How to Check Image DPI and PPI, and What They Mean
By Akmal Ali · Published · Updated · 5 min read
Check the DPI with a DPI checker, in File Properties › Details on Windows, or in Preview’s Inspector on a Mac. The stored DPI is only a print setting: what decides quality is the number of pixels. Divide the pixels by the print size in inches to get the real PPI, and aim for about 300 for photo prints.
A print shop asks for “300 DPI”. An application form wants a photo “at 200 DPI”. Your image says 72 DPI and you worry it’s low quality. Most of this confusion comes from one fact: the DPI number stored in an image file is a print setting, not a measure of quality. What decides quality is the number of pixels.
What is the difference between DPI and PPI?
| PPI (pixels per inch) | DPI (dots per inch) | |
|---|---|---|
| Describes | How densely an image’s pixels are printed or shown | How many ink dots a printer places per inch |
| Belongs to | The image, or a screen | The printer |
| Typical values | 72–600 for images; about 90–500 for screens | 300–2400 and more for printers |
A printer needs several ink dots to reproduce the colour of one pixel, so DPI and PPI are different things. But image files, Windows, Photoshop and most forms say “DPI” when they mean the pixels-per-inch value stored in the image. In this guide, and in practice, the two words mean that stored value.
Why do pixels matter more than DPI?
An image is a grid of pixels. The DPI value only tells a printer how large to print that grid by default. Take a 3000 × 2000 pixel photo:
- At 300 DPI, it prints at 10 × 6.67 inches.
- At 72 DPI, it prints at 41.7 × 27.8 inches.
Both files contain exactly the same detail. Changing the number from 72 to 300 doesn’t add a single pixel; it only tells the printer to pack them more tightly, which makes the default print smaller and sharper. On a screen, the stored DPI is ignored completely.
The number lives in the file’s metadata: the X and Y resolution fields of EXIF and the density fields of JFIF in a JPG, and the pHYs chunk in a PNG. Many files have none at all.
How to check the DPI of an image
In your browser
- Open the DPI / PPI checker and select a JPG, PNG, WebP or BMP image.
- Read the pixel dimensions and the resolution stored in the file. If the file stores none, it says “not found” instead of guessing.
- Use the PPI calculator below it to work out the print size, or the PPI for a size you need.
DPI / PPI Checker
See the stored DPI, the pixel size and the print size at 72, 150 and 300 PPI, or work out the PPI for any print.
On Windows
Right-click the file, choose Properties, open the Details tab and look for Horizontal resolution and Vertical resolution under Image.
On a Mac
Open the image in Preview, choose Tools › Show Inspector, and read Image DPI on the General Info tab.
Be careful with these numbers.
How to calculate PPI for a print
PPI = pixels ÷ print size in inches
Print size in inches = pixels ÷ PPI (multiply by 2.54 for centimetres)
Example: a phone photo of 4032 × 3024 pixels printed at 300 PPI is 4032 ÷ 300 = 13.44 inches wide and 3024 ÷ 300 = 10.08 inches tall. Printed at 10 × 7.5 inches instead, it has 403 PPI, more than enough.
To go the other way, multiply the print size by the PPI. These are the pixels you need for common print sizes:
| Print size | At 300 PPI | At 150 PPI |
|---|---|---|
| 6 × 4 in (10 × 15 cm) | 1800 × 1200 | 900 × 600 |
| 7 × 5 in | 2100 × 1500 | 1050 × 750 |
| 10 × 8 in | 3000 × 2400 | 1500 × 1200 |
| A4 (210 × 297 mm) | 2480 × 3508 | 1240 × 1754 |
| A3 (297 × 420 mm) | 3508 × 4961 | 1754 × 2480 |
What PPI do you need?
- About 300 PPI for photos and documents viewed at arm’s length: prints, brochures, photo books.
- 150–200 PPI usually still looks good for larger prints viewed from a little further away.
- Less than 150 PPI can be fine for posters and banners seen from across a room.
These are rules of thumb. When a printer gives a figure, use theirs.
What about screens?
Screens have a PPI too, fixed by their size and resolution. A 27-inch monitor with 2560 × 1440 pixels has about 109 PPI: the diagonal in pixels, √(2560² + 1440²) ≈ 2937, divided by 27 inches. Phones are often above 400 PPI. None of this depends on the image’s DPI value; a 1200-pixel-wide image covers 1200 screen pixels, before any scaling by the device.
Common misconceptions
- “72 DPI means web quality.” 72 is an old default dating from early Mac screens. It says nothing about how detailed the image is.
- “Changing the DPI to 300 improves quality.” Without adding pixels, it only changes the default print size. Adding pixels by enlarging can’t create real detail either.
- “A form wants 300 DPI, so the file must say 300.” Usually the form really wants a pixel size. “3.5 × 4.5 cm at 300 DPI” means 413 × 531 pixels. Check the size you have with the image dimensions checker, resize with the image resizer, and you’re done; see how to resize without distorting the image.
- “DPI is lost when I convert or compress.” Often true, and harmless. Many programs don’t copy the value when they save a new file, and printers then use their own default. The pixels are unchanged.
If you do need to change the stored value
Some print workflows check the number itself. Image editors can change it without touching the pixels: in Photoshop, open Image › Image Size, untick Resample and enter the new resolution; in GIMP, use Image › Print Size. The DPI / PPI checker only reads the value, and never changes your file.
Frequently Asked Questions
Why does Windows show 96 DPI?
96 is the standard Windows screen setting, and some programs show it when a file stores no value of its own. It says nothing about the image; check the pixel dimensions instead.
Why does my scanner save at 600 DPI?
For a scan, the number is real: the scanner sampled 600 points per inch of paper, so an A4 page at 600 DPI is about 4961 × 7016 pixels. 300 DPI is plenty for documents you will read on screen or print at the same size.
What DPI should a scanned document be for an online form?
Usually 150 to 300 DPI. Around 200 keeps normal text readable while keeping the file small. Check whether the form also sets a file size, and compress the scan if it does.