DPI to PPI Converter
What an image prints at, what resolution a size needs, and why a 1200 dpi printer wants a 150 ppi file rather than a 1200 ppi one.
Image 4,000 × 3,000 pixels
megapixels 12.00
uncompressed, 24-bit 34.3 MB
At 300 ppi it prints
inches 13.33 × 10.00
centimetres 33.87 × 25.40
millimetres 338.7 × 254.0
Printed 20.00 in wide
resolution you get 200 ppi
pixels needed for 300 ppi 6,000
verdict fine for an office printer, short for a press
What the work needs
a newspaper, 85 lpi 170 ppi → prints 23.5 × 17.6 in
a magazine, 133 lpi 266 ppi → prints 15.0 × 11.3 in
commercial offset, 150 lpi 300 ppi → prints 13.3 × 10.0 in
fine art, 175 lpi 350 ppi → prints 11.4 × 8.6 in
a billboard, viewed far away 50 ppi → prints 80.0 × 60.0 in
A printer at 1,200 dpi
screen it can hold 75 lpi
greys per halftone cell 256
image resolution it wants 150 ppi
not 1,200 ppi, which is 8.0 times more data than it can use
On screen
in CSS pixels 4,000 × 3,000, since CSS defines an inch as 96px
at a device ratio of 2 2,000 × 1,500 CSS px, so serve this as the 2× image
on a 1080p 24-inch monitor 43.48 in wide at 92 ppi
on the CSS reference pixel 41.67 in wide at 96 ppi
on a 27-inch 4K monitor 24.54 in wide at 163 ppi
on a 13-inch MacBook Pro 17.62 in wide at 227 ppi
on an iPhone 15 8.70 in wide at 460 ppi
PPI and DPI are different measurements. PPI is pixels per inch, a
property of an image or a screen. DPI is dots of ink per inch, a
property of a printing device. A printer uses many dots to reproduce one
image pixel, so the two numbers are not interchangeable and matching
them wastes an enormous amount of disk.
At 1,200 dpi the device can hold a screen of about 75 lines per inch,
and an image at twice that, 150 ppi, gives it everything it can use.
Sending 1,200 ppi sends 8.0 times the data it can print.
"300 dpi" as a requirement for artwork means 300 ppi. It is used so
widely that arguing about it is pointless, and knowing which one is
meant matters when somebody asks for 1,200.
There is no DPI or PPI stored in a JPEG that changes the pixels. The
number in the file header is metadata: a suggestion about physical size
that some applications honour and browsers ignore entirely. Changing it
in an image editor without resampling changes nothing about the image.
A CSS pixel is neither of these. The CSS specification defines one inch
as exactly 96 CSS pixels, so `1in` in a stylesheet is 96px on every
screen and is not an inch on any modern one. Physical units in CSS are
for print stylesheets, and even there the browser decides.
The viewing distance sets the requirement. A billboard at 50 ppi looks
sharp from the road and a business card at 150 does not, because what
the eye resolves is angular. Anything past about 400 ppi is beyond what
a press can reproduce and what a reader can see.
Upscaling does not add resolution. Doubling the pixel dimensions of a
150 ppi file to claim 300 produces a file with the right numbers in the
header and the same detail, and print reproduces the softness
faithfully.
Output is valid and updates as you type.
Fix the highlighted fields to update the output.
DPI and PPI are not two names for the same thing, and the difference costs disk space and arguments with printers.
PPI is pixels per inch: a property of an image, or of a screen. DPI is dots of ink per inch: a property of a printing device. A 1,200 dpi printer uses many dots of ink to reproduce one image pixel, so it does not want a 1,200 ppi file. It wants about 150.
The bridge between them is halftone screening. A press reproduces tone as a grid of cells at some number of lines per inch, and it needs roughly sixteen times the LPI in DPI to give each cell enough greyscale steps. The image then wants 1.5 to 2 times the LPI. That is where “300 ppi for print” comes from: a 150 lpi commercial press at a quality factor of 2.
How to use
- Put in the pixel dimensions of the image.
- Set the resolution you intend to print at, or the size you want to print, and read the other.
- Put in the printer’s DPI if you want to know what resolution it can actually use.
Example
A 12-megapixel image, printed at 300 ppi, on a 1,200 dpi device:
Image 4,000 × 3,000 pixels
megapixels 12.00
uncompressed, 24-bit 34.3 MB
At 300 ppi it prints
inches 13.33 × 10.00
centimetres 33.87 × 25.40
millimetres 338.7 × 254.0
Printed 20.00 in wide
resolution you get 200 ppi
pixels needed for 300 ppi 6,000
verdict fine for an office printer, short for a press
A printer at 1,200 dpi
screen it can hold 75 lpi
greys per halftone cell 256
image resolution it wants 150 ppi
not 1,200 ppi, which is 8.0 times more data than it can useEight times the data, none of it reproducible. That is the practical consequence of treating the two numbers as interchangeable.
Pitfalls
“300 dpi artwork” means 300 ppi. The usage is so widespread that correcting it is pointless, and the distinction matters the moment somebody says 1,200.
The number in a JPEG header changes nothing about the pixels. It is metadata: a suggested physical size that some applications honour and browsers ignore completely. Changing it in an image editor without resampling changes the label and not the image.
Upscaling does not add resolution. Doubling the pixel dimensions of a 150 ppi file to claim 300 produces the right header and the same detail. Print reproduces the softness faithfully.
A CSS pixel is a third thing. The CSS specification defines one inch as exactly 96 CSS pixels,
so 1in in a stylesheet is 96px on every display and is not an inch on any modern one. Physical
units in CSS are for print stylesheets, and even there the browser has the final say.
Viewing distance sets the requirement. What the eye resolves is angular, so a billboard at 50 ppi is sharp from the road and a business card at 150 is not. Past about 400 ppi you are beyond what a press can reproduce and what a reader can see.
More dots does not mean more colours. A larger halftone cell gives more tonal steps, up to the 256 that PostScript allows, and beyond that extra device resolution buys sharper edges rather than smoother gradients.
The megabyte figure is the pixels, not the file. 4,000 × 3,000 at 24 bits is 34.3 MB in memory whatever the JPEG on disk weighs, which is the number that matters for a canvas or an editor.
Compatibility
Arithmetic in the browser: nothing is uploaded and nothing is stored. No image is read, only its dimensions.
The inch is exact: 2.54 cm, 25.4 mm, 72 points. The CSS pixel is the specified 96 to the inch rather than a measurement of anything. The halftone figures use the standard relationships, and the greyscale count is capped at 256 because that is the PostScript limit, which is where the sixteen-times rule of thumb comes from in the first place.
The screen comparisons are real densities: about 92 ppi for a 1080p 24-inch monitor, 163 for a 27-inch 4K, 227 for a 13-inch MacBook Pro, 460 for a current iPhone. They are there to show how far the CSS reference pixel has drifted from any physical screen.