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Ecommerce Glossary

What Is DPI? Dots Per Inch, PPI and Image Resolution Explained

Updated: 14 October 2026

DPI (dots per inch) is the number of printed dots per inch (2.54 cm), while image resolution is the number of pixels in a photo, for example 2000 × 2000 px. How large and sharp a print can be depends on the pixels: the DPI stored in a file only changes the print size. Below we also explain how DPI differs from PPI, how many pixels a print needs and what image quality depends on.

What is DPI? Dots per inch explained

DPI (dots per inch) is the number of dots a printer places along one inch (2.54 cm) of paper. It describes the output device: the more dots per inch, the finer the detail a printer can reproduce.

Inkjet printers typically work at 300-720 DPI and laser printers at 600-2,400 DPI (Wikipedia: Dots per inch). Those figures describe the hardware, not your photo. Inside a JPG file, DPI is just a field in the header: the JFIF format stores pixel density either per inch or per centimetre (Wikipedia: JFIF).

Changing the DPI does not improve quality

Change the DPI without adding pixels and only the print size changes. The same file tagged 72 DPI and 300 DPI holds exactly the same detail; at the higher value your editor simply reports a smaller size in inches or centimetres. Photoshop only creates new pixels when you tell it to resample, and then it has to interpolate them (Spoon Graphics).

From the studio: our standard file is a JPG of 2000 × 2000 px at 72 DPI in RGB. At 72 DPI an editor reports a print size of about 27.8 in (70.6 cm); type in 300 DPI without resampling and it shows about 6.7 in (16.9 cm), although not a single pixel has changed. When photos are going into a printed catalogue, our product photography pricing includes a 6K Resolution add-on: 6000 px at 300 DPI.

How to check and change the DPI of an image

Windows: right-click the file, choose Properties and open the Details tab. Horizontal resolution and Vertical resolution show the stored DPI, Dimensions shows the pixel count.
Mac (Preview): Tools > Adjust Size shows the Resolution field. To change the print size without losing detail, deselect Resample image first (Apple Support).
Photoshop: Image > Image Size. With Resample switched off, a new Resolution value only recalculates the print size; with Resample on, Photoshop adds or removes pixels.
No software: change the pixel dimensions with our free resize image online tool.

DPI on a computer mouse means something else

If you arrived here from a gaming mouse spec sheet: there, DPI describes how sensitive the sensor is. DPI is a misnomer in the gaming world, and many manufacturers use it to mean CPI, counts per inch (Wikipedia: Computer mouse). It has nothing to do with the resolution of a photo or a print.

DPI vs PPI: what is the difference?

PPI (pixels per inch) is pixel density: in an image file it says how many pixels will be laid along each inch of a print, and on a screen how many pixels fit into one inch of the display. DPI is the output resolution of a printer, PPI the input resolution of an image (Wikipedia: Dots per inch).

	DPI	PPI
Stands for	dots per inch	pixels per inch
Describes	ink or toner dots a printer lays on paper	pixels of an image file or a screen
Where you meet it	printer specifications	Image Size dialogue, display specifications
Typical values	inkjet 300-720, laser 600-2,400	300 for print viewed up close, about 82-163 on 27-inch monitors

The two numbers are not the same. A printer builds the colour of each pixel out of several tiny ink dots, so for inkjet printing the image PPI is usually set at half the printer's DPI or less: a 600 DPI printer can be fed a 300 PPI image (Wikipedia: Pixel density).

In everyday use, though, the two terms are used interchangeably (Spoon Graphics), and when someone asks for "a 300 DPI file" they mean 300 pixels per inch at the final print size. That is how we use the word in the rest of this page.

Screen pixel density and Retina displays

Screen PPI is worked out from the diagonal: take the square root of width² + height² in pixels and divide it by the diagonal in inches (Wikipedia: Pixel density). A 27-inch Full HD monitor therefore has about 82 PPI, and a 27-inch 4K monitor about 163 PPI.

On dense screens the browser draws each CSS pixel with several physical pixels. The devicePixelRatio value is 1 on a classic 96 DPI display and 2 on HiDPI/Retina screens, and modern phones often report more than 2 (MDN). A product gallery shown 800 CSS pixels wide therefore needs a file 1600 px wide to stay sharp on such a screen.

Laptop, notebook and mug on a wooden desk by a window

Image resolution: pixels and megapixels

Image resolution is the number of pixels that make up a digital image, given as width × height (for example 2000 × 2000 px) or as a total in megapixels. It sets how much product detail a file can hold and how large it can be shown or printed before it turns soft.

One megapixel is a million pixels. A 2000 × 2000 px file is 4 MP, a Full HD screen (1920 × 1080) shows about 2.1 MP, and 4K UHD (3840 × 2160) has exactly four times as many pixels as Full HD (Wikipedia: 4K resolution). We look at that standard in more depth in what is 4K resolution.

