Image Formats and Pixel Sizes for Printing

Pixels needed for common print sizes

The formula is print size in inches multiplied by pixels per inch (ppi). 300 ppi is the usual target for photo prints viewed up close. The table applies it to common sizes.

Print size	Pixels at 300 ppi	Megapixels
4 x 6 in	1200 x 1800	2.16
8 x 10 in	2400 x 3000	7.20
A4 (210 x 297 mm)	2480 x 3508	8.70
A3 (297 x 420 mm)	3508 x 4961	17.40
16 x 20 in	4800 x 6000	28.80

Checking your own photo

Divide each pixel dimension by 300 to get the print size in inches at that density. A phone photo of 4032 by 3024 pixels gives 13.44 by 10.08 inches at 300 ppi. That is more than enough for an 8 by 10 print, and just under 14 inches on the long side.

There is one catch: aspect ratio. The phone photo is 4:3, while an 8 by 10 print is 5:4. To fill the paper you must crop. An 8 by 10 portrait print at 300 ppi needs 3000 by 2400 pixels. Cropped to 5:4, the phone photo keeps 3780 by 3024 pixels (the full 3024 pixel height and 3780 of the 4032 pixels of width), which is 378 ppi on 8 by 10 inches, so it clears 300 ppi with some room to crop tighter. This converter has no cropping tool, so do it in a photo editor or let the print service crop it; a lab's automatic crop may cut off edges you wanted.

ppi, dpi and the number stored in the file

Pixels per inch describes how an image is spread over paper. Dots per inch describes how finely a printer places ink. They are different measurements, and printers use many dots to render one pixel. The density value some files carry in their header is only a label that tells software the intended print size. Changing it from 72 to 300 does not add a single pixel; it merely changes the size at which a program proposes to print the same pixels.

That is why pixel dimensions are the number to check. A 1920 by 1080 screenshot, for instance, covers 6.4 by 3.6 inches at 300 ppi (1920 / 300 and 1080 / 300), a little larger than a postcard, and scaled so that its long side spans 10 inches it falls to 192 ppi (1920 / 10), with visible softness in text, and it fills only 5.6 inches of the 8 inch side.

How low can the resolution go

300 ppi is a target, not a cliff. Larger prints are viewed from farther away, and many print shops accept lower densities for posters; the shop's own upload page states its minimum, so read it rather than relying on a rule of thumb. For scale, a 24 by 36 inch poster needs 7200 by 10800 pixels (77.8 megapixels) at 300 ppi but only 3600 by 5400 (19.4 megapixels) at 150 ppi. A 4032 by 3024 phone photo spread over the 36 inch side gives only 112 ppi, so large prints from phone files depend on a low density and a longer viewing distance.

What does not work is stretching a small file. A 1200 by 1800 pixel image printed on A3 paper has about 109 ppi over the 16.5 inch long side, and enlarging it in software only interpolates new pixels without adding detail. Software upscaling cannot recreate detail that was never captured.

JPEG, PNG, TIFF and PDF for print

• JPEG: accepted by most consumer photo services and home printing. Saved with a high quality setting, the loss rarely shows on paper.
• PNG: lossless, so the file is larger than a JPEG for a photo, but it keeps flat graphics and text crisp. Useful for a logo or a designed card.
• TIFF: a professional exchange format that can be lossless and can store CMYK and other color information. Print shops sometimes ask for it.
• PDF: carries fonts, vector shapes and several pages in one file, which is why it is the usual choice for brochures and posters.

This site's converter writes JPEG, PNG, WebP, BMP and ICO. TIFF, PDF and CMYK are not among its outputs, so if a shop requires one of those, that step needs different software. For photo labs that accept JPEG, the conversion works well; for the choice between lossless and lossy for graphics, the lossy and lossless guide goes into detail.

Screen color versus printed color

Screens build color from red, green and blue light, while most printing presses and printers work with cyan, magenta, yellow and black ink. Some saturated screen colors, especially bright blues and greens, fall outside what ink can reproduce, so a print can look duller than the screen however good the file is. This is physics, not a flaw in the file format.

Consumer photo services generally expect sRGB files and convert for their printers. Professional press work may require CMYK, often with a specified profile, and the conversion is best done in software that lets you proof the result. This tool outputs sRGB with no embedded profile, which suits the first case; the color profile article explains what is and is not carried over.

Using the converter for print files

If you convert photos for printing, leave the maximum size on Original size and set quality high, since the converter's size options exist to make images smaller, and a print rarely benefits from that. There is one boundary to know: images above about 16.8 megapixels are scaled down by the tool because some browsers limit canvas size. An A3 print at 300 ppi needs 17.4 megapixels; the tool would trim that to about 3444 by 4870 pixels, roughly 294 ppi. A 16 by 20 inch print needs 28.8 megapixels and would drop to about 229 ppi. For those sizes, convert in another program. The article on how browser-based conversion works explains the limit.

Choosing a file for a lab, a shop or a home printer

The destination decides. A drugstore or online photo lab generally takes a JPEG at the full pixel size of the original and handles color conversion itself, and you should read its upload page for the stated file types and any minimum pixel size. A local print shop doing flyers or posters may ask for a PDF with fonts included, or a TIFF. A home inkjet is driven by software that accepts JPEG and PNG directly and applies its own color management.

When a requirement is unclear, ask the shop two questions: which file types do you accept, and what is the minimum resolution for this size? The answers take a minute and prevent most reprints.