Is a higher PPI always better?

Not on its own. PPI only matters relative to how far away you sit. A 55-inch 4K TV is only about 80 PPI, but viewed from three metres its pixels-per-degree easily clears the retina threshold, so you would never see the dots. A 6-inch phone needs 400+ PPI to look as sharp at arm's length. Past the point where pixels are no longer resolvable at your viewing distance, more PPI buys you nothing but a smaller battery — that is why the viewing-distance field here matters more than the raw number.

What is a retina display, exactly?

Retina is Apple's marketing term for a screen dense enough that, at a typical viewing distance, a person with normal 20/20 vision cannot make out individual pixels. The physics behind it is angular resolution: the human eye resolves down to roughly one arc-minute, which works out to about 60 pixels per degree of vision. This tool computes that pixels-per-degree value from your PPI and the distance you enter, so the verdict reflects your actual setup rather than a fixed number printed on a box.

How much does 4K PPI change across screen sizes?

A lot — the resolution is fixed at 3840×2160, so PPI is just that diagonal divided by the screen size. On a 27-inch monitor 4K is about 163 PPI (crisp, often needing UI scaling). On a 32-inch monitor it drops to roughly 138 PPI. On a 55-inch TV it is only about 80 PPI. Same pixel count, very different density, which is why a 4K 27-inch panel looks razor sharp on a desk while a 4K TV looks fine only because you sit far from it. Type each diagonal in and watch the PPI move.

What is dot pitch and how does it relate to PPI?

Dot pitch is the centre-to-centre distance between two neighbouring pixels, given here in millimetres. It is simply the inverse of density: dot pitch = 25.4 mm ÷ PPI. A 100 PPI monitor has a 0.254 mm dot pitch; a 460 PPI phone is down near 0.055 mm. Older CRT and LCD spec sheets quoted dot pitch instead of PPI, so this lets you compare a modern panel against a legacy spec without converting in your head.

Does this assume square pixels?

Yes. The physical width and height are derived by splitting the diagonal in the same ratio as the pixel dimensions, which is exact only when pixels are square — true for essentially every modern LCD, OLED and the displays in the preset list. A handful of unusual panels (some older plasma screens, certain pro video monitors) use non-square pixels, in which case the physical dimensions here will be slightly off, though the PPI along the diagonal stays correct.

Choose between two monitors before you buy

You are deciding between a 27-inch 1440p panel and a 27-inch 4K one. Punch in 2560×1440 @ 27" (≈109 PPI) and 3840×2160 @ 27" (≈163 PPI) and you immediately see the 4K is half again as dense. Then drop your desk viewing distance (about 24 inches) into the retina field: the 4K clears 60 px/° comfortably while the 1440p sits just under it, which tells you the 4K is worth it on a desk but you will want OS scaling on at 163 PPI.

Pick a CSS device-pixel-ratio target

You are tuning responsive breakpoints and need to know which devices are @2x or @3x. Fill in a phone's native resolution and diagonal to read its true PPI, compare it against the ~160 PPI baseline a CSS pixel assumes, and you can reason about whether a layout that looks crisp on your desktop will look soft or oversharp on a given handset.

Compare your phone screen against a friend's

Two phones both claim "stunning display". Enter each one's resolution and screen size, and the PPI and pixels-per-degree at 12 inches settle the argument with numbers. A 1080×2400 6.5-inch panel lands around 405 PPI; a 1179×2556 6.1-inch lands near 460 — both are retina at reading distance, so the visible difference is smaller than the spec sheet implies.

Size UI assets for a kiosk or signage screen

You are building a touchscreen kiosk on a 32-inch 1080p panel. Its PPI is only about 69, and users stand close, so 1 CSS pixel is physically large. Reading that low PPI tells you to bump font sizes and tap targets well above your desktop defaults so text does not look chunky and buttons are comfortable to hit at arm's length.

Verify a panel's advertised spec

A listing says "5K 27-inch, 218 PPI". Enter 5120×2880 @ 27" and confirm it really is ≈218 PPI before you trust the rest of the spec. If the numbers do not line up, the listing is mixing up resolution or size, and you have caught it before checkout.

PPI Calculator — pixel density, dot pitch, physical size & retina check

Pixel density, dot pitch, physical size, aspect ratio & a retina check from resolution + diagonal — all in your browser

Runs locally
Category Calculator
Best for Getting a realistic range before a purchase, plan, workout, or schedule decision.

Quick fill a known device

Horizontal resolution (px)

Vertical resolution (px)

Diagonal size (inches)

Pixels per inch (PPI)

91.8

Aspect ratio

16:9

Dot pitch

0.2767 mm

Physical size

20.92 × 11.77 in · 53.13 × 29.89 cm

Viewing distance (in)

Pixels per degree32

Not retina-class at this distance (≥ 60 px/° is the threshold where individual pixels stop being resolvable)

What this tool does

Type a screen's horizontal and vertical resolution plus its diagonal size in inches, and this calculator works out the full geometry of the panel: pixels per inch (PPI), the dot pitch in millimetres, the physical width and height in both inches and centimetres, and the reduced aspect ratio (1920×1080 collapses to 16:9). It also answers the question marketing copy keeps dodging — is the screen "retina"? Instead of a flat PPI cutoff it computes pixels-per-degree at a viewing distance you pick, because retina is about angular resolution: a phone at 25 cm and a TV at 3 m can both be retina at wildly different densities. Cross 60 px/° and individual pixels stop being resolvable to a typical eye. One-click presets fill in the iPhone 15, MacBook Pro 14", a 27" 4K monitor, a 55" 4K TV and more so you can compare two panels in seconds, and the inputs live in the URL so a share link reproduces the exact screen. Everything runs locally — no resolution you enter ever leaves the page.