Pixel dimensions	Megapixels	Example
1920 × 1080 px	about 2.1 MP	Full HD screen
2000 × 2000 px	4 MP	standard JPG from a marszalstudio shoot
3840 × 2160 px	about 8.3 MP	4K UHD screen
6000 × 4000 px	24 MP	3:2 photo from a 24 MP camera

A file has no size in inches or centimetres of its own. It only gets a physical size once you set a print density, its DPI, and changing that density does not change the pixel count (Wikipedia: Dots per inch). So with product photos the first question is always "how many pixels?", and only then "what DPI?".

Do more megapixels mean a better photo?

Not necessarily. Megapixels tell you how much detail a sensor can record, not how much it actually did: camera shake, noise or poor exposure ruin a file whatever its pixel count. More on that below, under what image quality depends on.

The other trap is upscaling a small file. Software that adds pixels has to interpolate them from their neighbours, and AI upscalers invent detail that was never in the original (Wikipedia: Image scaling). With product photos that is a real risk: the weave of a fabric, the small print on a label or the cut of a gemstone can come out different from the real thing.

Camera with a neck strap lying on desert sand

How many pixels do you need for print?

The number of pixels you need for a print is the print size in inches multiplied by the target DPI; if you work in centimetres or millimetres, convert to inches first. Run it backwards and the pixel count divided by the DPI gives the largest print size at that quality.

pixels = size in inches × DPI
pixels = size in cm ÷ 2.54 × DPI
print size in inches = pixels ÷ DPI

Format	Size	Pixels at 300 DPI	Pixels at 150 DPI
photo print	6 × 4 in (152 × 102 mm)	1800 × 1200 px	900 × 600 px
A5	148 × 210 mm	1748 × 2480 px	874 × 1240 px
A4	210 × 297 mm	2480 × 3508 px	1240 × 1754 px
A3	297 × 420 mm	3508 × 4961 px	1754 × 2480 px
A2	420 × 594 mm	4961 × 7016 px	2480 × 3508 px

A-series sizes follow ISO 216 (Wikipedia: ISO 216), and the results are rounded to the nearest pixel. Note that an A2 poster at 150 DPI needs exactly the same pixels as an A4 sheet at 300 DPI.

For print that people hold in their hands, such as flyers, catalogues and packaging inserts, printers ask for 300 DPI at the final size. Herefordshire printer Orphans Press, for example, wants images at 300 dpi, artwork in CMYK, 3 mm of bleed and ideally a PDF/X-3 file (Orphans Press). For large posters and banners, which are viewed from further away, 150 DPI is common practice and a sensible balance between detail and file size (Tradeprint).

From the studio: a 2000 × 2000 px file is enough for a print of about 6.7 × 6.7 in (16.9 cm) at 300 DPI, or about 13.3 × 13.3 in (33.9 cm) at 150 DPI. The 6000 px side from the 6K Resolution add-on gives 20 in (50.8 cm) at 300 DPI, more than the long side of an A3 sheet. If your printer has sent exact dimensions, the Individual size add-on prepares the file at the size or resolution stated in your brief.

Common mistakes when preparing photos for print

Changing 72 to 300 DPI in the metadata and assuming the file is now print-ready. What counts is whether there are enough pixels for the format.
Stretching a photo taken from a website to poster size. Software will fill in the missing pixels, but it cannot recover detail that was never captured.
Sending an RGB file to a printer that works in CMYK. Check the printer's specification before you export.
Saving a JPG over and over again: some quality is lost every time the image is recompressed (Wikipedia: JPEG).

Image resolution for online shops and marketplaces

Image resolution for the web is simply the pixel dimensions of the file: how large and how sharp a photo looks in your shop depends on its pixels, the width your theme gives it and the pixel density of the screen. The familiar "72 DPI for web" rule goes back to the Mac, which since the 1980s has used 72 PPI as its default display density, while Windows used 96 PPI (Wikipedia). It is not a platform requirement.

Marketplaces and shop platforms state their image requirements in pixels, megapixels and megabytes, never in DPI:

Platform	Requirements	Recommendation
Amazon UK	main image on pure white (RGB 255, 255, 255), product taking up about 85% of the frame, 500 to 10,000 px on the longest side; JPEG preferred, TIFF, PNG and non-animated GIF accepted	at least 1,000 px on the longest side to enable zoom, larger for the best zoom
eBay UK	minimum 500 × 500 px, up to 24 photos per listing, 12 MB per photo, no logos or watermarks	about 1600 × 1600 px
Google Merchant Center	from 31 January 2027 at least 500 × 500 px for all products; maximum 64 MP and 16 MB; no watermarks or promotional overlays	around 1500 × 1500 px or above
Shopify	up to 5000 × 5000 px or 25 MP, file smaller than 20 MB	2048 × 2048 px for square images

Our standard 2000 × 2000 px file fits all four: it clears Amazon's zoom threshold, beats the sizes eBay and Google recommend and stays well inside Shopify's limit. Selling handmade or vintage goods? Our guide to selling on Etsy UK covers listing photos for that platform.

