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Screen Size Calculator

Enter your screen's diagonal and resolution to get PPI, physical dimensions, aspect ratio & megapixels instantly. Works for phones, tablets, laptops & monitors.

Quick Presets
Screen Diagonal15.6 inches
Resolution (pixels)
Width (px)
×
Height (px)
PPI Quality Rating
LowMediumHighVery HighExtreme
Screen Diagram (to scale)
Screen Size Calculator – Calculate PPI, pixel density, and physical dimensions for any display
📋 Table of Contents

What Is a Screen Size Calculator?

A screen size calculator computes a display's pixel density (PPI — pixels per inch), physical width and height in both inches and centimeters, aspect ratio, screen area, and total megapixels from two inputs: the diagonal size in inches and the resolution in pixels. These numbers matter when comparing displays, evaluating sharpness at a given viewing distance, or verifying that a screen's advertised size matches its actual physical measurements.

The diagonal measurement printed on the box tells you how big a screen feels, but PPI tells you how sharp it actually looks. A 24" monitor at 1920×1080 has a PPI of 91.79 — acceptable at arm's length. Scale the same resolution to a 15.6" laptop screen and PPI climbs to 141.21 — noticeably sharper. The same 1080p resolution on a 55" TV drops to just 40 PPI, which looks fine from a couch but blurry up close. All three of these numbers are individually calculated and verified.

How to Use This Calculator

  1. Use a quick preset — tap any device button to auto-fill diagonal and resolution for common phones, tablets, laptops, and monitors
  2. Or enter manually — type your screen's diagonal in inches (found on the box or spec sheet) and its resolution width × height in pixels
  3. Click "Calculate Screen Size" — results include PPI, physical dimensions (cm and inches), aspect ratio, screen area, and megapixel count
  4. Read the PPI bar — the quality rating shows where your display falls from Low to Extreme pixel density
  5. Check the diagram — an SVG shows the physical proportions of your screen to scale
📌 Finding your screen diagonal: Check the product box, manufacturer spec page, or look for a sticker on the back of the display. The diagonal is always measured corner to corner of the active display area — not including the bezel. For laptops, the "15-inch" in the product name is the rounded diagonal; the actual spec may be 15.6" or 15.3".

The PPI Formula Explained

PPI is the pixel count along the diagonal divided by the physical diagonal length. The diagonal pixel count uses the Pythagorean theorem on the resolution dimensions:

PPI = √(width_px² + height_px²) ÷ diagonal_inches Physical dimensions (from diagonal + aspect ratio): height_in = diagonal ÷ √(1 + (width_px/height_px)²) width_in = (width_px/height_px) × height_in Aspect ratio: GCD-reduced form of width_px : height_px Megapixels = (width_px × height_px) ÷ 1,000,000 Worked example — 15.6" laptop, 1920×1080 (Full HD): Diagonal pixels = √(1920² + 1080²) = √4,852,800 = 2,202.91 PPI = 2,202.91 ÷ 15.6 = 141.21 ppi Height (in) = 15.6 ÷ √(1 + (16/9)²) = 7.6481 in = 19.43 cm Width (in) = (16/9) × 7.6481 = 13.5966 in = 34.54 cm Area = 13.5966 × 7.6481 = 103.99 in² Megapixels = (1920 × 1080) ÷ 1,000,000 = 2.07 MP Aspect ratio = 1920:1080 reduced = 16:9
📌 Verify with this calculator: Enter diagonal 15.6, width 1920, height 1080 — you will get exactly PPI 141.21, width 34.54 cm, height 19.43 cm, area 670.89 cm², aspect ratio 16:9, and 2.07 MP. These match the formula box above exactly.

PPI Quality Tiers — What the Numbers Mean

PPI thresholds are relative to viewing distance. The commonly cited "Retina" threshold — where individual pixels are indistinguishable at normal use distance — isn't a fixed number. Apple uses ~227 PPI for phones (held at ~25 cm) and ~220 PPI for laptops (used at ~50 cm). For reference, the ranges below describe typical quality perception at each device's standard viewing distance:

PPI RangeQuality LabelTypical DevicePerception
Below 72Very LowOld CRT monitors, projectorsPixels visible even at normal distance
72–96LowLarge TVs (55"+), large monitors at FHDFine from 2m+, pixelated up close
96–150Medium24–27" FHD monitors, budget laptopsGood for everyday work; slight pixel awareness
150–227High (Retina-class)15.6" FHD laptops, QHD monitors, tabletsSharp at normal viewing distance
227–400Very HighMost modern smartphones, iPad ProPixels indistinguishable at typical use
400+ExtremeFlagship phones, VR headsetsExceeds human eye resolution limit

Reference: RTINGS — What Is Pixel Density and PPI?

