Mouse DPI Measurement & Sensor Calibration Checker

What Is DPI in an Image?

DPI stands for dots per inch. For an image file, it is a resolution setting stored in the metadata. It says how many of the image’s pixels should be placed in each inch of paper. A photo 3000 pixels wide set to 300 DPI prints 10 inches wide. Set it to 100 DPI and the same file prints 30 inches wide with bigger, softer-looking pixels.

The setting lives in different places depending on the format. JPEG files can store it in up to three places: the JFIF header, the EXIF data written by cameras and editors, and a Photoshop resource block. PNG uses a pHYs chunk measured in pixels per metre (300 DPI is stored as 11,811). TIFF, BMP and the EXIF block in WebP and HEIC have their own fields. The checker reads all of them and tells you which one it found, because apps don’t always read the same one.

A screen ignores this setting completely. A 3000-pixel image looks the same on a monitor whether it says 72 or 300 DPI. DPI only matters when the image is printed or placed into a document with a physical size, such as a Word file, an InDesign layout or a PDF.

How to Check the DPI of an Image

1. Add the image above. Drag it in, paste a screenshot, or choose one or more files. JPG, PNG, TIFF, WebP, BMP, GIF, HEIC and AVIF are supported.
2. Read the saved DPI at the top, along with where it came from. If a JPEG stores different values in different places, you’ll see a warning with each value.
3. Check the pixel size and megapixels. This is what actually decides how large the image can print.
4. Pick your print size in the print check. The tool shows the effective PPI, a quality rating and the pixels needed for a true 300 PPI print.
5. Change the DPI if a printer or form asks for a specific value. The download is identical except for the DPI label.

Checking several images at once? Add them together. The All images table compares their pixels, saved DPI and quality at your chosen print size, which helps when choosing photos for an album or checking a batch of product shots.

DPI vs. PPI: What Is the Difference?

The number inside an image file is strictly PPI, but Windows, Photoshop exports, print shops and upload forms almost all call it DPI, so this page does too. The two are not the same thing. An inkjet printer uses many tiny ink dots, mixing cyan, magenta, yellow and black, to reproduce each pixel. That is why a 5760 DPI printer still needs only a 240–300 PPI image. Sending more pixels than that usually makes no visible difference.

How to Check Image DPI Before Printing

1. Know the final print size, including any crop. A 4 × 6 photo and an A4 page need very different pixel counts.
2. Check the effective PPI at that size, not just the saved DPI. Aim for 300 for photos and text, 240+ for most prints, and 150+ for posters.
3. Check the shape. A 3:2 camera photo on 8 × 10 paper is either cropped or left with white borders. The print check shows how much.
4. Check the colour mode. Home printers and photo labs expect RGB (usually sRGB). Offset printers often want CMYK PDFs. The checker shows the colour mode and embedded profile.
5. Use the original file. Images saved from WhatsApp, Facebook or a website are usually shrunk and compressed. The megapixel count shows this quickly.
6. Only then set the DPI, if a print shop asks for “300 DPI” files. With enough pixels, relabelling is all they need.

How to Check if an Image Is 300 DPI

Printers and forms say “300 DPI” but usually mean “sharp enough at the size we print it.” That is a question of pixels:

A 2400 × 3000 pixel image is a true 300 PPI at 8 × 10 inches, even if its metadata says 72. A 1200 × 1800 image saved as “300 DPI” is only 300 PPI up to 4 × 6 inches. At 8 × 10 it drops to 150. So check both: the saved DPI shown at the top of the checker, and the effective PPI in the print check. If a strict print shop rejects a file for its label, use Change DPI to set 300 without changing the image.

Image DPI vs. Pixel Dimensions

Pixel dimensions (for example 4032 × 3024) are the real amount of detail in an image. DPI is a note about how to spread that detail across paper. That’s why two files with the same pixels but different DPI look identical on screen and can print identically if you choose the same paper size.