Pixel size is not everything: file weight and format

Large pixel dimensions do not have to mean a heavy page. File weight comes down to photo compression and format: WebP or a well-tuned JPG for the gallery, PNG wherever you need a transparent background. That is why packshots ordered with the Remove background add-on are delivered as PNG files with a transparent background.

Image quality: what it depends on

Image quality is how faithfully and clearly a photo shows its subject: it is sharp, well exposed, true to colour, low in noise and has enough resolution. For a product photo it comes down to one question: will the customer see on screen what arrives in the box?

Resolution is only one factor. A blurred or noisy 24 MP file shows less real detail than a sharp 4 MP one, because its pixels carry less information about the product.

Sensor and lens

A larger sensor gathers more light, and at equal exposure its signal-to-noise ratio rises with the square root of its area. Full frame measures about 36 × 24 mm, APS-C around 23.6 × 15.6 mm (Wikipedia: Image sensor format). That is why a full-frame camera at the same settings usually shows less noise than the small camera sensor in a phone.

The lens is responsible for the sharpness of fine detail and edges. A high-megapixel sensor can only record as much detail as the lens projects onto it.

Camera lens standing on a white stone plinth

Light, exposure and noise

An underexposed shot has to be brightened in editing, and that drags noise out of the shadows. Raising the ISO does the same. In the studio the answer is the amount and control of light: the product gets enough of it to shoot at low ISO with a depth of field that covers the whole object.

Colour and file format

Colour depends on white balance and the colour profile. For an online shop, sRGB is the safe choice: it is the standard colour space for the web and the one assumed for images without an embedded profile (Wikipedia: sRGB). The final save can still spoil things: JPEG is lossy compression, typically around 10:1, and every re-save loses a little more (Wikipedia: JPEG).

A RAW file stores the sensor data before that compression and leaves headroom for correcting exposure and colour, but what ends up in the shop is a JPG, WebP or PNG.

Mistakes that lower the quality of product photos

Blur: camera shake, or focus on an edge instead of the label (we explain the fixes in how to get sharp photos).
Wrong exposure: a blown-out background merges with the edge of a light product, while underexposure adds noise.
Wrong white balance: the product shows a different shade from the one the customer will unpack.
Over-editing: heavy sharpening and saturation that change the look of texture and colour.
The wrong file: a JPG saved over and over, or a small file blown up to a large format.

From the studio: basic editing of crop, exposure and colour is included in the price of every photo. We prepare products before the shoot by ironing clothes, polishing surfaces and arranging each item, because no resolution can make up for dust and creases. In the live session, which is always included, you mark each photo as OK or for correction as the shoot goes on, so you judge quality during the session rather than after the files arrive.

Frequently asked questions

What does 300 DPI mean?

300 DPI means 300 dots, and in an image file 300 pixels, for every inch (2.54 cm) of the print. It is the usual requirement for print viewed up close, such as flyers and catalogues. A print 4 inches wide needs 1200 pixels at 300 DPI.

Does DPI matter for product photos shown online?

Not for quality. The DPI value only tells software how large a print would be. Online, what counts is the pixel count: a 2000 × 2000 px file holds the same detail whether it is tagged 72 or 300 DPI, and Amazon, eBay, Google and Shopify set their limits in pixels.

How many pixels is A4 at 300 DPI?

An A4 sheet (210 × 297 mm) needs 2480 × 3508 pixels at 300 DPI, which is about 8.7 megapixels. At 150 DPI half that in each direction is enough: 1240 × 1754 px. The formula is size in cm ÷ 2.54 × DPI.

How do I check the DPI of an image?

On Windows, right-click the file, choose Properties and open the Details tab to see the horizontal and vertical resolution and the pixel dimensions. On a Mac, open the image in Preview and choose Tools > Adjust Size. In Photoshop, use Image > Image Size.

How do I change DPI without losing quality?

In Photoshop's Image Size dialogue or Preview's Adjust Size window, switch off resampling and enter the new resolution. The pixel count stays the same and only the print size changes, so quality does not suffer. Adding pixels cannot restore detail the file never had.

What is the difference between DPI and PPI?

DPI counts the ink dots a printer puts on each inch of paper. PPI counts the pixels of an image or a screen per inch. In image editors "DPI" usually means the PPI of the file, that is how densely its pixels will be spread across the print.

What resolution should product photos be for an online shop?

Platforms set requirements in pixels, not DPI. Amazon UK enables zoom from 1,000 px on the longest side, eBay recommends about 1600 × 1600 px, Google Merchant Center around 1500 × 1500 px and Shopify 2048 × 2048 px for square images. A 2000 × 2000 px file suits all of them.

What does image quality depend on?

On sharpness, exposure, colour accuracy, noise, resolution and the way the file is saved. The sensor and lens set the limits, but light, technique and editing decide the result. A high megapixel count alone does not guarantee a good photo.