liminfoDPI/PPI Calculator
Free web tool: DPI/PPI Calculator
PPI
163.2
Dot Pitch
0.156 mm
Physical Size
23.5" x 13.2"
Aspect Ratio
16:9
Total Pixels
8.29 MP
About DPI/PPI Calculator
The DPI/PPI Calculator is a free, browser-based tool for computing the pixel density of any digital display. Enter the screen resolution (width × height in pixels) and the diagonal size in inches, and the calculator instantly returns the pixels per inch (PPI), dot pitch in millimeters, physical screen width and height in inches, simplified aspect ratio, and total megapixel count. A reverse mode lets you estimate the resolution of a screen from a target PPI and diagonal size.
Graphic designers, UI/UX designers, software developers, hardware reviewers, and display buyers use PPI calculations to compare screen sharpness across different sizes and resolutions. A 27-inch 4K monitor (163 PPI) looks sharper than a 27-inch 1440p monitor (109 PPI) even though both are the same physical size. This calculator makes such comparisons straightforward. Ten popular device presets — from iPhone 15 Pro to MacBook Pro 16" and 32-inch 4K monitors — are included for one-click setup.
All calculation happens inside your browser with no server communication. The forward mode uses the Pythagorean theorem to calculate the diagonal pixel count (√(w²+h²)), divides by the physical diagonal to get PPI, and derives dot pitch as 25.4 / PPI. The reverse mode estimates the resolution from a given PPI and diagonal assuming a 16:9 aspect ratio. No sign-up, no download, fully offline after the first page load.
Key Features
- Calculates PPI (pixels per inch) from resolution and diagonal screen size
- Outputs dot pitch in millimeters — useful for display engineering and quality assessment
- Shows physical width and height of the screen in inches
- Computes simplified aspect ratio (e.g., 16:9, 4:3) using the GCD algorithm
- Displays total megapixel count for quick resolution comparison
- Reverse mode: estimate screen resolution from a target PPI and diagonal size (assumes 16:9)
- 10 built-in device presets: iPhone 15 Pro, iPhone 15 Pro Max, Samsung S24 Ultra, iPad Pro, MacBook Pro 14"/16", 4K 27"/32" monitors, 1080p and 1440p 27" monitors
- 100% client-side — no server requests, works offline, no account required
Frequently Asked Questions
What is PPI and how is it different from DPI?
PPI (pixels per inch) describes the pixel density of a digital display — how many pixels fit into one inch of screen space. DPI (dots per inch) is a printing term describing how many ink dots a printer places per inch. For screens, PPI is the correct term. This calculator computes PPI for displays, though the terms are often used interchangeably in consumer contexts.
How is PPI calculated from resolution and screen size?
The formula is: diagonal_pixels = √(width² + height²); PPI = diagonal_pixels / diagonal_inches. For example, a 3840×2160 (4K) screen on a 27-inch monitor: diagonal_pixels = √(3840² + 2160²) = √(14745600 + 4665600) = √19411200 ≈ 4405.8; PPI = 4405.8 / 27 ≈ 163.2 PPI.
What is dot pitch and why does it matter?
Dot pitch is the physical distance between the centers of adjacent pixels, measured in millimeters. It equals 25.4 / PPI. A smaller dot pitch means pixels are closer together, producing a sharper, more detailed image. It is commonly used in display specifications and engineering contexts. A 27-inch 4K monitor has a dot pitch of about 0.156 mm, while a 27-inch 1080p monitor has a dot pitch of about 0.311 mm.
What does the reverse mode do?
The reverse mode estimates the screen resolution if you know the desired PPI and the screen diagonal size. It assumes a 16:9 aspect ratio and computes the expected width and height in pixels. This is useful for display design, app UI planning at a target pixel density, or verifying device specifications.
Why does higher PPI make a screen look sharper?
Higher PPI means more pixels packed into each inch, so each individual pixel is smaller and less visible to the naked eye. At typical viewing distances (50–70 cm for phones, 50–80 cm for monitors), the human eye can resolve about 300 PPI. Apple's Retina displays target around 220–460 PPI depending on the viewing distance of the device.
How do I use the device presets?
Click any preset button (e.g., "iPhone 15 Pro" or "4K Monitor 27"") and the width, height, and diagonal fields will populate automatically. The PPI and other results will update immediately. You can then manually adjust any field to explore custom configurations.
What is the aspect ratio calculation based on?
The aspect ratio is simplified using the greatest common divisor (GCD) algorithm applied to the width and height in pixels. For example, 3840×2160: GCD(3840, 2160) = 480; 3840/480 = 8, 2160/480 = 4.5 — but since pixels are integers, the ratio shows as 16:9 for standard 4K. The displayed ratio reflects the exact pixel ratio, not a rounded standard name.
Can I use this calculator for print DPI?
Technically yes — the math is the same. If you know the print resolution in dots (pixels) and the physical print size in inches, entering those values will give you the print DPI. However, the standard print DPI targets differ from screen PPI: print typically requires 300 DPI for photo quality and 72–96 DPI for standard web/screen images.