Common Screen Reference Table

Every row below is independently calculated using the PPI formula. No row is estimated or interpolated:

DeviceDiagonalResolutionPPIW × H (cm)AR
Compact flagship phone6.1"1170×2532457.256.5×14.1 cm195:422
Large flagship phone6.8"1440×3088501.077.3×15.7 cm90:193
iPad Pro 11"11.0"1668×2388264.8116.0×22.9 cm139:199
iPad Pro 12.9"12.9"2048×2732264.6819.7×26.2 cm512:683
MacBook Air 13"13.3"2560×1600226.9828.6×17.9 cm8:5
Laptop 15.6" FHD15.6"1920×1080141.2134.5×19.4 cm16:9
Laptop 15.6" QHD15.6"2560×1440188.2834.5×19.4 cm16:9
Monitor 24" FHD24.0"1920×108091.7953.1×29.9 cm16:9
Monitor 27" QHD27.0"2560×1440108.7959.8×33.6 cm16:9
Monitor 27" 4K27.0"3840×2160163.1859.8×33.6 cm16:9
Monitor 32" 4K32.0"3840×2160137.6870.8×39.8 cm16:9

Notice that the 15.6" FHD and 15.6" QHD laptops have identical physical dimensions (34.5×19.4 cm) — the screen size doesn't change, only the pixel density. Going from FHD to QHD on a 15.6" laptop pushes PPI from 141.21 to 188.28 — a 33% jump in sharpness at the cost of more GPU load and slightly lower battery life.

Aspect Ratios Explained

Aspect ratio is the proportional relationship between width and height, reduced to the simplest whole-number form. A 1920×1080 screen reduces to 16:9 (both divisible by 120). Here's what the common ratios look like and where they appear:

Aspect RatioDecimalCommon UsesNotes
4:31.33Old TVs, monitors, iPad non-ProMore square — good for documents
16:101.60MacBook, productivity monitorsTaller than 16:9 — extra vertical space
16:91.78HD/FHD/4K TVs, most laptops & monitorsGlobal standard for video content
21:92.33Ultrawide gaming/cinema monitorsImmersive; black bars on standard video
20:92.22Many Android flagshipsTaller phone form factor
19.5:92.17Modern iPhone lineupApple's standard phone aspect ratio since iPhone X (2017)
📌 Why monitors advertised as "27-inch" vary in actual dimensions: A 27" 16:9 monitor measures 59.8×33.6 cm physically. A 27" 21:9 ultrawide is physically wider and shorter — same diagonal, completely different proportions. Always check the aspect ratio when comparing two displays with the same diagonal.

Resolution Standards — From HD to 8K

NameResolutionMegapixelsCommon Use
HD (720p)1280×7200.92 MPBudget phones, streaming
Full HD (1080p)1920×10802.07 MPLaptops, monitors, TVs — most common
QHD / 2K (1440p)2560×14403.69 MPGaming monitors, mid-range laptops
4K UHD3840×21608.29 MPPremium monitors, TVs, professional video
5K5120×288014.75 MPApple Studio Display, iMac
8K UHD7680×432033.18 MPHigh-end TVs, professional production

4K has exactly 4× the pixels of 1080p (8.29 MP vs 2.07 MP — derived from 3840/1920 = 2, squared = 4). That's why 4K content looks noticeably sharper than 1080p at the same screen size — four times as many pixels packed into the same physical area. Reference: Consumer Technology Association (CTA) — 4K Ultra HD Standards

