PPI Calculator
Calculate pixels per inch for any screen. Enter resolution and size to get PPI, aspect ratio, total pixels, and display classification.
PPI (Pixels Per Inch) measures how densely pixels are packed on a screen. Higher PPI means sharper text, crisper images, and less visible pixelation. This calculator takes a screen's resolution and diagonal size and returns the PPI, total pixel count, aspect ratio, physical dimensions, and a density classification. It runs entirely in your browser.
About PPI Calculator
How PPI Is Calculated
PPI equals the diagonal resolution in pixels divided by the diagonal screen size in inches, where the diagonal resolution comes from the Pythagorean theorem: PPI = sqrt(width_px^2 + height_px^2) / diagonal_inches.
Worked example (24" 1080p monitor): A 1920 x 1080 resolution gives a diagonal of sqrt(1920^2 + 1080^2) = sqrt(3,686,400 + 1,166,400) = sqrt(4,852,800) = 2,202.9 pixels. Dividing by the 24-inch diagonal: 2,202.9 / 24 = 91.8 PPI. Total pixel count is 1920 x 1080 = 2,073,600 (about 2.1 megapixels), and the physical width is 1920 / 91.8 = 20.9 inches (53.1 cm), with a height of 11.8 inches (29.9 cm).
| Display | Resolution | Diagonal | Diagonal Pixels | PPI |
|---|---|---|---|---|
| 24" office monitor | 1920 x 1080 | 24" | 2,203 | 91.8 |
| 27" 4K monitor | 3840 x 2160 | 27" | 4,406 | 163.2 |
| 14" MacBook Pro | 3024 x 1964 | 14.2" | 3,605 | 253.9 |
| iPhone 15 Pro | 2556 x 1179 | 6.1" | 2,815 | 461.5 |
| iPad Pro 12.9" | 2732 x 2048 | 12.9" | 3,415 | 264.7 |
A 24" 1080p monitor has 92 PPI, while an iPhone 15 Pro packs 461 PPI into a 6.1" screen. That 5x density difference is why text looks razor-sharp on phones but can appear slightly soft on large desktop monitors.
PPI Density Classifications
| Classification | PPI Range | Typical Devices | Pixel Visibility |
|---|---|---|---|
| Low density | Under 100 | Large desktop monitors at 1080p (27"+) | Individual pixels clearly visible |
| Standard density | 100-149 | 24" 1080p monitors, older laptops | Pixels visible if you look closely |
| High density | 150-199 | 27" 4K monitors, some tablets | Pixels hard to see at arm's length |
| Retina / HiDPI | 200-299 | MacBooks, iPad Pro, Surface laptops | Pixels invisible at normal distance |
| Super high density | 300-399 | Flagship phones (Samsung Galaxy S24) | Indistinguishable from print |
| Ultra high density | 400+ | iPhone Pro models, Sony Xperia | Beyond human visual acuity at any distance |
Apple coined "Retina display" to mean pixels are too small to see at the typical viewing distance. For phones held at 25-30 cm, that threshold is about 300 PPI. For laptops at 45-60 cm, about 220 PPI. For desktop monitors at 60-80 cm, about 150 PPI.
PPI vs DPI vs Device Pixel Ratio
These terms are related but distinct, and they are often confused.
| Term | Meaning | Context |
|---|---|---|
| PPI (Pixels Per Inch) | Physical pixel density of a screen | Display hardware specs |
| DPI (Dots Per Inch) | Ink dots per inch in print | Printers and print design |
| Device Pixel Ratio (DPR) | Physical pixels / CSS pixels | Web development (window.devicePixelRatio) |
| Logical resolution | Resolution the OS reports to apps | macOS "looks like 1800x1169" on MacBook Pro |
A MacBook Pro 14" has 3024 x 1964 physical pixels but macOS reports a logical resolution of about 1512 x 982 at the default setting. That gives a DPR of 2x, meaning each CSS pixel is rendered with 4 physical pixels (2 x 2). Web developers use DPR to serve appropriately sized images. Check your current device's DPR with the Screen Resolution Checker.
