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What Is DPI? DPI vs PPI, How to Check a Photo's DPI, and the Pixels Every Print Size Needs

By Ayush Patnaik, founder of AccioPix

Published October 24, 2026 · 12 min read

DPI means dots per inch. It is how closely a printer puts down ink. For a photo, what matters is PPI, pixels per inch. That is the pixels you have, divided by the inches you print. A 300 DPI tag on its own means nothing. A 4 × 6 inch print needs 1,200 × 1,800 pixels to reach 300 PPI, whatever the file label says.

This guide shows how to check a photo's DPI on Windows, Mac, iPhone and Android. It gives the pixel counts for common photo print sizes. It also covers what to do when a file falls short. (Mouse DPI is a different thing. It measures how far the pointer moves. This post is about pictures.)

DPI and PPI, defined

DPI is how many dots of ink a printer puts on one inch of paper. PPI is how many pixels of a photo fall into that same inch. Adobe's guide to pixel density says the same thing: "You can think of DPI as the print output, and PPI as the digital input." (Adobe, PPI and pixel density.)

The two numbers live on different scales. For its SureColor SC-P700 photo printer, Epson quotes a printing resolution of 5,760 × 1,440 DPI. If you feed it an image at 300 PPI, each pixel covers about 19 droplet positions across (5,760 ÷ 300 = 19.2). That printer's DPI describes the hardware. It says nothing about your file.

In practice, people now say DPI when they mean PPI. Labs use the term, software uses it, and so does the headline of this post. Pro Lab, a print and photo book lab in India, defines DPI in its file guide as "a measure of how much detail an image has at its final print size" (Pro Lab, file resolution requirements). That is PPI by another name. When a lab asks for 300 DPI, it wants 300 of your pixels on each inch of paper.

The number written into the file is a third item: a tag. The Exif standard used by cameras states that "when the image resolution is unknown, 72 [dpi] shall be designated" (CIPA DC-008, Exif 3.0). This is why so many files show 72. No one picked it. It is just the default.

300 DPI without pixel dimensions

300 DPI without pixel dimensions means nothing to a lab. The tag is one number stored next to the pixels. You can change it without touching them. We checked this on a 6,000 × 4,000 JPEG straight from a Nikon D3400. The camera had tagged it 300 DPI. We edited the tag to 72. Four bytes of an 11.6 MB file changed. Decoded, the two files match, pixel for pixel.

Still, the two files state different sizes. Size is pixels divided by DPI: 6,000 ÷ 300 = 20 inches wide, and 6,000 ÷ 72 = 83.3 inches wide. Neither claim binds anyone. A lab prints on the paper you choose. Order an 8 × 12 from either file and both yield 500 pixels per inch (6,000 ÷ 12 and 4,000 ÷ 8). You get the same print.

Photoshop and Preview both let you change the number without changing the pixels. Adobe's resolution guide says to "deselect Resample" for exactly this (Adobe, image resolution). Apple's Preview guide says the same in its own words: deselect "Resample image" before changing the width or height, and no detail is lost (Apple, resize an image in Preview). With Resample on, the software adds or throws away pixels instead. That is a different job, called resampling.

The phrase "300 DPI" makes sense only as a pair: pixels and inches. A 4 × 6 at 300 takes 1,200 × 1,800 pixels. Asking for 300 DPI without a print size is half a sentence.

Checking a photo's DPI on Windows, Mac, iPhone and Android

The way you check the DPI of an image depends on your device. A computer shows you the tag as well as the pixel dimensions. A phone shows you only the pixel dimensions. That is the number a lab needs anyway.

