its JFIF header as dots per inch or dots per centimeter (JFIF), and often again in the Exif data a camera writes. A PNG stores it in a pHYs chunk, which the PNG standard describes as the intended pixel size, counted in pixels per meter (W3C). So 300 DPI is stored in a PNG as 11,811 pixels per meter. A file can also hold no DPI at all. That is not a fault: it simply has no print size of its own until you set one.

Why changing the DPI does not change sharpness

Sharpness depends on how many pixels hold the detail. The DPI only decides how those pixels are spread over paper. Adobe explains that a digital image holds a fixed amount of image data but no fixed physical size or resolution, and that changing the resolution changes its physical dimensions (Adobe). Here is one 1200 x 1800 pixel photo at five DPI values:

DPI stored in the file	Prints at (inches)	Prints at (cm)	Pixels
72	16.67 x 25	42.3 x 63.5	1200 x 1800
150	8 x 12	20.3 x 30.5	1200 x 1800
200	6 x 9	15.2 x 22.9	1200 x 1800
300	4 x 6	10.2 x 15.2	1200 x 1800
600	2 x 3	5.1 x 7.6	1200 x 1800

On screen all five look identical, and the file size hardly moves: in our test, setting 300 DPI with our tool left the file the same size, or 18 bytes larger when a JPG had no JFIF header yet. What changes is the print. At 300 DPI each pixel is 1/300 of an inch wide, so the same detail is packed into a smaller, denser print than at 72 DPI.

Print size = pixels ÷ DPI

Two formulas cover every case:

• Print size in inches = pixels ÷ DPI
• Pixels needed = inches × DPI, or millimeters ÷ 25.4 × DPI, because an inch is exactly 25.4 mm (NIST)

So 300 DPI is not a pixel size on its own. It becomes one only once you add a print size. These are the pixels common prints need, rounded to the nearest pixel. The sizes are portrait, so swap the two numbers for landscape.

Print size	At 150 DPI	At 200 DPI	At 300 DPI
4 x 6 in (10.2 x 15.2 cm)	600 x 900	800 x 1200	1200 x 1800
5 x 7 in (12.7 x 17.8 cm)	750 x 1050	1000 x 1400	1500 x 2100
8 x 10 in (20.3 x 25.4 cm)	1200 x 1500	1600 x 2000	2400 x 3000
US Letter, 8.5 x 11 in	1275 x 1650	1700 x 2200	2550 x 3300
A4, 210 x 297 mm	1240 x 1754	1654 x 2339	2480 x 3508
Passport photo, 35 x 45 mm	207 x 266	276 x 354	413 x 531
2 x 2 in photo	300 x 300	400 x 400	600 x 600

A4 is 210 x 297 mm and US Letter 8.5 x 11 inches, as the W3C page size definitions give them (W3C). For A4 at 300 DPI: 210 ÷ 25.4 × 300 = 2480.3 and 297 ÷ 25.4 × 300 = 3507.9, so 2480 x 3508 pixels. For a 35 x 45 mm passport photo: 35 ÷ 25.4 × 300 = 413.39 and 45 ÷ 25.4 × 300 = 531.496, so 413 x 531 pixels. Our passport photo size guide has every country’s size worked out the same way.

Going the other way, a 4032 x 3024 pixel photo (about 12 megapixels) prints at 13.44 x 10.08 inches at 300 DPI, about 34 x 26 cm, and at 56 x 42 inches if its file says 72 DPI. A photo with fewer pixels than the table asks for can still be printed at that size, only at a lower DPI: 800 x 1200 pixels on a 4 x 6 inch print works out to 200 DPI. Adobe recommends 300 PPI for the best print quality unless your printer requires a different value (Adobe).

How to check the DPI of an image

• Windows 11: in File Explorer, right-click the image, select Properties, then open the Details tab. Under Image, Horizontal resolution and Vertical resolution show the DPI, next to Width and Height in pixels. We checked these labels in File Explorer on Windows 11; Microsoft documents the property behind them as the number of pixels per resolution unit across the image width (Microsoft).
• Mac: open the image in Preview and click the Info button in the toolbar. Apple says the Inspector shows details such as the image resolution (Apple). Tools > Adjust Size also shows a Resolution field (Apple).
• Photoshop: Image > Image Size shows the Resolution next to the width and height (Adobe).
• GIMP: Image > Print Size shows the X resolution and Y resolution (GIMP).
• Any browser: drop the file on our change image DPI page. It shows the pixels, the DPI and the part of the file it came from, plus the print size at that DPI and at 72, 150 and 300.

Different apps can show different numbers for the same JPG, because a JPG can hold its DPI in up to four places: the JFIF header, the Exif data cameras and phones write, a resolution block Photoshop adds and XMP data from editing programs. Each app reads its own favorite first; Photoshop, for one, reads its own block. Our tool lists every value it finds, and when it saves, it writes the new DPI into all of them.

Many photos say 72 DPI. That is a common default written when no print size was chosen, and it says nothing about quality.

How to change DPI in Photoshop

Without changing the pixels

1. Choose Image > Image Size.
2. Deselect Resample to keep the current pixel dimensions.
3. Type the new Resolution, for example 300.
4. Select OK (Adobe).

Because the pixel count is fixed, the print width and height adjust to match the new resolution (Adobe). Raise it from 72 to 300 and the print gets about four times smaller in each direction, with no pixel changed.

Changing the pixels (resampling)

With Resample selected, Photoshop changes the pixel dimensions instead. Adobe describes this as resizing for web, mobile or screen, and says it changes the total pixels and the file size (Adobe). Photoshop then interpolates the pixel information (Adobe). That is the right tool for shrinking a large photo to the pixel size a form asks for, and the wrong one for making a small photo sharper, as explained below.

