Is your photo sharp enough to print? The 30-second test

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Published 19 September 2026 · about 7 min read

The short answerTo know whether a photo is sharp enough to print, divide its number of pixels by the print size in inches (or by the size in centimetres, then multiply by 2.54): you get the resolution in dots per inch, dpi. Print shops aim for 300 dpi, about 118 pixels per centimetre. An A4 sheet (21 × 29.7 cm (8.3 × 11.7 in), 8.3 × 11.7 in) therefore needs about 2480 × 3508 pixels; a 4 × 6 in print about 1200 × 1800; an 8 × 10 in print about 2400 × 3000. On fabric, viewed at arm's length, 150 dpi still looks right — half the pixels on each side. Enlarging a file in software adds no detail: find the original photo, before it went through a messaging app, a screenshot or a social-media download.

Test your photoThe tool warns you if the resolution is too low for the size you pick. Nothing is uploaded before you order.

You have a photo you love and one simple question: will it look right once printed, or will it turn into a mush of pixels? There is a definite answer, it takes thirty seconds, and it needs no software.

The principle: a photo has no "size" in centimetres or inches. It has a number of pixels. The centimetres only appear when you decide to spread it over paper or fabric. The more you spread it, the bigger each pixel gets, and at some point you see them. Everything else in this article is that calculation, plus the traps that make you think you have a good photo when all you have is a shrunken copy.

The 30-second test: pixels ÷ inches

The full formula:

dpi = pixels ÷ inches (or pixels ÷ (centimetres ÷ 2.54))

Dpi — dots per inch — is the term used throughout printing. Strictly, an image has ppi and a printer has dpi; in practice everyone says dpi, and what you are measuring is the density of pixels once printed.

The version to remember: divide the pixel width by 300 to get the maximum print width in inches at 300 dpi. In centimetres, divide by 118 — or by 120, which is quicker and still right.

Example: a photo 3024 pixels wide. 3024 ÷ 300 = about 10. It holds up at 10 inches (25 cm) wide at 300 dpi. Beyond that, the density drops.

Do the test on both dimensions, width and height, and look at the one that limits you. A vertical photo of 3024 × 4032 px holds up at 10 × 13 in (25 × 33 cm (9.8 × 13 in)): it prints at A4 or 8 × 10 in with no trouble.

What 300 dpi is, and whether you really need it

300 dpi has been the print industry's reference for decades. At that density, the eye no longer picks out individual dots at reading distance — 30 to 40 cm, about a foot. It is the logical target for a print you look at closely.

But 300 dpi is not a law. It is a viewing distance disguised as a number. The further away you look, the less you need. And not every object is looked at the same way:

A framed print on the wall is seen up close and then from across the room. 300 dpi is comfortable; 200 dpi already looks very good.
A t-shirt or a tote bag is rarely looked at from 20 cm. The fabric also has its own texture, a weave that absorbs fine detail. Around 150 dpi, the result still looks right.
A mug is in your hand, 20 cm from your eyes: aim for 300 dpi as you would for a framed print.

Here is what that means in pixels, by the print width you are aiming for:

Print width	Pixels for 300 dpi	Pixels for 150 dpi
4 in · 10 cm	1200 px	600 px
6 in · 15 cm	1800 px	900 px
8 in · 20 cm	2400 px	1200 px
10 in · 25 cm	3000 px	1500 px
12 in · 30 cm	3600 px	1800 px

Going from 300 to 150 dpi halves the pixels on each side, so it divides the total number of pixels by four. That is why a file that looks small can still be enough for fabric.

How many pixels for an A4, an 8 × 10, a 4 × 6?

An A4 sheet measures 21 × 29.7 cm (8.3 × 11.7 in), or 8.3 × 11.7 in. At 300 dpi it needs 2480 × 3508 pixels; at 150 dpi, 1240 × 1754. An 8 × 10 in print needs 2400 × 3000 pixels at 300 dpi. A 4 × 6 in print, 1200 × 1800.

Good news: most phones from the last ten years clear those thresholds. A 12-megapixel sensor produces 3024 × 4032 px. A 48-Mpx sensor can go higher, but it often saves 12-Mpx files by default — again, what settles it is the pixel count of the file, not the spec sheet. If your photo comes straight from the phone that took it, with no detour, it prints at A4. Check the dimensions anyway; it takes ten seconds.

So the problem is almost never the camera. It is what happened to the photo afterwards.

How to see the pixel count of your photo

The number is written in plain sight; you just need to know where to look:

iPhone: open the photo in Photos, swipe up or tap the (i) button. The dimensions appear under the date, as "3024 × 4032".
Android: in Google Photos or the gallery, open the photo, then the ⋮ menu or "Details". Same idea.
Windows: right-click the file, Properties, Details tab, "Dimensions" line.
Mac: select the file and press Cmd + I, or open it in Preview then Tools › Adjust Size.

Note the file size while you are there. A photo of several megabytes is probably an original. A photo of only a few dozen kilobytes has very probably been compressed along the way, even if its dimensions look fine.

