Pixels Per Inch Calculator: PPI Formula and Tables

Pixels per inch (PPI) tells you how tightly pixels are packed into a display or a printed image. A higher PPI means finer detail, sharper text, and smoother curves. A lower PPI means individual pixels become visible — the image looks soft or blocky.

Knowing the PPI of a screen helps you decide if a monitor is worth buying. Knowing the PPI of a print tells you whether the output will look sharp or pixelated at viewing distance. The math is straightforward, and this page gives you everything you need: the formula, worked examples, a reference table for current devices and common print sizes, and the context to interpret the numbers.

What Is PPI (Pixels Per Inch)?

PPI measures the number of pixels that fit into one linear inch. It applies to two things:

• Screens. A display's PPI is fixed by hardware — the panel's pixel count divided by its physical size. You cannot change it. A 27-inch 4K monitor has a specific PPI baked into the glass.
• Digital image files. An image's PPI is metadata that tells software and printers how to map pixels to physical inches. You can change it — either by editing the metadata tag (no pixel change) or by resampling (adding or removing pixels).

PPI is not the same as DPI. DPI (dots per inch) measures how many ink dots a printer places per inch of paper. PPI measures pixels on screens and in files. People use them interchangeably, but they describe different stages of the imaging pipeline. More on that distinction below.

For a broader look at how PPI relates to megapixels, file dimensions, and output quality, see What Is Image Resolution?.

PPI Formula and How to Calculate It

The Diagonal PPI Formula

Screen PPI is calculated using the diagonal pixel count and the diagonal screen size in inches:

PPI = diagonal pixels / diagonal inches

where:

diagonal pixels = sqrt(width_px^2 + height_px^2)

So the full formula is:

PPI = sqrt(width_px^2 + height_px^2) / diagonal_inches

Worked Example 1: 27-inch 4K Monitor

A typical 27-inch 4K monitor has a resolution of 3840 x 2160.

1. Calculate diagonal pixels: sqrt(3840^2 + 2160^2) = sqrt(14,745,600 + 4,665,600) = sqrt(19,411,200) = 4406.8 pixels
2. Divide by diagonal screen size: 4406.8 / 27 = 163.2 PPI

At 163 PPI and a typical desk viewing distance of 24-30 inches, text looks crisp and individual pixels are difficult to spot without leaning in.

Worked Example 2: iPhone 16 Pro

The iPhone 16 Pro has a 6.3-inch display at 2622 x 1206 resolution.

1. Diagonal pixels: sqrt(2622^2 + 1206^2) = sqrt(6,874,884 + 1,454,436) = sqrt(8,329,320) = 2886.1 pixels
2. PPI: 2886.1 / 6.3 = 458.1 PPI

At 458 PPI held 10-14 inches from your eyes, individual pixels are completely invisible. Apple calls this "Super Retina" — marketing term aside, the density genuinely exceeds what the human eye can resolve at phone-distance.

Worked Example 3: Print PPI

Print PPI works differently. Instead of a fixed hardware density, you choose the PPI based on the quality you want:

Required pixels = print size (inches) x desired PPI

To print a sharp 8 x 10-inch photo at 300 PPI, you need: 8 x 300 = 2400 pixels wide, 10 x 300 = 3000 pixels tall. So your source image needs at least 2400 x 3000 pixels (7.2 megapixels).

To convert between pixels and inches at a given PPI, use our pixels to inches and inches to pixels references.

PPI Reference Table by Device and Print Size

Display PPI

Print PPI

300 PPI is the standard for prints viewed up close (photo albums, framed desk prints, business cards). 150 PPI is acceptable for prints viewed at arm's length or farther (wall art, posters). Large-format posters and banners viewed from several feet away can drop to 72-100 PPI and still look fine. For detailed print dimension references, see standard photo dimensions.

PPI vs DPI — Key Differences

The critical point: when a print shop asks for a "300 DPI file," they mean 300 PPI. They want 300 pixels per inch in your image so their printer has enough data. The printer itself runs at a much higher DPI (often 1200-2400) to reproduce those pixels with smooth color gradients.

For the full breakdown, read DPI vs PPI: What's the Difference?. To check or change the PPI metadata embedded in your images, use Pixotter's DPI checker or see How to Check Image DPI.

How PPI Affects Image Quality

PPI alone does not determine quality — viewing distance is the other half of the equation. A 92 PPI monitor looks sharp from across the room and soft when you press your nose to it. The same principle applies to prints.

The Retina Threshold

Apple popularized the term "Retina" for displays where individual pixels become invisible at typical viewing distance. The threshold depends on how far your eyes are from the screen:

This is why a 55-inch 4K TV at 80 PPI looks perfectly sharp from the couch, while a 24-inch 1080p monitor at 92 PPI shows visible pixels at desk distance. The TV has lower PPI but is viewed from much farther away.

Print Quality Thresholds

For printed output, PPI determines how sharp the result looks at the expected viewing distance:

If your image does not have enough pixels to hit 300 PPI at the desired print size, you have three options: print smaller, accept a lower PPI (and the softness that comes with it), or upscale the image with an AI upscaler (results vary — synthetic detail is better than blocky pixels, but not as good as real captured data).

For conversions between centimeters and pixels at a given PPI, see cm to pixels.

FAQ

How do I calculate PPI for my monitor? Use the formula: PPI = sqrt(width_px^2 + height_px^2) / diagonal_inches. For a 27-inch 2560 x 1440 display: sqrt(2560^2 + 1440^2) / 27 = 2938.7 / 27 = 108.8 PPI. You can also search your monitor's model number — manufacturers publish the spec.

What is a good PPI for a monitor? It depends on how close you sit. At typical desk distance (24-30 inches), 110+ PPI looks clean and 150+ PPI looks crisp. Below 100 PPI, text rendering starts to look rough, especially on small font sizes. If sharp text matters to you — and for anyone staring at a screen all day, it should — aim for at least 109 PPI (QHD at 27 inches) or higher.

Does PPI matter for web images? Not directly. Browsers render images based on pixel dimensions, not PPI metadata. A 1200 x 800 image at 72 PPI and the same image at 300 PPI display identically on screen. PPI metadata only matters when the image is printed or when software uses it to determine physical output size.

What PPI do I need for printing photos? 300 PPI is the industry standard for photo-quality prints. At 300 PPI, individual pixels are invisible at normal viewing distance (8-12 inches). For larger prints viewed from farther away — posters, canvas prints — you can drop to 150-200 PPI without noticeable quality loss.

Is higher PPI always better? On screens, yes — up to a point. Beyond the retina threshold for your viewing distance, extra PPI provides no perceptible benefit. For image files, PPI is just a metadata tag that does not affect the actual pixel data. A 3000 x 2000 image contains the same information whether its PPI tag says 72 or 300.

What is the PPI of a 4K TV? It depends on the screen size. A 55-inch 4K TV (3840 x 2160) has about 80 PPI. A 43-inch 4K TV has about 103 PPI. A 65-inch 4K TV drops to about 68 PPI. All of these look sharp from a couch because viewing distance compensates for the lower density.

How is PPI different from resolution? Resolution is the total pixel count (e.g., 3840 x 2160). PPI is the density — how those pixels are distributed across a physical area. Two monitors with the same 3840 x 2160 resolution have different PPI values if their screen sizes differ. Resolution tells you how many pixels exist; PPI tells you how tightly they are packed.

Can I change the PPI of an image? Yes, in two ways. You can change the PPI metadata tag without altering any pixels — this just changes how software interprets the physical size. Or you can resample the image, which adds or removes pixels to hit a target PPI at a specific physical size. The first method is lossless; the second changes the actual image data.