PPI Calculator – Pixels Per Inch, Dot Pitch, and Screen Dimensions

PPI Calculator

Diagonal (inches)

Width (pixels)

Height (pixels)

The PPI Calculator (Pixels Per Inch) computes the pixel density of any screen – smartphone, monitor, TV, or projector – given its diagonal size and resolution (or physical dimensions and resolution). It also returns the dot pitch (distance between pixels), total megapixels, and the actual screen width and height in inches. Understanding PPI is essential for comparing display sharpness, choosing a monitor, or designing digital content for specific pixel densities.

How to Calculate PPI

Formula: PPI = √(horizontal_pixels² + vertical_pixels²) / diagonal_inches

For example, a 24″ monitor with 1920×1080 resolution:

√(1920² + 1080²) = √(3,686,400 + 1,166,400) = √4,852,800 ≈ 2203 pixels

PPI = 2203 / 24 ≈ 91.8 PPI

Why PPI Matters

Image sharpness: Higher PPI means finer detail; at 300+ PPI, pixels become invisible at normal viewing distance (“Retina”).
Print vs. screen: Print typically uses 300 DPI (dots per inch); screens are measured in PPI.
Responsive design: Web developers use device pixel ratios (DPR) based on PPI.
Photo editing: Knowing PPI helps scale images for different displays.

Pixel Density and Viewing Distance

The optimal PPI depends on viewing distance. At arm’s length (phone), you need greater than 300 PPI for a Retina display. For a TV watched from 8 feet, even 80 PPI may be acceptable because the distance masks individual pixels. Our calculator gives you the raw PPI; you can decide if it meets your needs.

Dot Pitch – The Inverse of Pixel Density

Dot pitch (or pixel pitch) is the distance from the centre of one pixel to the centre of the next, usually in millimetres. It is the reciprocal of PPI, converted to mm: dot pitch (mm) = 25.4 / PPI. Smaller dot pitch (e.g., 0.23 mm) means pixels are closer together, giving a smoother, sharper image. This value is often specified for monitors and projectors.

Common Device PPI Examples

Device	Diagonal	Resolution	PPI
iPhone 15 Pro	6.1″	2556×1179	~460
27″ 4K monitor	27″	3840×2160	~163
24″ 1080p	24″	1920×1080	~92
15″ laptop (1080p)	15.6″	1920×1080	~141
65″ 4K TV	65″	3840×2160	~68

Common Mistakes When Calculating PPI

Using wrong diagonal: Some monitors are advertised as e.g., 24″ class (actually 23.8″). Use the exact diagonal if possible.
Mixing units: All lengths must be in inches. Our calculator handles any input but expects inches.
Assuming square pixels: Most modern screens have square pixels; the formula works fine. For non‑square, you’d need horizontal and vertical PPI separately.

Use this PPI calculator to evaluate displays before purchasing, design graphics for specific pixel densities, or satisfy your curiosity about your phone’s sharpness. The step‑by‑step output shows each mathematical operation clearly.

Step‑by‑Step Manual Example

iPhone 15: 6.1″ diagonal, 2556×1179 pixels

Step 1: Compute diagonal pixels = √(2556² + 1179²) = √(6,533,136 + 1,390,041) = √7,923,177 ≈ 2815 pixels

Step 2: PPI = 2815 / 6.1 ≈ 461.5 → ~462 PPI

Step 3: Dot pitch = 25.4 / 462 ≈ 0.055 mm

Step 4: Physical width = (6.1 × 2556) / 2815 ≈ 5.54″; height = 6.1 × 1179 / 2815 ≈ 2.56″

Frequently Asked Questions about PPI

What does PPI mean?

PPI stands for Pixels Per Inch. It measures the pixel density of a screen – the number of pixels in one linear inch. Higher PPI means sharper text and images.

How is PPI calculated?

PPI = √(horizontal_pixels² + vertical_pixels²) / screen_diagonal_inches. For a 1920×1080 24″ monitor, PPI = √(1920²+1080²)/24 ≈ 92.

What is dot pitch?

Dot pitch is the distance between adjacent pixels, measured in millimetres. Smaller dot pitch (e.g., 0.23 mm) gives sharper images. Dot pitch = 25.4 / PPI.

What is a good PPI for a monitor?

For desktop monitors, 90–110 PPI is common. For Retina displays, above 200 PPI (e.g., 220–300) makes pixels indistinguishable at normal viewing distance.