How to Change Image DPI on Mac (Without Losing Quality)

To change an image's DPI on a Mac without changing its quality, open it in Preview, choose Tools → Adjust Size, untick Resample image, type the new value in Resolution and save. The pixels stay exactly the same; only the number that tells a printer how many of them to fit into an inch changes. That single fact — DPI is a label, not detail — decides which of the four methods below you should use and whether changing it will fix your problem at all.

Quick comparison

How to check an image's current DPI

Before changing anything, find out what the file says now — the fix may already be done, or the file may not carry a DPI at all.

• Preview: open the image and press ⌘I (Tools → Show Inspector). The General Info tab lists Image DPI next to the pixel size.
• Terminal: sips -g dpiWidth -g dpiHeight image.png prints both values. A file with no stored resolution reports 72, because that is what macOS assumes.
• ImageMagick (if installed through Homebrew): identify -format "%x x %y %U\n" image.png. PNGs are shown in pixels per centimetre — 118.11 means 300 DPI.
• In the browser: drop the file on our DPI Converter. It tells you which part of the file the value came from, which is useful when two apps disagree about the same JPEG.

If every tool already reports 300 and the print still looks soft, the problem is pixel count, not DPI — skip to the pixel table below.

What DPI is, in one paragraph

A digital image is a grid of pixels. DPI — dots per inch, often used interchangeably with PPI — is one number stored in the file that says how many of those pixels should be printed per inch of paper. Print width in inches is simply pixel width divided by DPI. A 3000-pixel-wide photo prints 10 inches wide at 300 DPI and about 41.7 inches wide at 72 DPI. The picture is identical in both cases; only the paper size changes. Screens, browsers, slide software and chat apps ignore the number entirely and lay the image out by its pixels.

So when a print shop, a publisher or an online form asks for "300 DPI", two different things can be going on:

1. The file just needs to say 300. The image already has enough pixels, and a checker is reading the metadata. Changing the label solves it.
2. The image needs enough pixels to print sharply at 300 DPI. Then the label is irrelevant and what matters is pixel count — see the table in the next section.

Every method below can do the first. None of them can truly do the second: adding pixels to a small image makes it bigger, not sharper.

How many pixels a print needs

Multiply the print size in inches by the DPI:

If your image meets the 300 DPI column, you only need to change the label. If it doesn't, decide whether a smaller print or a lower DPI (150 is common for posters viewed from a distance) is acceptable before you reach for enlarging.

Method 1: Preview (built into macOS)

Preview can change DPI in place, and it is the fastest option for a single file.

1. Open the image in Preview (double-click it, or right-click → Open With → Preview).
2. Choose Tools → Adjust Size….
3. Untick "Resample image" at the bottom of the dialog. This is the step that matters: with it off, Width and Height in pixels are locked and only the resolution changes. With it on, Preview recalculates the pixel dimensions and redraws the image.
4. Make sure the unit next to Resolution reads pixels/inch, then type 300 (or whatever you were asked for). Width and Height in inches update to show the new print size.
5. Click OK, then File → Save. To keep the original, use File → Duplicate first, or File → Export to save a copy.

Things to know about Preview:

• If Resample image was ticked by mistake, Edit → Undo before saving restores the original pixels.
• Exporting a JPEG from Preview re-compresses it. Saving a PNG does not change its pixels.
• Preview can't apply one setting to many files at once through Adjust Size in a way that keeps each image's own dimensions predictable — for folders, use sips below.

Method 2: sips in Terminal (built in, batch-friendly)

Every Mac ships with sips, a command-line image tool built on the same ImageIO framework as Preview. It rewrites the resolution without touching the pixels.

Set one file to 300 DPI and write the result to a new file:

sips -s dpiWidth 300 -s dpiHeight 300 photo.png --out photo-300dpi.png

Check what a file is set to:

sips -g dpiWidth -g dpiHeight photo.png

Change every PNG in the current folder (this overwrites the originals, so copy the folder first):

for f in *.png; do sips -s dpiWidth 300 -s dpiHeight 300 "$f"; done

We checked this on a test PNG: after the command, sips reported 300 DPI and ImageMagick confirmed the pixel data was identical to the original.

If you use ImageMagick (installed with brew install imagemagick), the equivalent is:

magick photo.png -units PixelsPerInch -density 300 photo-300dpi.png

-density only sets the resolution; it doesn't resize. We confirmed on the same test PNG that the output read 300 DPI in sips with identical pixels. The -units PixelsPerInch part matters: without it, ImageMagick may keep the file's existing unit and your 300 ends up meaning 300 per centimetre.

Things to know about sips:

• Always set both dpiWidth and dpiHeight; setting one leaves the other unchanged.
• sips also has resample options (--resampleWidth, -Z). Leave them out unless you actually want new pixel dimensions.
• For JPEGs, sips re-encodes the image when it writes the new DPI. On an 816 KB Fujifilm photo, setting 300 DPI with sips produced a 421 KB file with changed pixel data — smaller because it was recompressed, not because anything clever happened. For a photo you care about, that is a real, if subtle, quality loss. If you need the JPEG identical apart from the DPI, use Method 3, which left the same photo's pixels untouched.

Method 3: Screenify's free DPI Converter (in the browser)

Our DPI Converter runs entirely in your browser — the image is never uploaded — and it is built for the question people usually have before they change anything: what is this file set to, and how big will it print?

1. Open the DPI Converter and drop in a PNG, JPEG or WebP.
2. Read the DPI now line. It shows where the value came from — the PNG pHYs chunk, the JPEG JFIF header, or the EXIF data a camera wrote — or says "Not set" when the file carries no DPI (apps then assume 72).
3. Pick 300, another preset, or type a custom value. The Prints at line shows the new size in inches and centimetres.
4. Keep the mode on Keep pixels and click Download image.

