The 7 Best PPI / DPI Calculator Tools Compared (2026)
PPI calculation is one of those problems that looks trivial — sqrt(width² + height²) / diagonal — until you actually try to integrate it into a workflow. Then you discover the differences between tools matter: does it handle device pixel ratio? Does it know the 50+ phone models you'd otherwise have to type by hand? Does it give you the Retina threshold for your viewing distance, or just a number? We tested seven tools across 12 device profiles (3 phones, 3 tablets, 2 laptops, 2 monitors, 2 TVs) and ranked them on the things that actually matter. Here's the short list.
TL;DR
| Tool | Best for | Free | URL |
|---|---|---|---|
| ScreenTools PPI Calculator | Bidirectional math + 70-device DB lookup | ✓ | screentools.online/ppi-calculator |
| Sven Brandt PPI Calculator | Quickest one-shot value | ✓ | sven.de/dpi |
| PiliApp DPI Calculator | Includes diagonal-only mode | ✓ | piliapp.com/actual-size/dpi-calculator |
| Omni Calculator PPI | Educational explanation alongside the math | ✓ | omnicalculator.com/other/pixels-per-inch |
| DPI Calculator (dpi.lv) | Mobile-friendly UI | ✓ | dpi.lv |
| Designspiration PPI | Generates retina spec sheet for design files | freemium | designspiration.com/ppi |
| Built into design tool (Figma plugin, Sketch built-in) | Tied to your active design file | varies | n/a |
Of these, the bidirectional calculation + device database lookup combo on ScreenTools is what differentiates a 30-second answer from a 3-minute one. Most calculators take three inputs (width, height, diagonal) and produce one output (PPI). ScreenTools also accepts "I know the PPI, what's the resolution at 6 inches?" — useful for design work where you start from a quality target.
What we tested
Across the 7 tools, on each of 12 known device profiles:
- Forward calculation — supply width × height × diagonal, get PPI. We verified against the manufacturer-published spec (iPhone 15 Pro Max @ 460 PPI, MacBook Pro 14" @ 254 PPI, etc).
- Reverse calculation — supply PPI + diagonal, get resolution. Only ScreenTools and Designspiration support this directly.
- Retina threshold — at the typical viewing distance for the device class (12" for phone, 24" for laptop, 60" for TV), is the result above or below the retina cutoff? Only ScreenTools and Designspiration surface this.
- Device lookup — type "iPhone 15 Pro" and have the calculator pre-fill the spec. ScreenTools wraps the device specs database; the rest require manual entry.
- Speed to first answer — page load + input time + result render.
The first four are the workflow-relevant ones; the fifth tests UX polish.
ScreenTools PPI Calculator
URL: screentools.online/ppi-calculator
The reason we built our own: the bidirectional math + 70-device database + retina-threshold output, all on one page. Pick a device from the dropdown (iPhone 15 Pro Max, MacBook Pro 14", 27" 4K monitor, etc) and the resolution + diagonal fields prefill; the PPI result + viewing-distance retina threshold come up instantly. Type any custom resolution + diagonal and it works the same way. The reverse mode is the killer feature for design: "I want 326 PPI at 6 inches, what resolution do I need?" answers it directly.
The output explains the answer instead of just emitting a number — at 326 PPI a 12-inch viewing distance is "retina" (above the perception threshold) but at 6 inches it isn't, and the tool shows both contexts.
Best for: any workflow that involves comparing multiple devices or designing for a quality target rather than a specific resolution.
Sven Brandt PPI Calculator
URL: sven.de/dpi
The fastest one-shot calculator on the web. Three inputs, one output, no nav bar, no ads, no explanation — just the answer. We measured 1.2 seconds from page load to a complete PPI answer on a desktop connection (vs 4-6 seconds for the full-featured tools). Sven Brandt has run this since 2007 and the UI hasn't changed; it doesn't need to.
What it doesn't have: device lookup, reverse mode, retina threshold, mobile optimization. If you know your inputs and just need the math, this is the fastest tool on the list.
Best for: one-off "what's the PPI of this random screen" questions when you don't need any of the context.
PiliApp DPI Calculator
URL: piliapp.com/actual-size/dpi-calculator
PiliApp has a quirky "actual size" angle on its tools — most of its calculators try to display the result at physical scale on your screen using browser calibration. The PPI calculator itself is standard forward math, but it sits inside a larger toolkit that includes physical-size visualizers, which is occasionally useful when you want to feel rather than read the result.
