The Screen Resolution Calculator computes PPI (Pixels Per Inch) and compares monitor resolutions.
Two modes: calculate PPI from resolution and screen size, and compare resolutions from HD to 8K at various screen sizes. Presets for iPhone, iPad, MacBook, monitors, and TVs.
Calculator information
📋 How to use this calculator
- Choose mode: calculate PPI or compare two resolutions.
- To calculate PPI, enter horizontal x vertical resolution (e.g., 1920 x 1080) and the screen diagonal (inches).
- Read the PPI value; above 220 PPI is considered Retina-class at a normal viewing distance.
- For comparison, pick two resolutions (HD, FHD, QHD, 4K, 8K) and the diagonal of each display.
- Review the differences in total pixels, bandwidth requirements, and GPU demands.
- Use device presets such as iPhone, iPad, MacBook, or a 27-inch 4K monitor for a quick sanity check.
🧮 Pixels Per Inch (PPI)
PPI = sqrt(W^2 + H^2) / D
- W: horizontal resolution in pixels
- H: vertical resolution in pixels
- D: screen diagonal in inches
- sqrt(W^2 + H^2): diagonal in pixels (Pythagoras)
Apple defines a 'Retina' display as one whose PPI is high enough that individual pixels are not visible at a normal viewing distance: ~300 PPI for a smartphone (~10 in), ~220 PPI for a laptop (~16 in).
💡 Worked example: 27-inch monitor at 4K UHD (3840 x 2160)
Given:- Horizontal resolution: 3840 pixels
- Vertical resolution: 2160 pixels
- Screen diagonal: 27 inches
Steps:- Diagonal in pixels: sqrt(3840^2 + 2160^2) = sqrt(14,745,600 + 4,665,600) = sqrt(19,411,200) ~ 4,405.5
- PPI: 4,405.5 / 27 ~ 163.18 PPI
- Total pixels: 3840 x 2160 = 8,294,400 pixels (~8.3 megapixels)
- Bandwidth at 60 Hz, 8-bit RGB: 3840 x 2160 x 60 x 24 / 8 ~ 1.49 GB/s, requires HDMI 2.0/DP 1.2
Result: A 27-inch 4K monitor has a pixel density of 163 PPI, below the Retina threshold (220 PPI), but sharp enough for productivity at a typical sitting distance of 24-28 inches.
❓ Frequently asked questions
What is the minimum PPI for a sharp-looking screen?
It depends on viewing distance. For smartphones (10-12 inches), a minimum of 300 PPI. For tablets (16 inches), 220-260 PPI. For desktop monitors (24-32 inches), 110-150 PPI is generally enough, with 218 PPI (4K 27-inch or 5K 27-inch) serving as the Retina baseline. For a living-room TV (6-10 feet), 4K on a 55-inch set already exceeds the eye's resolving power.
Is 4K always better than 1440p?
Not automatically. 4K (3840 x 2160) has 4x the pixels of FHD and 2.25x more than QHD (2560 x 1440). However it requires a far stronger GPU for gaming, HDMI 2.1 or DP 1.4 cabling for 120 Hz, and a sufficiently large screen (at least 27 inches) to make the sharpness difference noticeable. For 24-27 inch gaming monitors, 1440p is often the performance-visual sweet spot.
What is the difference between PPI and DPI?
PPI (Pixels Per Inch) measures pixel density on a digital display. DPI (Dots Per Inch) measures ink-dot density on physical print. The terms are often used interchangeably, but DPI applies to printers (300 DPI is the standard for book printing) while PPI applies to displays. Image dimensions for web are typically expressed in 72-96 PPI.
How much bandwidth does 4K 144Hz HDR require?
4K 3840 x 2160 at 144 Hz with 10-bit RGB requires ~31 Gbps, exceeding HDMI 2.0's capacity (18 Gbps) but fitting within HDMI 2.1 (48 Gbps) and DisplayPort 1.4 with DSC (Display Stream Compression). For an uncompressed experience, use DisplayPort 2.0/2.1 (UHBR 20: 80 Gbps), already available on modern 2024-2025 GPUs.
Does HiDPI scaling make icons smaller on a 4K display?
Quite the opposite - HiDPI scaling preserves the physical size of icons as on a lower-resolution display, but with much sharper edges because they are rendered at native pixels. Windows offers 100%-300% scaling (default 150% on 13-15 inch 4K laptops). macOS automatically uses 2x scaling on Retina displays. Without scaling, icons on a 27-inch 4K display would appear extremely small.
📚 Sources & references
Last updated: May 11, 2026