DPI vs PPI: What Is the Difference?

Quick answer

PPI describes how many image pixels are assigned to an inch of physical display or print size. DPI describes printer dots per inch. People and software sometimes use the labels interchangeably, but separating source pixels from output dots prevents false assumptions about resolution.

Two density terms at different stages
Criteria	PPI	DPI
Counted element	Image pixels	Printer dots
Typical use	Image placement or display density	Printer output capability or setting
Changes pixel count?	Not by metadata alone	No

Calculate PPI at print size

Divide pixel width by intended print width in inches. A 2,400-pixel-wide image placed eight inches wide supplies 300 PPI. Place the same file sixteen inches wide and it supplies 150 PPI. No pixels disappeared; the physical placement changed their density.

The printer then represents those pixels using its dots, inks, and screening method. Several output dots may contribute to the reproduction of one source pixel, so a printer's DPI number is not a direct statement of distinct image pixels.

One image file, three print sizes

A fixed 1,800 × 1,200 pixel image demonstrates why PPI belongs to the image-plus- size relationship rather than to the file alone:

1,800 × 1,200 pixels at different physical sizes
Print size	Supplied pixel density	What changed
6 × 4 in	300 PPI	Pixels are packed most densely
9 × 6 in	200 PPI	Same pixels spread over a larger area
12 × 8 in	150 PPI	Same file, lower placement density

Metadata trap

Changing a file's resolution metadata from “72” to “300” without resampling does not create new pixels. It can change the default physical size a program suggests, but the captured pixel dimensions remain the limiting inventory.

Why the vocabulary gets mixed

The Library of Congress notes that DPI originated with print dots while PPI is the more precise digital-image term, yet common usage often blurs them. When a service requests “300 DPI artwork,” confirm whether it actually wants 300 PPI at final dimensions and ask for required pixel dimensions.

Check a real file

If you know the pixel dimensions and intended print size, the 300 DPI guide includes a calculator that reports the supplied PPI and the pixel dimensions needed for a target print density.

Working backwards: how many pixels does a print job need?

The most useful calculation reverses the first one. Multiply the intended print dimension in inches by the pixel density you want to supply. For a 10 × 8 inch print at 300 PPI, the image needs 3,000 × 2,400 pixels. For the same print at 150 PPI, which is acceptable for some large or distant-viewing uses, it needs 1,500 × 1,200 pixels. Phone cameras and most modern cameras capture far more pixels than either figure, so the practical limit is more often a heavily cropped or downloaded web image that was never large enough.

If a file falls short, enlarging it in software adds interpolated pixels rather than new detail. The result can look smoother but not sharper, so the safest fix is to start from a larger original or to reduce the print size.

Screens, scans, and printers use the terms differently

The vocabulary shifts with the device. A monitor or phone is described by pixels per inch, which tells you how finely its pixels are packed. A scanner is usually specified in samples per inch or, loosely, DPI, which sets how many samples it captures from each inch of the original. A printer's DPI describes the dots its mechanism can place. Because manufacturers and software use the terms loosely, an unlabeled number should be treated as a prompt to check what is being counted.

Web images are a special case. A browser displays an image according to its pixel dimensions and the screen's density, so a "72 DPI" or "300 DPI" tag inside a web image has no effect on how it looks online. Only the pixel width and height matter on screen.

A quick checklist before you send artwork to print

Confirm the final physical size, calculate the pixel dimensions needed from that size and the target PPI, compare them with the file, and check the colour mode and file format the printer asks for. Keep the original, unscaled image so that the file can be re-exported if the size changes. If the numbers do not meet the requirement, ask the printer what minimum density they accept rather than relying on metadata.