What it does differently from the first two methods:

• No re-encoding in Keep pixels mode. It edits the resolution fields in place, so a JPEG isn't recompressed and camera metadata, dates and location are left as they were.
• It updates every copy of the DPI. Camera and phone JPEGs often store DPI only in EXIF, and some files have both EXIF and JFIF values. The tool rewrites both and adds a JFIF header when there is none, so every app reads the same number. We tested a Fujifilm photo that stored 72 DPI only in EXIF: after conversion, both sips and ImageMagick read 300.
• WebP works. WebP has no DPI field, so a WebP is saved as a lossless PNG with the DPI you chose.
• Optional "Keep print size" mode resizes the image so it prints at the same inches at the new DPI — useful when layout software sizes placed images by their DPI.

Method 4: Photoshop or GIMP

If the image is already open in an editor, change DPI there.

Photoshop:

1. Image → Image Size…
2. Untick Resample.
3. Set Resolution to 300 Pixels/Inch. Width and Height in inches change; the pixel dimensions don't.
4. Click OK and save.

GIMP (free):

1. Image → Print Size…
2. Set X resolution and Y resolution to 300 pixels/in (keep the chain link closed so they match).
3. Click OK, then File → Export As…. GIMP's Print Size dialog never resamples, so the pixels are safe.

For batches in Photoshop, record the Image Size step as an action and run it with File → Automate → Batch.

Keep pixels vs. resample: which one you need

Resampling up (for example, taking a 1200 × 900 image from 72 to 300 DPI while keeping its print size, which makes it 5000 × 3750 pixels) interpolates new pixels from existing ones. The file becomes larger and the edges smoother, but no new detail appears. AI upscalers can invent plausible detail, but that is a different tool for a different job.

Common mistakes

Leaving Resample on. In Preview and Photoshop, a ticked Resample box turns "change the DPI" into "resize the image". Afterwards the DPI is right but the pixel dimensions changed, which is either a quality loss (shrinking) or an empty size gain (enlarging). Always look at the pixel Width and Height before clicking OK; they should not move.

Changing only one axis. sips -s dpiWidth 300 on its own leaves the height at its old value. Some layout apps then stretch the image when they place it. Set both.

Re-saving a JPEG over and over. Each save from Preview or sips re-encodes a JPEG and throws away a little more detail. Change the DPI once, from the best copy you have. Tools that edit the metadata in place avoid the problem.

Treating 300 DPI as a quality setting for the web. A banner or social image at 300 DPI looks exactly like the same pixels at 72 DPI, because screens don't read the number. If a web image looks soft, it needs more pixels or less compression.

Upscaling a tiny image to "make" 300 DPI. Keeping a 600-pixel-wide logo at 8 inches by resampling it to 2400 pixels produces a bigger file that still looks like a 600-pixel logo. Ask for the original artwork or a vector file (SVG, PDF) instead.

Troubleshooting

Preview still shows 72 after I saved

You probably changed the value with Resample image ticked, which resized the image instead, or you closed the dialog without saving. Reopen Tools → Adjust Size…, confirm the Resolution field, then File → Save. You can confirm from Terminal with sips -g dpiWidth yourfile.png.

Another app shows a different DPI from Preview

JPEGs can carry DPI in two places — EXIF and JFIF — and different apps read different ones. Tools that update only one leave the other behind. Run the file through the DPI Converter, which rewrites both, or check both values with exiftool if you have it installed.

GIMP or ImageMagick says 118 pixels per centimetre

That is 300 DPI. PNG stores resolution per metre, and some apps display it in centimetres: 300 ÷ 2.54 = 118.11.

The print came out blurry even though the file says 300 DPI

The label was changed on an image without enough pixels for that print size. Check the pixel table above: a 4 × 6 inch print at 300 DPI needs 1200 × 1800 pixels. If the image is smaller, the printer had to enlarge it.

My iPhone photo is a HEIC file

Most DPI tools, including ours, don't read HEIC. In Preview, choose File → Export…, pick JPEG as the format, then change the DPI of the exported copy.

Word or Google Docs inserts the image at the wrong size

Some document apps use the DPI to decide the initial size of an inserted image. Set the DPI to the value that gives the physical width you want (width in pixels ÷ desired inches), or simply resize the image after inserting it.

FAQ

Does changing DPI reduce image quality?

Not when resampling is off. The pixel data stays the same; only a number in the file changes. Quality only changes when the image is resampled (resized) or re-saved as a JPEG.

What DPI should a screenshot be?

It doesn't matter for screen use — screenshots are displayed by their pixel dimensions. For print, apply the same rule as any image: check its pixels against the print size you need.

Is DPI the same as PPI?

Strictly, PPI (pixels per inch) describes the image and DPI (dots per inch) describes a printer's ink dots. In everyday use, and in most software dialogs, "DPI" means the image's pixels per inch — the value these methods change.

Why do images default to 72 DPI?

72 DPI is a long-standing default from early Mac displays, and most software still assumes it when a file carries no resolution. It says nothing about the image's quality.

Can I change DPI on many images at once?

Yes. sips in Terminal handles a whole folder with one line (Method 2), and Photoshop can batch an action. Preview and browser tools are one image at a time.

Does DPI affect file size?

Barely. Changing the value adds or rewrites a few bytes of metadata. In our tests the files grew by 0 to 21 bytes. File size only changes meaningfully if the image is resampled.

Do websites care about DPI?

No. Browsers display images by pixel dimensions and CSS size. A 1200-pixel-wide image looks identical on a web page at 72 or 300 DPI.

Related

• Free DPI Converter — check and change DPI in your browser
• All free tools — GIF compressor, GIF to MP4 and more, all running on your device