• Windows: right-click the file and select Properties. Open the Details tab. Look under Image. You will find Dimensions, Width and Height in pixels, and Horizontal resolution and Vertical resolution in dpi. The Microsoft property reference defines horizontal resolution as "the number of pixels per resolution unit in the image width" (Microsoft Learn).
• Mac, in Preview: open the photo. Click Tools, then Adjust Size. The box gives the width, height, and Resolution. Change the units to pixels to find the pixel dimensions. Keep "Resample image" unticked if you only want to look. In Finder, Get Info also displays Dimensions under More Info, as Pro Lab's guide notes.
• Mac, in Terminal: sips -g dpiWidth -g pixelWidth -g pixelHeight photo.jpg shows the tag and the pixels on one line. It uses the image tool that comes with macOS.
• Photoshop: open Image, then Image Size. Check Resolution with Pixels/Inch set, as Adobe's DPI guide explains.
• iPhone: open the picture in Photos and swipe up, or tap the Info button. Apple displays "camera metadata such as lens, shutter speed, file size, and more" in that view (Apple, photo information on iPhone). Pro Lab's guide recommends this swipe, on iPhone and Android, for reading a photo's dimensions. There is no DPI, because a phone photo has no print size until you pick one.
• Android: Open the image in Google Photos and swipe up. You will find the file data under Details (Google Photos Help). Make sure it is the original file. Google's Storage saver backup cuts any photo over 16 MP down to 16 MP.

For a whole folder, the free EXIF viewer lists each photo's pixel dimensions next to its camera, lens and exposure, in the browser. It doesn't show the DPI tag, and for printing that is the less useful number. What else sits in a file's metadata is in EXIF data: what your photos reveal.

A quick caution. The picture a guest saved from a family chat is often not the picture that was taken. In our look at WhatsApp photo compression, standard quality gave us 1,280 to 1,600 pixels on the long edge. At 300 PPI that means 4.3 to 5.3 inches (1,280 ÷ 300 and 1,600 ÷ 300). That is not quite a 6-inch print. Get the original before you order.

Photo print sizes in pixels

Photo print size in pixels is inches multiplied by PPI on each side. The table below shows these numbers at 300 PPI, the usual target, and at 150 PPI, which Pro Lab calls the practical minimum. Adobe's DPI guide also sets 300 as the benchmark photographers and designers use. I worked out the numbers myself, rounding to the nearest pixel. Pro Lab's own table matches for every size it lists.

Megapixel counts can fool you because shapes differ. A 12 MP phone photo has 4,032 × 3,024 pixels. That is a 4:3 frame. A 4 × 6 print is 3:2, so the lab cuts a strip from one side. Before you crop it, that phone photo spans 13.4 × 10.1 inches at 300 PPI (4,032 ÷ 300 and 3,024 ÷ 300).

Distance changes the target too. Adobe's guide says a poster needs "at least 100 DPI", depending on its size and how far away the viewer stands. A canvas across a hall can sit near the floor column. An album is held at arm's length, so its spreads belong in the 300 column. The page sizes albums actually come in are in wedding album sizes.

Passport photos work the other way. The prints are tiny, and the dimensions are exact. The free passport photo maker creates the single photo at 600 DPI, so a 35 × 45 mm photo comes out at 827 × 1,063 pixels. It puts print sheets together at 300, which leaves a 4 × 6 sheet at exactly 1,800 × 1,200 pixels. Have the shop print it as 4 × 6 with no "fit to page" scaling, or the photos shrink off spec.

A worked example: one wedding frame, three outputs

An example shows how much one camera file can do. Consider the 24-megapixel Nikon frame from above, measuring 6,000 × 4,000 pixels.

1. A 4 × 6 print for grandparents. That gives 6,000 ÷ 6 = 1,000 pixels per inch. This is more than three times the 300 target. The lab just scales it down.
2. A full-bleed album spread. Two 12 × 12 pages make 24 × 12 inches. You crop the frame to 6,000 × 3,000 to match the shape, giving 6,000 ÷ 24 = 250 PPI. That sits between Pro Lab's 150 floor and its 300 target. It looks fine at arm's length. Across a 36-inch spread, it falls to 6,000 ÷ 36 = 167 PPI, just above the floor. That picture looks better on one page than across two.
3. Every guest's phone. Here DPI doesn't enter into it. AccioPix keeps uploads at full resolution, and each guest who sends a selfie on WhatsApp gets the full-size files they appear in. Anyone who wants a print already has a file that clears the table. At ₹0.20 per photo, a 500-photo wedding costs about ₹100 to deliver; the rest is on the pricing page.

That third line is what saves the photographer's evenings. Fewer people ask for "the full-size one, for printing" when every guest has it already. The AccioPix page for photographers shows how your name travels with the album.

Upscaling a photo that falls short

Upscaling a photo adds pixels. When a file falls short of the table, this is your only fix besides printing smaller. Ordinary resampling, the Resample box in Photoshop or Preview, builds each new pixel from its neighbours. Enlarge too much and edges turn soft.