Tool details

Input: Text + Numbers; The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
Output: Live result + Copy + Preview; The result area focuses on usable output, with copy, download, or preview actions when supported.
Privacy: Browser-side processing; The main tool logic does not call an external API, so inputs normally stay in the current tab.
Save / share: Shareable URL state; Key settings are encoded in the URL so another person can reopen the same setup.
Performance budget: Initial JS <= 10 KB; No WASM budget is declared, keeping the tool quick to open on mobile.
Best fit: Calculator · Developer; Category and role tags drive related tools, internal links, and quick fit checks.

How to use

1. Input

Paste or drop your content into the tool panel.
2. Process

Click the button. All processing is local in your browser.
3. Copy / Download

Copy the result or download to disk in one click.

How PPI Calculator fits into your work

Use it for fast estimates, comparisons, and planning numbers before you make the final call.

Calculation jobs

Getting a realistic range before a purchase, plan, workout, or schedule decision.
Comparing scenarios by changing one input at a time.
Turning rough assumptions into a number you can discuss.

Calculation checks

Double-check units, dates, rates, and rounding assumptions.
Treat health, finance, tax, and legal outputs as planning aids, not professional advice.
Save the inputs that produced an important result so you can reproduce it later.

Good next steps

These links move the current task into a more complete workflow.

Real-world use cases

Choose between two monitors before you buy
You are deciding between a 27-inch 1440p panel and a 27-inch 4K one. Punch in 2560×1440 @ 27" (≈109 PPI) and 3840×2160 @ 27" (≈163 PPI) and you immediately see the 4K is half again as dense. Then drop your desk viewing distance (about 24 inches) into the retina field: the 4K clears 60 px/° comfortably while the 1440p sits just under it, which tells you the 4K is worth it on a desk but you will want OS scaling on at 163 PPI.
Pick a CSS device-pixel-ratio target
You are tuning responsive breakpoints and need to know which devices are @2x or @3x. Fill in a phone's native resolution and diagonal to read its true PPI, compare it against the ~160 PPI baseline a CSS pixel assumes, and you can reason about whether a layout that looks crisp on your desktop will look soft or oversharp on a given handset.
Compare your phone screen against a friend's
Two phones both claim "stunning display". Enter each one's resolution and screen size, and the PPI and pixels-per-degree at 12 inches settle the argument with numbers. A 1080×2400 6.5-inch panel lands around 405 PPI; a 1179×2556 6.1-inch lands near 460 — both are retina at reading distance, so the visible difference is smaller than the spec sheet implies.
Size UI assets for a kiosk or signage screen
You are building a touchscreen kiosk on a 32-inch 1080p panel. Its PPI is only about 69, and users stand close, so 1 CSS pixel is physically large. Reading that low PPI tells you to bump font sizes and tap targets well above your desktop defaults so text does not look chunky and buttons are comfortable to hit at arm's length.
Verify a panel's advertised spec
A listing says "5K 27-inch, 218 PPI". Enter 5120×2880 @ 27" and confirm it really is ≈218 PPI before you trust the rest of the spec. If the numbers do not line up, the listing is mixing up resolution or size, and you have caught it before checkout.

Common pitfalls

Comparing PPI numbers across very different screen types as if higher always wins. A phone and a TV live at different viewing distances, so pixels-per-degree, not raw PPI, is the fair comparison. Always set the distance field to your real setup.
Entering the screen's physical width or height instead of the diagonal. The size field expects the diagonal (the number TVs and laptops are marketed by). Putting the width in there inflates the PPI and throws off every derived value.
Mixing the resolution axes up, e.g. typing a portrait phone as 2556×1179. The aspect ratio flips but PPI is unaffected since it uses the diagonal — still, fix the orientation so the physical width and height come out the right way round.

Privacy

Every value here — PPI, dot pitch, physical size, aspect ratio and the pixels-per-degree retina check — is computed by plain JavaScript in your browser tab. No resolution or screen size you enter is sent anywhere, there is no logging, and there is no external API call. The one thing to note: the shareable URL encodes your inputs in the query string (e.g. ?w=1920&h=1080&d=24), so if you paste a share link somewhere the destination server's access log will record those numbers. Screen specs are not sensitive, so for normal use this is harmless — but if you would rather not, copy the result text instead of sharing the link.

FAQ

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PPI Calculator — pixel density, dot pitch, physical size & retina check

What this tool does

Tool details

How to use

1. Input

2. Process

3. Copy / Download

How PPI Calculator fits into your work

Calculation jobs

Calculation checks

Good next steps

Real-world use cases

Choose between two monitors before you buy

Pick a CSS device-pixel-ratio target

Compare your phone screen against a friend's

Size UI assets for a kiosk or signage screen

Verify a panel's advertised spec

Common pitfalls

Privacy

FAQ

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