How to change DPI in GIMP

1. Choose Image > Print Size.
2. Type the new X resolution. With the chain symbol linked, the Y resolution follows. Width and Height show the print size that results, in the unit you pick from the list.
3. Confirm, then export the image as you normally would.

GIMP’s manual says this command does not change the number of pixels in the image and does not resample it (GIMP). To change the pixels, GIMP uses Image > Scale Image instead (GIMP).

How to change DPI on a Mac with Preview

1. Open the image in Preview.
2. Choose Tools > Adjust Size.
3. Deselect Resample image.
4. Type the new value in Resolution, confirm, and save the file.

Apple says to deselect Resample image to make the dimensions smaller without losing any detail (Apple). Resampling is what changes the pixel count (Adobe), so with it off only the resolution and the print size change. With Resample image selected, a smaller Resolution removes pixels instead, which Apple gives as the way to reduce an image’s file size.

On Windows, File Explorer shows the DPI as described above, but the Microsoft help pages we checked do not describe a way to change it there or in Paint or Photos. Use Photoshop, GIMP or our browser tool.

How to change DPI online with our tool

1. Open change image DPI and pick, drop or paste your images, up to 30 at once.
2. Read the line for each image: its format, its pixel size, the DPI stored in it and the print size that gives.
3. Tap 300 DPI, or 72, 96, 150, 200 or 600, or type any whole number from 1 to 65,535. The print size table updates as you go.
4. Select Download, or Download all (.zip) for several files.

The tool changes only the header of JPG, PNG, BMP and TIFF files, so every pixel and the image quality stay exactly as they were, and it reads the saved copy back to confirm the new DPI before you download it. WebP, AVIF and GIF have no DPI field most programs read, so it saves those as PNG. HEIC photos from an iPhone open only in browsers that can decode them; if you get an error, convert them with HEIC to JPG first. Everything runs in your browser, so the files are not uploaded.

To set the pixels and the DPI together from a size in centimeters or inches, use resize image in cm and KB.

When a form asks for 200 or 300 DPI

A form that mentions DPI is usually telling you how to scan, or how its centimeter sizes turn into pixels. The IBPS notice for bank PO/MT recruitment is a good example. It asks you to set the scanner to a minimum of 200 dpi, and it gives sizes such as a left thumb impression of 240 x 240 pixels in 200 DPI, which it says is 3 x 3 cm, and a handwritten declaration of 800 x 400 pixels in 200 DPI, or 10 x 5 cm (IBPS). The DPI explains where the pixel numbers come from: 3 cm at 200 DPI is 3 ÷ 2.54 × 200 = 236 pixels, which IBPS rounds to 240.

Passport uploads usually set pixels and no DPI at all. India’s Passport Seva guideline asks for 630 x 810 pixels (Passport Seva), and GOV.UK asks for a digital photo at least 600 pixels wide and 750 tall (GOV.UK).

What to do:

1. The form gives pixels. Match them. Set the DPI too if the instructions name one; it costs nothing and some checkers read it.
2. The form gives centimeters and a DPI. Convert: 3.5 x 4.5 cm is 276 x 354 pixels at 200 DPI and 413 x 531 pixels at 300 DPI. Resize image in cm and KB does the conversion, writes the DPI into the JPG and fits a KB limit at the same time.
3. The form says to scan at 200 or 300 DPI. Set your scanner to that before you scan. Changing the number afterwards adds no detail, while scanning at that setting does.
4. The form only says 300 DPI. Set it with our DPI tool and keep whatever pixels and KB the rest of the instructions allow.

For a printed passport photo, the passport photo maker saves the 35 x 45 mm format as 413 x 531 pixels with 300 DPI stored in the file. If the form also limits the file size, our guide on how to reduce a photo’s size in KB covers that step.

Why upscaling a small photo to 300 DPI adds no detail

There are two ways to get a small photo to “300 DPI”, and neither one adds detail:

• Change only the number. A 276 x 354 pixel photo set to 300 DPI prints at about 2.3 x 3.0 cm instead of 3.5 x 4.5 cm. It stays as sharp as it was, but it prints small.
• Resample it up to 413 x 531 pixels. It now prints at 35 x 45 mm, but the new pixels are estimates. Adobe says that when you upsample, new pixels are added based on the color values of existing pixels, and the image loses some detail and sharpness (Adobe). GIMP says enlarging does not add any new detail (GIMP).

Adobe’s advice is to avoid upsampling by scanning or creating the image at the resolution your printer or output needs (Adobe). In practice: rescan the print at 300 DPI, use the original photo from your camera instead of a smaller copy from a chat app, or take a new photo. For an official photo, take a new one rather than enlarging a small copy.

Common DPI problems and fixes

• The photo says 72 DPI. Nothing is wrong with it. Set 300 if a printer or form asks for it, and check that the pixels are enough for your print size.
• Two apps show different DPI values. The file stores the DPI in more than one place and the values disagree. Save it once with our DPI tool, which writes the same value everywhere.
• The file size did not change after setting 300 DPI. That is expected. The DPI is a few bytes in the header. To change the KB, change the pixels or the JPEG quality.
• The print came out tiny or huge. Divide the pixels by the DPI stored in the file. A 600 x 600 pixel photo at 72 DPI prints at 8.33 inches square, and at 300 DPI at 2 inches square.
• A form still rejects a 300 DPI photo. It is checking something else: the pixel size, the file size in KB or the format. Our KB guide lists the usual causes.
• A file has no DPI at all. It has no print size of its own yet. Saving it with our DPI tool adds one, and the tool says so when none was stored.