How DPI Affects Image Print Size

With the pixels fixed, DPI and print size move in opposite directions. Double the DPI and the print size halves. The same 3000 × 2000 image prints at:

• 72 DPI: 41.7 × 27.8 in (105.8 × 70.6 cm), large but visibly soft up close;
• 150 DPI: 20 × 13.3 in (50.8 × 33.9 cm), good for a poster;
• 240 DPI: 12.5 × 8.3 in (31.8 × 21.2 cm), very good;
• 300 DPI: 10 × 6.7 in (25.4 × 16.9 cm), sharp enough to hold in the hand.

In practice the saved DPI only sets the default size. When you choose “8 × 10” in a print dialog or photo-lab order, the software scales the pixels to fit, and the saved DPI is ignored. It matters most when an image is placed into Word, InDesign, Canva or a PDF, where it appears at its “native” size until you resize it.

How to Calculate Print Size From DPI and Pixels

Example: 4032 px ÷ 300 = 13.44 inches (34.1 cm). Pixels needed for common sizes at 300 PPI:

The quick calculator above does this for any pixel size, and the print check does it for your actual file, including cropping when the shapes differ.

What Does 72 DPI, 150 DPI and 300 DPI Mean?

Why do posters get away with less? Your eye resolves roughly one arcminute. At a distance d in inches, that is about 3,438 ÷ d pixels per inch. That works out to ≈ 286 PPI at 12 in (reading distance), ≈ 143 PPI at 2 ft and only ≈ 48 PPI at 6 ft. The viewing-distance slider in the checker uses this rule.

Why an Image May Have No DPI Metadata

• Screenshots on many systems are saved as PNG without a pHYs chunk.
• Web exports (“Save for Web”, image optimisers, CMS resizing) strip metadata to save bytes.
• Social media and chat apps (WhatsApp, Instagram, Facebook, Telegram) re-encode uploads and remove most metadata.
• AI image generators and canvas exports usually write plain PNG, WebP or JPEG with no resolution set.
• Some JPEGs store only an aspect ratio (JFIF “units 0”), which isn’t a DPI.

When no DPI is saved, programs make it up. Photoshop and many Mac apps assume 72, and many Windows apps assume 96. None of this changes the image. A 4000-pixel image with no DPI still has 4000 pixels. If a system insists on a value, set one with the tool.

Does Changing DPI Increase Image Quality?

No. Changing the DPI value, which Photoshop calls resizing without resampling, only changes the label and the default print size. The pixels are untouched. The checker’s Change DPI download proves it: the new file has exactly the same pixel dimensions, and only the resolution fields change.

Changing the pixel count, called resampling or upscaling, is different. It invents new pixels between the existing ones. Standard upscaling (bicubic) makes a larger file that looks smoother, not more detailed. AI upscalers can add convincing detail for moderate enlargements, perhaps 2×, but they guess rather than recover real information. When a print is too soft, the best fixes are, in order: use the original or a higher-resolution file, print smaller, then upscale carefully.

How to Check DPI on Windows, Mac, iPhone and Android

Common Image DPI Problems Before Printing

Free DPI Checker FAQs

Resources and Sources

• W3C PNG SpecificationDefines the pHYs chunk that stores PNG resolution in pixels per metre.
• CIPA Exif 2.32 StandardXResolution, YResolution and ResolutionUnit tags used by cameras.
• Adobe: Image size and resolutionHow Photoshop changes resolution with and without resampling.
• Adobe: How resizing affects resolutionPixel dimensions, document size and resolution explained.
• Apple: Image information in PreviewUsing the Inspector in Preview on Mac.
• Microsoft Q&A: DPI in Windows ExplorerFinding horizontal and vertical resolution in file properties.
• Library of Congress: Exif formatBackground on how Exif metadata is stored in images.
• Resizing vs. resamplingPhotoshop Essentials: why changing DPI alone doesn’t add detail.

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Last reviewed: September 2026.