Do I need to change the DPI to 300 before printing?

Changing only the DPI number does not change the pixels, so it does not change print quality. What matters is that the image has enough pixels for the print size at the DPI you want; setting the DPI field then tells the printing software the intended physical size.

What DPI should I use for a poster?

Posters are usually viewed from further away than a photo in your hand, so 150 DPI is a common and practical choice. It needs a quarter of the pixels that 300 DPI does, which also keeps large sizes within what a browser can process.

Can I print a 4x6 photo from a 1 megapixel image?

You can, but at 4 x 6 inches a 1 MP image (for example 1000 x 1000 pixels) gives well under 300 pixels per inch on the long side, so it will look soft up close. A 4x6 at 300 DPI needs 1200 x 1800 pixels, which is about 2.2 megapixels.

Why does my print come out a different size than I set?

The print dialog is probably scaling the image to fit the page. Choose actual size or 100% scale, and check that the paper size in the dialog matches the paper in the printer.

Image Size for Printing: DPI, Pixels and Inches Explained

Printing is where pixel counts stop being abstract. A photo that looks perfect on a phone can print soft and blocky, and a carefully sized file can still come out the wrong size because of one setting in the print dialog. Everything here comes down to one formula and a few practical habits, with worked numbers for the print sizes people actually use.

Quick answer: Pixels needed = print size in inches × DPI. For a sharp photo print, aim for 300 DPI: a 4x6 inch print needs 1200 × 1800 pixels, an A4 page needs 2480 × 3508. For posters viewed from a distance, 150 DPI is usually enough. Crop to the print’s aspect ratio first, then resize, and print at 100% scale.

The one formula you need

Pixels = inches × DPI

For millimetres, convert first: pixels = (mm ÷ 25.4) × DPI, since one inch is exactly 25.4 mm. Round to the nearest whole pixel.

Turned around, the same formula tells you how large an existing image can print: inches = pixels ÷ DPI.

DPI here means “dots per inch”, although for digital images it really describes pixels per inch (PPI). Printer manufacturers use DPI for the physical ink dots their hardware lays down, which is a different number. In everyday use, and in most software including ResizeAny, the two terms are used interchangeably for the image setting.

What 72, 96, 150 and 300 DPI mean

DPI	Where you meet it	What it is good for
72	Old default in many cameras and programs	A historical screen convention; meaningless for print on its own
96	Default for unit conversion on Windows and in many apps	Converting cm or inches to pixels for screen use
150	Posters, banners, large prints	Prints viewed from arm’s length or further
300	Photo prints, documents, cards	Prints held in the hand and viewed closely

None of these is a law. 300 DPI is a widely used target because at normal reading distance most people cannot see individual pixels beyond that. 150 DPI looks fine on a wall poster you see from a metre or two away. Going much higher than 300 for an ordinary photo print rarely shows a visible improvement.

Pixel dimensions for common print sizes

All values use the formula above and are rounded to the nearest pixel. Megapixels (MP) are for the 300 DPI version.

Print size	Physical size	At 150 DPI	At 300 DPI	MP at 300 DPI
4x6 photo	4 × 6 in	600 × 900	1200 × 1800	2.2
5x7 photo	5 × 7 in	750 × 1050	1500 × 2100	3.2
8x10 photo	8 × 10 in	1200 × 1500	2400 × 3000	7.2
A4	210 × 297 mm	1240 × 1754	2480 × 3508	8.7
A5	148 × 210 mm	874 × 1240	1748 × 2480	4.3
Passport photo	35 × 45 mm	207 × 266	413 × 531	0.2
Business card	3.5 × 2 in	525 × 300	1050 × 600	0.6

Worked example: A4

A4 is 210 × 297 mm. Width: 210 ÷ 25.4 = 8.27 in, × 300 = 2480 pixels. Height: 297 ÷ 25.4 = 11.69 in, × 300 = 3508 pixels. At 150 DPI, halve them: 1240 × 1754.

Worked example: passport photo

35 mm ÷ 25.4 × 300 = 413.4, so 413 pixels wide. 45 mm ÷ 25.4 × 300 = 531.5, which rounds to 531 pixels tall (the unrounded value is 531.496). Note that the official rules for passport photos also cover head size, background and lighting, and they vary by country; check the current rules from the issuing authority before printing.

How big can my phone photo print?

A common phone camera produces 12 MP images of 4000 × 3000 pixels. Using inches = pixels ÷ DPI:

At 300 DPI: 4000 ÷ 300 = 13.3 in and 3000 ÷ 300 = 10 in, so about 13.3 × 10 inches (roughly 34 × 25 cm).
At 150 DPI: 4000 ÷ 150 = 26.7 in and 3000 ÷ 150 = 20 in, so about 26.7 × 20 inches.

So a sharp 12 MP photo easily covers 4x6, 5x7, 8x10 and A4 at 300 DPI. In practice, the limiting factor is often not the pixel count but focus, motion blur, noise from low light, or digital zoom, which crops the sensor and leaves far fewer real pixels than the file size suggests.

Crop to the print ratio first

Print sizes have different shapes from camera images, and this is where many prints go wrong: the lab or printer either crops the edges for you or leaves white bars.