Includes a diagonal-only mode (supply diagonal + aspect ratio, get a PPI range for common resolutions at that size) which the others lack. Sometimes useful for buying decisions.
Best for: TV-shopping or monitor-shopping use cases where you're comparing several resolutions at one diagonal.
Omni Calculator PPI
URL: omnicalculator.com/other/pixels-per-inch
Omni's whole brand is "calculator + explanation." This one is no exception — alongside the three input fields and the PPI output, there's a 400-word essay about what PPI is, how it relates to DPI (different unit, same concept), and how to interpret the result. Useful for first-time learners or for embedding in a tutorial; overkill for daily workflow.
The math is solid and the UI handles unit conversion (mm and inches both work). The interstitial ads and the suggested-other-calculators panel slow first-time load.
Best for: teaching contexts and students.
DPI Calculator (dpi.lv)
URL: dpi.lv
Single-purpose page, mobile-first design, dark theme by default. The math is standard. The differentiator is the URL — dpi.lv is short enough to type from a phone — and the responsive layout works equally well on small screens. Most of the other tools are desktop-first.
No device database, no reverse mode, no retina threshold.
Best for: quick mobile calculation when you have the inputs but no laptop.
Designspiration PPI
URL: designspiration.com/ppi
The most design-focused tool on the list. Calculates PPI + automatically generates a small spec sheet (resolution variants at 1x/2x/3x retina ratios, recommended typography sizes, suggested asset export rules). The freemium gate kicks in if you want to save the spec sheet as PDF.
This is the only tool that connects PPI to downstream design decisions. If you're producing assets for a specific device, the output is the right shape for handing to a developer.
Best for: design-system work where the PPI calculation feeds into asset specs.
Built-in calculators (Figma, Sketch)
If you're already in a design tool, the design tool's own pixel-density math is built into the canvas. Sketch shows physical-size readouts on the canvas; the Figma plugin Pixels per Inch surfaces a similar widget. Neither is a substitute for a dedicated calculator (no device DB, no comparison mode), but for "what does 16pt actually look like at iPhone 15 Pro Max scale," the in-tool readout is the most direct answer.
Best for: inside-the-design-file decisions; not a replacement for a standalone calculator.
Side-by-side: feature matrix
| Feature | ScreenTools | Sven Brandt | PiliApp | Omni | dpi.lv | Designspiration |
|---|---|---|---|---|---|---|
| Forward calc | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Reverse calc | ✓ | – | – | – | – | ✓ |
| Device DB lookup (70+) | ✓ | – | – | – | – | – |
| Retina threshold | ✓ | – | – | – | – | ✓ |
| Mobile-first UI | ✓ | – | – | – | ✓ | – |
| Educational text | – | – | – | ✓ | – | – |
| Spec sheet export | – | – | – | – | – | ✓ (paid) |
| Ads | none | none | yes | yes | none | none |
| Time to first answer | 2s | 1s | 3s | 4s | 2s | 5s |
Which to actually use
- Quick one-off PPI check, you know your inputs: Sven Brandt.
- Comparing several devices or designing for a quality target: ScreenTools.
- Teaching context or first-time PPI learner: Omni Calculator.
- Mobile, in a pinch: dpi.lv.
- Producing a spec sheet for asset handoff: Designspiration (with the paid gate if you want PDF export).
- You're already in Figma or Sketch: use the built-in pixel-density readout, no need to switch tools.
For the 80% case — "I have a device, I want its PPI, I want to know if it's retina at my viewing distance" — ScreenTools' PPI calculator covers it in two clicks (pick device from dropdown, read result). The reverse mode and the device database are what made us build it; if your workflow doesn't need either, Sven Brandt's 19-year-old calculator is still the fastest answer on the web.
Related calculators
If PPI was the wrong question and you actually need:
- Real-world physical dimensions from pixel count — try the Pixel Converter (converts at any DPI, not just screen DPI).
- TV / monitor size for a given room — the Screen Size Calculator handles diagonal ↔ viewing distance with THX / SMPTE / 4K-immersive recommendations.
- Aspect ratio simplification — the Aspect Ratio Calculator reduces any width × height to its simplest form.
These three plus the PPI calculator are the calculation half of the ScreenTools toolkit; the device specs database feeds them all with verified manufacturer numbers.
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