Why PPI Matters for Designers
| Design Decision | How PPI Affects It |
|---|---|
| Image resolution | A 100x100px image looks fine at 96 PPI but blurry on a 2x Retina display - serve 200x200px for crisp rendering |
| Font rendering | Fonts on low-PPI screens need hinting (subpixel adjustments) to look sharp - high-PPI screens render any font smoothly |
| Icon design | 1px borders and fine details disappear on low-PPI screens - design for the lowest target PPI |
| Print preparation | A 300 PPI image printed at 100% looks the same as on a 300 PPI screen, but a 96 PPI screen image prints at roughly 1/3 the quality |
| UI element sizing | A 44px touch target is 0.46" on a 96 PPI screen but only 0.10" on a 460 PPI phone - use physical size, not just pixels |
Common Screen Resolutions and Their PPI
| Resolution Name | Pixels | PPI at 24" | PPI at 27" | PPI at 32" |
|---|---|---|---|---|
| Full HD (1080p) | 1920 x 1080 | 91.8 | 81.6 | 68.8 |
| QHD (1440p) | 2560 x 1440 | 122.4 | 108.8 | 91.8 |
| 4K UHD | 3840 x 2160 | 183.6 | 163.2 | 137.7 |
| 5K | 5120 x 2880 | 244.8 | 217.6 | 183.6 |
This is why a 27" 4K monitor (163 PPI) looks noticeably sharper than a 27" 1440p (109 PPI), and why the Apple Studio Display at 27" 5K (218 PPI) achieves true Retina quality at desktop viewing distances.
Print PPI (DPI) Requirements
| Print Type | Required DPI | Pixels Needed for A4 (210 x 297mm) |
|---|---|---|
| Newspaper / web use | 72-96 | 595 x 842 |
| Standard print (flyers, books) | 300 | 2,480 x 3,508 |
| High-quality print (photo books) | 300-600 | 2,480 x 3,508 minimum |
| Large format (posters, banners) | 150 | 1,240 x 1,754 (A4 equivalent) |
The standard for professional print is 300 DPI. Images below this threshold appear pixelated when printed. For large-format prints viewed from a distance (posters, banners), 150 DPI is usually sufficient.
Viewing Distance and the Retina Threshold
Apple's original Retina claim was that 300 PPI is indistinguishable from print at 10-12 inches (25-30 cm), which is how people hold phones. The underlying maths comes from the angular resolution of the human eye - roughly 1 arcminute, or about 1/60th of a degree. At a given viewing distance d, the minimum pixel spacing that the eye can resolve is d * tan(1/60 degrees). Converting that to PPI gives the approximate thresholds below.
| Device Type | Typical Viewing Distance | Retina PPI Threshold | Real-World Example |
|---|---|---|---|
| Smartphone | 10-12 in (25-30 cm) | ~300 PPI | iPhone 16 Pro at 460 PPI clears the threshold with room to spare |
| Tablet | 15-18 in (38-45 cm) | ~260 PPI | iPad Pro 12.9" at 265 PPI sits exactly on the line |
| Laptop | 20-24 in (50-60 cm) | ~220 PPI | MacBook Pro 14" at 254 PPI comfortably exceeds it |
| Desktop monitor | 24-32 in (60-80 cm) | ~160 PPI | Apple Studio Display at 218 PPI is Retina class for its distance |
| TV (55") | 8-10 ft (2.4-3 m) | ~40 PPI | A 4K 55" TV at about 80 PPI is well above the threshold |
This is why a phone appears to need far more PPI than a TV to look equally sharp. Raise the viewing distance and the same pixel spacing subtends a smaller angle, so fewer pixels per inch are needed to fool the eye.
