Setting a file's DPI tag from 72 to 300 in an editor and believing the image is now print ready, when no pixels were added.
DPI
Also called dots per inch, print dpi or 300 dpi. Here is what it means, when it changes what you export, and what people get wrong.
PrintRuns on your deviceUpdated 10 August 2026
The short answer
DPI means dots per inch: the number of ink dots a printer lays down across an inch of paper. It describes a printing device, not an image file. What people usually mean is PPI, pixels per inch, which is how many image pixels land in each inch at a chosen print size.
Updated
The short version
DPI at a glance
| Quick fact | Detail |
|---|---|
| DPI measures | Ink dots a printer places per inch |
| PPI measures | Image pixels per inch at a print size |
| In the file | A metadata tag only, no effect on pixels |
| Photo print standard | 300 PPI at final size |
| Formula | Pixels needed = inches multiplied by PPI |
| Large format | 150 PPI or less is normal at distance |
Slide the table sideways to see every column.
What is the real difference between DPI and PPI?
They measure different things at different stages, and using one word for both is why so much print advice is confused.
DPI is a property of a printer. An inkjet builds colour by spraying many tiny dots of cyan, magenta, yellow and black in a halftone pattern. It needs a cluster of those dots to reproduce the colour and tone of a single image pixel, which is why a printer rated at 1200 or 2400 dpi is not printing anything like that many pixels per inch. The device figure and the image figure are not the same currency.
PPI is a property of an image at a stated size. It is arithmetic: pixels divided by inches. A 3000 pixel wide image printed 10 inches wide is 300 PPI. Printed 20 inches wide, the same file is 150 PPI. Nothing about the file changed, only the size you asked for.
So a digital image has no inherent DPI. It has a pixel width, a pixel height, and a number in its metadata that suggests a default physical size. When a printer asks for 300 DPI, they are asking for 300 PPI at your final print size, and that is a request about resolution, not about a setting you can flip.
Why does changing the DPI field do nothing on screen?
The value stored in a file, in the JFIF density fields of a JPEG, the pHYs chunk of a PNG, or the EXIF resolution tags, is metadata. It does not touch a single pixel. Its only job is to tell layout and print software what physical size to place the image at by default. Change it from 72 to 300 without resampling and your file is exactly as detailed as before, it will just drop into a page layout smaller.
This is the source of the persistent "web images are 72 DPI" myth. Browsers ignore the field completely and lay out images by pixel count and CSS. Screens have their own physical pixel density which has nothing to do with a number inside your file. If a website or a client asks for 72 DPI, what they need is the right pixel dimensions.
The one time the field matters is when you hand a file to a designer or a print shop who will place it in a document. Setting it correctly means the image lands at the intended physical size instead of needing to be scaled by hand.
How many pixels do you need to print?
Multiply your print size in inches by the PPI you are targeting. For photographic printing viewed at arm's length, 300 PPI is the working convention.
- 4 x 6 inch print at 300 PPI needs 1200 x 1800 px
- 5 x 7 inch print at 300 PPI needs 1500 x 2100 px
- 8 x 10 inch print at 300 PPI needs 2400 x 3000 px
- A4, roughly 8.27 x 11.69 inches, at 300 PPI needs about 2480 x 3508 px
- 2 x 2 inch passport photo at 300 PPI needs 600 x 600 px
That last line explains a spec people often meet without understanding it: the US State Department's photo tool requires a minimum of 600 x 600 pixels, which is exactly a 2 x 2 inch print at 300 PPI. Photomop's passport photo tool works to that pixel target for the same reason.
Work down from 300 as viewing distance grows. Posters and banners are routinely printed at 150 PPI or considerably less, because nobody presses their face to a billboard. Going the other way rarely helps: printing above about 300 PPI usually gives no visible improvement, since the halftone screen cannot resolve the extra detail.
What people get wrong about dpi
Each one is a real failure mode, not a style preference.
Quoting a resolution as a DPI number with no print size attached, which makes it meaningless.
Exporting web images at 72 DPI to save weight, when the field has no effect on file size or on how browsers display them.
Upscaling a small file to reach 300 PPI at a large print size, which invents detail rather than recovering it.
Questions people ask
DPI, answered
The follow-up questions people search for once they have the definition.
How do I change an image to 300 DPI?
Decide the print size first, then make sure the file has enough pixels: inches multiplied by 300. If it does, set the resolution field to 300 without resampling. If it does not, you need a larger original, since changing the tag alone adds no detail.
Is 72 DPI enough for the web?
The question does not apply. Browsers ignore the resolution field entirely and lay images out by pixel dimensions. What matters online is having enough pixels for the display size, including on high density screens, not what the metadata says.
What DPI do I need for a passport photo?
Think in pixels. A US passport photo is 2 x 2 inches, which at 300 PPI is 600 x 600 pixels, and the State Department's photo tool requires at least 600 x 600. Meeting that pixel count matters more than the number in the metadata.
Can I print a phone photo at poster size?
Often yes, because posters are viewed from further away and are commonly printed well below 300 PPI. A 12 megapixel photo is roughly 4000 x 3000 pixels, which is around 150 PPI at 27 x 20 inches. Check with your printer before committing.
Same cluster
More from the glossary
Neighbouring entries, so every term in the set is one hop from every other.
EXIF
EXIF (Exchangeable Image File Format) is the block of information a camera writes inside a photo file: shutter speed, aperture, ISO, lens, date and time, orientation, colour space and often GPS coordinates.
Downsampling
Downsampling is reducing an image's pixel dimensions, for example turning a 4000 x 4000 photo into 1000 x 1000.
Exposure
Exposure is how much light your camera lets reach the sensor, which decides whether a photo comes out dark, bright or just right.
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Sources
Where the facts on this page come from. Every link opens the specification, standard or documentation the claim was read at.
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