Image DPI Checker & Changer

What is image DPI?

DPI stands for dots per inch. For digital images the more accurate term is PPI, pixels per inch, but the two are used interchangeably. It is a small number stored inside the image file that tells printers and layout software how many of the image's pixels should fit into one inch of paper. A photo marked as 300 DPI asks to be printed with 300 pixels packed into every inch.

On screen this number is largely ignored. Your monitor simply shows the pixels, so a 1200x1200 image looks the same whether it says 72 DPI or 300 DPI. The value only starts to matter when the image is placed in a document or sent to a printer.

Does changing DPI improve image quality?

No. Changing the DPI value only rewrites that small piece of metadata. A 1200x1200 pixel image is still 1200x1200 pixels afterwards, with exactly the same detail. What changes is the size it will print at: the same pixels are spread over a smaller area at a higher DPI, or a larger area at a lower one.

If an image looks soft or blocky when printed, raising its DPI number will not fix that. The only way to get more real detail is to start from a larger, higher quality original.

What does 300 DPI mean?

300 DPI is a widely used guideline for printed material viewed up close, such as photos, brochures and magazines. At that density the individual pixels are too small for most people to notice at reading distance. Print shops often ask for 300 DPI files for this reason.

It is a guideline rather than a rule. Posters and banners viewed from a few metres away can look perfectly fine at 150 DPI or less, while some fine art printing benefits from more. What really matters is having enough pixels for the size you want to print.

DPI vs pixel dimensions

Pixel dimensions are the real resolution of an image: the number of pixels across and down. They decide how much detail the file actually holds. DPI is only an instruction about physical size. Two files with the same pixel dimensions contain the same detail, even if one says 72 DPI and the other says 300 DPI.

If you need more or fewer pixels, for example to make a file smaller for a website, you need to resize the image rather than change its DPI. The Image Resizer does that, the Image Compressor reduces file size, and the Image Converter switches between formats such as WebP and PNG.

How print size is calculated

Print size is simply the pixel dimensions divided by the DPI. A 3000x2400 pixel image at 300 DPI prints at 10x8 inches, which is about 25.4x20.32 cm. Set the same image to 150 DPI and it prints at 20x16 inches, with each pixel twice as large. This tool does that calculation for you as soon as you pick a value.

Which formats are supported?

JPG, PNG and BMP files can be checked and changed. The new value is written into the file header without re-encoding the image, so the pixels stay exactly as they were, and the result is read back to confirm the change before you download it. WebP files can be checked when they contain resolution information, but WebP has no dependable place to store DPI, so changing it is not offered for that format. Everything happens in your browser and your images are never uploaded.