An AI upscaler guesses the detail instead. Our free image upscaler uses a SPAN network. Wan and colleagues call it a "highly efficient SISR model that balances parameter count, inference speed, and image quality" (Wan et al., 2023). SISR means single-image super-resolution: one small photo in, one larger photo out. You choose 2x or 4x. The film above turns a 300 × 400 portrait into 1,200 × 1,600, enough for a print of 4 × 5.3 inches at 300 PPI (1,200 ÷ 300 and 1,600 ÷ 300).

The work happens in your browser. It runs on your graphics chip if allowed, and on the slower processor if not. The photo is never uploaded. An ordinary computer can make up to about 64 megapixels, a phone less. Very large originals are upscaled 2x instead of 4x, and the tool tells you.

Know what it can't do. An upscaler paints plausible detail. It cannot rescue a face that was never sharp. On a heavily compressed file, it sharpens the compression blocks too. Pro Lab's guide is blunt about this limit: "No printing process can fully restore detail that wasn't in the original file." So the order is: find the original, print smaller, then upscale. For a photo with enough pixels that looks soft or grainy, the photo enhancer runs the same engine at the same size, cleaning and sharpening without enlarging. Out-of-focus shots are a different issue, treated in how to unblur a photo.

Frequently asked questions

What is DPI?

DPI stands for dots per inch. That is how many dots of ink a printer drops on one inch of paper. People also use the term, loosely, to mean pixels per inch at a set print size. When a lab asks for 300 DPI, it wants 300 of your pixels for every inch of the print.

What is PPI?

PPI stands for pixels per inch. For a print, divide the photo's width in pixels by the print's width in inches. A 6,000-pixel-wide photo printed 20 inches wide gives 300 PPI. At 40 inches wide, it gives 150. PPI also describes how sharp a screen is.

How do I check the DPI of an image?

On Windows, right-click the file, pick Properties, and open the Details tab. On a Mac, open it in Preview, go to Tools, and choose Adjust Size. A phone shows pixel dimensions instead, and that is what a lab wants. Divide the pixels by the print size in inches to find the real figure.

What is 300 DPI?

300 DPI is the usual target for a sharp photo print. It means 300 pixels on every inch of paper. By itself, it tells you nothing about size. A 4 x 6 inch print at 300 DPI takes 1,200 x 1,800 pixels. An 8 x 10 needs 2,400 x 3,000.

How do I change the DPI of an image?

In Photoshop, open Image Size, untick Resample and type in the new resolution. In Preview on a Mac, click Tools, then Adjust Size, untick Resample image and do the same. The pixel count doesn't change, so the print doesn't get any sharper. To get more pixels, you have to upscale.

What resolution do I need for a 4x6 print?

You need 1,200 x 1,800 pixels for a sharp print at 300 pixels per inch. Pro Lab, for one, accepts a floor of 600 x 900, at 150 pixels per inch. A 12 MP phone photo, at 4,032 x 3,024, clears both. A photo saved from WhatsApp in standard quality might not.

References

• Adobe, Pixels per inch (PPI) and pixel density. Read 24 October 2026.
• Adobe, DPI meaning. Read 24 October 2026.
• Adobe, What does resolution mean? Image resolution guide. Read 24 October 2026.
• Apple Support, Crop, resize, or rotate an image in Preview on Mac. Read 24 October 2026.
• Apple Support, See photo and video information on iPhone. Read 24 October 2026.
• CIPA, CIPA DC-008-Translation-2024: Exchangeable image file format for digital still cameras, Exif Version 3.0. Published May 2023, corrected December 2024. Section 4.6.5.1.8, XResolution.
• Epson UK, SureColor SC-P700 specifications. Read 24 October 2026.
• Google Photos Help, Choose the backup quality of your photos and videos (Android). Read 24 October 2026.
• Microsoft Learn, System.Image.HorizontalResolution. Read 24 October 2026.
• Pro Lab Help Centre, File resolution and quality requirements: DPI, pixels and print quality, last updated 31 May 2026. Read 24 October 2026.
• Wan, C., Yu, H., Li, Z., Chen, Y., Zou, Y., Liu, Y., Yin, X. and Zuo, K., 2023. Swift parameter-free attention network for efficient super-resolution. arXiv:2311.12770.