5 Tips for Choosing a Display Based on These Numbers

  • Match PPI to your viewing distance. At a typical laptop distance (50–60 cm), 141 PPI (15.6" FHD) is comfortably sharp for most users. At monitor distance (60–80 cm), 91 PPI (24" FHD) works fine. At TV distance (2m+), even 40 PPI appears smooth. Higher is better, but only up to the point your eyes can perceive at your actual use distance.
  • Same resolution, different size = different PPI. A 27" QHD monitor (108.79 PPI) and a 15.6" QHD laptop (188.28 PPI) both display 2560×1440 pixels, but the laptop screen is nearly 73% sharper per inch. If you're buying a secondary monitor to match your laptop, look for PPI that's within 20–30% of your laptop's to avoid jarring sharpness differences.
  • 4K makes more sense smaller. A 27" 4K monitor hits 163.18 PPI — genuinely sharp at desktop distance. A 32" 4K drops to 137.68 PPI — still good, but the sharpness advantage over QHD shrinks. For 55"+ TVs viewed from 2m, 4K is mostly imperceptible beyond 1080p without close-up scrutiny.
  • Physical dimensions matter as much as diagonal. A 24" 16:9 monitor measures 53.1×29.9 cm. A 24" 21:9 ultrawide at the same diagonal would be physically wider and shorter. Always convert diagonal to width × height (cm) when planning desk space or multi-monitor setups — the diagonal alone doesn't tell you how much room the screen physically occupies.
  • Check the aspect ratio before buying for specific workflows. Video editors and filmmakers benefit from ultrawide (21:9) for timeline visibility. Programmers and writers often prefer 16:10 for extra vertical screen space. Gamers split between 16:9 (universal compatibility) and 21:9 (immersive field of view). The PPI number doesn't capture these workflow differences — aspect ratio does.

Reference: RTINGS — How to Choose a Monitor

Frequently Asked Questions — Screen Size Calculator

PPI stands for pixels per inch — the number of pixels packed into each inch of your screen. Higher PPI means smaller, more closely spaced pixels, which produces a sharper image. A 15.6" laptop at 1920×1080 has 141.21 PPI. The same 1920×1080 on a 24" monitor drops to 91.79 PPI — noticeably less sharp up close. Whether you can actually see the difference depends on viewing distance: at 60 cm, most people can't distinguish pixels above ~200 PPI, which is why Apple calls that threshold "Retina."
Not necessarily — it depends on resolution and viewing distance. A 32" 4K monitor (137.68 PPI) looks sharp at a desk. But a 32" 1080p monitor would be only 68.84 PPI — noticeably soft at close range. Larger screens need proportionally higher resolution to maintain perceived sharpness. As a rough guide: if you're doubling the screen size, you need roughly 4× the pixel count (resolution squared) to maintain the same PPI.
Screen size is the physical diagonal measurement in inches — how large the panel is. Resolution is how many pixels it contains (e.g., 1920×1080). Two screens can have the same size but different resolutions, or the same resolution but different sizes. A 15.6" 1920×1080 laptop and a 24" 1920×1080 monitor contain exactly the same number of pixels — but the laptop's pixels are 141.21 PPI while the monitor's are 91.79 PPI, making the laptop sharper at close range.
4K contains 8.29 million pixels vs 1080p's 2.07 million — exactly 4× more, derived from doubling both dimensions. On a 27" monitor viewed at 60–70 cm, the jump from 81.59 PPI (27" FHD) to 163.18 PPI (27" 4K) is clearly visible and well worth it. On a 55" TV viewed from 2.5m, human visual acuity limits mean the improvement is much harder to perceive without sitting very close. The benefit of 4K is real but more pronounced at smaller screen sizes and closer viewing distances.
Measure from one corner of the active display area (the lit portion, not the bezel) to the diagonally opposite corner using a tape measure or ruler. Record in inches or convert cm to inches by dividing by 2.54. Alternatively, look up the model number on the manufacturer's spec page — the diagonal is always listed. For laptops, the marketing name ("15-inch MacBook") is usually rounded; the spec sheet shows the precise value (13.3" or 13.6" depending on the model).
Because aspect ratio determines how the diagonal is distributed between width and height. A 27" 16:9 monitor measures 59.8×33.6 cm — wider and shorter. A hypothetical 27" 4:3 monitor would measure about 54.4×40.8 cm — narrower and taller. Both have a 27" diagonal, but they look completely different side by side. This is why phone comparisons based on diagonal alone are misleading — a 6.7" phone with a tall 20:9 aspect ratio has a narrow, elongated screen that occupies less desk/pocket space than a 6.7" 16:9 screen would.

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