Why your WhatsApp photo prints blurry

This is trap number one, and it is invisible on screen. A photo may have passed through several machines that shrank it without telling you. The usual culprits:

WhatsApp, Messenger, iMessage, messaging apps in general. They recompress images to save bandwidth. The photo still looks fine on a phone screen, where it is 7 cm wide. Spread over 30 cm, it falls apart. Workaround: ask the sender to resend the photo as a document (paperclip › Document), which switches compression off.
The screenshot. A screenshot cannot contain more pixels than the screen displays, and the picture inside it only takes up part of that. Screenshotting a photo to get hold of it is photographing a photocopy.
Photos downloaded from social media. What is published online is already a lightened version. It is not the original, whatever happens.
The phone's digital zoom. Beyond the optical zoom, the phone crops into the sensor and enlarges the result. You get an image with the usual dimensions but less real detail in it. On phones with several lenses, only the zoom levels that match a real lens stay optical; the others are crops. When in doubt, check the pixel count of the resulting file.
E-mail attachments. Some mail clients offer "Small / Medium / Actual size" when sending. You want Actual size.

To recover the original: go back to the source, the gallery of the phone that took the picture. Transfer it by AirDrop, by cable, by a file-sharing service or a download link. If your photos live in iCloud in optimised mode, turn on "Download and Keep Originals" before copying.

Can a photo be enlarged without losing quality?

No. And it matters to understand why, because many tools suggest otherwise.

When you take an image from 800 to 3000 pixels wide in software, it does not go and fetch the missing information: it exists nowhere. It manufactures it, computing intermediate pixels from their neighbours. The file gets bigger; the picture does not get better. The typical result is a soft image with smeared edges.

AI upscalers do a little better: they invent plausible detail rather than blur. Sometimes convincing on a texture, almost always doubtful on a face, because the invented features are no longer quite the person's. On an object you are giving as a gift, that is a gamble.

And none of this repairs blur that was there from the start: camera shake, missed focus, a photo taken in the dark. Too few pixels is a size problem; blur is an information problem. No enlargement recreates an edge that was never recorded.

The practical conclusion: do not try to rescue a small file. Look for the big original. It almost always exists somewhere.

What photo size for a mug or a t-shirt?

Designs on objects are smaller than an A4: a mug's print area wraps around the cup, a t-shirt's or a tote bag's covers a chest or one face. Useful landmark: a chest design is usually around 20 to 25 cm (8 to 10 in) wide, a mug design around 20 cm (8 in). Take the width shown in the preview, look it up in the table above, and you have your answer.

Two points specific to fabric, which often matter more than resolution itself:

Contrast comes first. A dark photo printed on dark fabric reads badly, even at 4000 pixels. A legible, contrasty image with a sharp subject and a simple background holds up better than a technically perfect but cluttered one.
Framing is decided beforehand. Cropping tight means throwing pixels away. If you keep half the width of the image, you halve the pixels available. Check the pixel count after cropping, not before.

On Pose ton design you can check all of this visually with no commitment: the preview is computed in your browser, on your own device. Your photo is sent nowhere until you order. You drop the image in, see it at once on the whole range with prices, judge the framing, and close the tab if you do not like it. Prices, delivery countries and lead times are on the page of facts.

The method given here is nothing specific to this site: it is the same division at any printer. Keep it; it comes in handy every time someone asks "can you send me the photo in good quality?".

Frequently asked questions

How many megapixels do I need to print a photo?

For an A4 print at 300 dpi you need about 2480 × 3508 pixels, which is 8.7 megapixels; for an 8 × 10 inch print, about 2400 × 3000 pixels, or 7.2 megapixels. Most recent phones exceed that. Megapixels alone do not settle it: what matters is the number of pixels on the shorter side compared with the print size.

How many pixels do I need for a 4 × 6 print?

1200 × 1800 pixels at 300 dpi. At 150 dpi, which is fine for fabric but not for a print you hold in your hand, 600 × 900 pixels.

Is a JPEG worse than a PNG for printing?

No, not in itself. A JPEG straight out of a camera or phone prints perfectly well. What degrades an image is repeated recompression every time it is shared. An original JPEG beats a PNG made from a screenshot.

Can I print a portrait-mode photo with a blurred background?

Yes. Background blur is a deliberate effect, not a resolution problem. Just check that the subject itself is sharp and that the pixel dimensions match the print size you are aiming for.

How many fewer pixels do I need at 150 dpi instead of 300?

Half as many on each side, so a quarter of the total. An A4 print needs 2480 × 3508 pixels at 300 dpi and 1240 × 1754 pixels at 150 dpi. On fabric, viewed from a normal distance, 150 dpi still looks right.

Do I have to upload the photo to find out whether it will print well?

No. On Pose ton design the preview is computed in your own browser: nothing is transmitted before you order. The print file only goes to the printer when you pay, and it is deleted after dispatch.

What if I ordered with a photo that was too small?

A personalised item is exempt from the 14-day right of withdrawal under EU consumer law (Directive 2011/83/EU, article 16 c). A damaged item, or one that does not match the order, is reprinted free of charge. Hence the point of doing the pixel count before you confirm.

Can I print any photo I like?

No. You must hold the rights to the image you upload: your own photos, or ones you have permission to use. An image found online or a protected work cannot be printed freely.

Upload a photo and see it on everythingFrom $23.00, shipping included. Nothing is sent before you order.