Format	Aspect ratio
Most phone photos	4:3
4x6 print	3:2
5x7 print	7:5
8x10 print	5:4
A-series paper (A4, A5)	about 1.414:1

Worked example: 12 MP photo to a 4x6 print

A 4000 × 3000 image is 4:3. A landscape 6 × 4 inch print is 3:2. Keeping the full width of 4000 pixels, a 3:2 crop needs a height of 4000 ÷ 1.5 = 2667 pixels. So you crop from 4000 × 3000 to 4000 × 2667, losing 333 rows, about 11% of the height. Then resize to 1800 × 1200 for 300 DPI.

Do this crop yourself so you decide what is cut: the top of a head, or empty sky.

Worked example: 12 MP photo to A4

Held in portrait, the photo is 3000 × 4000. A4’s ratio is about 1:1.414. Keeping the full 4000-pixel height, the width becomes 4000 ÷ 1.414 = 2828 pixels. Crop to 2828 × 4000, then resize to 2480 × 3508. Both numbers are below the cropped size, so you are shrinking, not enlarging, which is what you want.

Upscaling does not add detail

If your image has fewer pixels than the table asks for, resizing it up to the target will produce a file with the right numbers, but not a sharper print. A good resampling filter such as Lanczos-3 (which ResizeAny uses) creates new pixels by smoothly interpolating between existing ones. That avoids jagged blocks, but it cannot invent eyelashes, text or texture that the original never captured. The print will look soft rather than pixelated.

Practical options when you are short of pixels:

Print smaller. An image that is 1200 × 1500 makes a crisp 4 × 5 in print at 300 DPI, or a softer 8 × 10 at 150 DPI.
Accept a lower DPI for larger, distance-viewed prints.
Find the original file. Images saved from messaging apps and social networks are often downscaled copies.

The DPI metadata myth

Every JPG or PNG can carry a DPI number in its metadata. Changing that number alone does nothing to the image itself. A 1200 × 1800 file tagged 72 DPI and the same file tagged 300 DPI have identical pixels and print identically if you print both at 4 × 6 inches.

What the tag does change is the default size some software suggests. At 300 DPI, a program reads 1200 × 1800 as 4 × 6 inches. At 72 DPI, it reads the same pixels as about 16.7 × 25 inches. That is why people believe “72 DPI images print badly”: the image was not worse, the program simply proposed printing it much larger.

So the honest rule is: pixel dimensions decide the quality, the DPI tag decides the default physical size. Set both correctly and the file behaves predictably everywhere.

Print at 100% scale

Most print dialogs default to “fit to page” or “shrink to printable area”, which scales the image so it fits within the margins. Your carefully sized 4 × 6 inch image then prints at some other size. Before printing:

Choose Actual size, 100% or No scaling in the print dialog.
Make sure the selected paper size matches the paper in the tray.
For borderless prints, expect a small amount of trimming at the edges; keep important content away from them.

Sizing an image for print in ResizeAny

Open the resizer and add your photo (up to 70 MB).
Use Crop to match the print’s aspect ratio, as in the worked examples above. The crop tool has 3:2, 7:5 and 5:4 presets (and their portrait versions) for photo prints; for A-series paper, use freeform.
Set the unit to inch, cm or mm and type the print size, for example 6 × 4 inches.
Set DPI to 300 (or 150 for posters). This matters: with DPI on Auto, unit conversion uses 96 DPI, so 4 × 6 inches would become only 384 × 576 pixels. At 300 DPI it becomes 1200 × 1800.
Export as JPG or PNG. The DPI you chose is written into the file, so printing software reads the intended size.

Ready-made presets such as 4x6 inch, A4 paper and passport photo fill in the dimensions; check the DPI field before exporting. The print, paper and photo presets list many more sizes.

Large posters and the 120 MP limit

Because all processing happens in your browser, ResizeAny limits output to about 120 megapixels; beyond that, devices commonly run out of memory. Most prints are nowhere near this, but large posters at 300 DPI can be:

Poster size	At 300 DPI	At 150 DPI
18 × 24 in	5400 × 7200 (38.9 MP)	2700 × 3600 (9.7 MP)
24 × 36 in	7200 × 10800 (77.8 MP)	3600 × 5400 (19.4 MP)
36 × 48 in	10800 × 14400 (155.5 MP, over the limit)	5400 × 7200 (38.9 MP)
A1 (594 × 841 mm)	7016 × 9933 (69.7 MP)	3508 × 4967 (17.4 MP)
A0 (841 × 1189 mm)	9933 × 14043 (139.5 MP, over the limit)	4967 × 7022 (34.9 MP)

For sizes over the limit, use 150 DPI. It is the sensible choice for posters anyway, and very few source photos have enough real detail to fill a 36 × 48 inch print at 300 DPI: a 12 MP phone photo would have to be enlarged more than tenfold in pixel count.

Try it

Pick your size from the print and paper presets, or open the resizer, enter the size in inches or millimetres and set the DPI yourself. Several photos for the same print size can go through bulk image resize together, up to 10 at a time.

Related guides: JPG vs PNG vs WebP vs AVIF helps you pick the file format to send to a printer, and how to reduce an image to 20KB, 50KB or 100KB covers the opposite case, shrinking a photo for an upload limit.