PPI Bands Used by Android and Web Standards
The Android platform groups devices into density buckets (ldpi, mdpi, hdpi, xhdpi, xxhdpi, xxxhdpi) so designers can provide the right asset for each class. Web browsers expose a similar concept through the CSS resolution media query and the devicePixelRatio property.
| Android Bucket | Target PPI | DPR | Asset Scale | Example Devices |
|---|---|---|---|---|
| mdpi (baseline) | 160 | 1.0x | 1x | Older budget tablets |
| hdpi | 240 | 1.5x | 1.5x | Mid-range Android phones |
| xhdpi | 320 | 2.0x | 2x | Pixel 7a, iPhone non-Pro |
| xxhdpi | 480 | 3.0x | 3x | iPhone 15 Pro, Galaxy S24 |
| xxxhdpi | 640 | 4.0x | 4x | Some foldables and flagship pixel art |
The Material Design guidelines and Apple's Human Interface Guidelines both anchor sizing to a 160 PPI mdpi baseline called a "density-independent pixel" (dp) or "point" respectively. A 24 dp icon renders as 24 physical pixels at mdpi, 48 at xhdpi, and 72 at xxhdpi, so tap targets stay the same physical size across devices.
Common Mistakes When Working With PPI
- Confusing diagonal with width. A 27" monitor has a 27-inch diagonal, not a 27-inch width. Use the formula's diagonal directly, do not derive PPI by dividing horizontal pixels by horizontal inches unless you measure the physical width yourself.
- Using the logical resolution instead of the native resolution. A MacBook Pro 14" has 3024 x 1964 native pixels but macOS reports "looks like 1512 x 982" by default. Always feed the native resolution into the calculator to get the true PPI.
- Assuming more PPI is always better. On a desktop monitor at arm's length, anything beyond about 220 PPI is wasted on the user and costs GPU performance - 4K gaming on a 27" screen is sharper than 1440p but demands roughly 2.25x the pixels to push.
- Treating PPI as a proxy for image quality. PPI only measures pixel density. Colour accuracy, contrast ratio, refresh rate, and HDR support all matter for perceived image quality and are independent of PPI.
- Mixing PPI and DPI when preparing print. 300 DPI is a print standard (ink dots per inch), while PPI is a screen metric. A 300 PPI screen image is not automatically print-ready - check the output dimensions in inches at 300 DPI first.
For checking your current device's screen resolution and DPR, the Screen Resolution Checker reads those values directly. For mapping image dimensions to different aspect ratios, try the Aspect Ratio Calculator. All calculations run in your browser.
Sources
- Apple - iPhone 16 Pro Technical Specifications
- Apple - MacBook Pro 14-inch Technical Specifications
- Apple Human Interface Guidelines - Layout and Points
- Android Developers - Support Different Pixel Densities
- Material Design 3 - Layout and Spacing (density-independent pixels)
- MDN Web Docs - Window.devicePixelRatio
- W3C - CSS Values and Units (absolute lengths)
Frequently Asked Questions
What is PPI and why does it matter?
PPI (Pixels Per Inch) measures how densely pixels are packed on a screen. Higher PPI means sharper text and images because individual pixels become invisible to the eye. It matters for designers who need to know whether their designs will look crisp on different devices.
What PPI counts as Retina or HiDPI?
Apple considers a display "Retina" when pixels are small enough that the human eye cannot distinguish them at a normal viewing distance. For phones held close, this is around 300+ PPI. For laptops at arm's length, around 220+ PPI. For desktop monitors viewed from further away, 200+ PPI is considered high density.
How is PPI calculated?
PPI is calculated by dividing the diagonal resolution (in pixels) by the diagonal screen size (in inches). The diagonal resolution is found using the Pythagorean theorem on the horizontal and vertical pixel counts.
Does higher PPI always mean better quality?
Beyond a certain point, higher PPI provides no visible benefit since the human eye has a resolution limit. For phones, anything above 400 PPI is effectively indistinguishable. For desktop monitors, 150-200 PPI is considered very good for typical viewing distances.
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