This PPI calculator computes pixel density — pixels per inch and dot pitch — from a screen’s resolution and diagonal size, the number that decides how sharp text and images actually look at your viewing distance.
Density = Resolution ÷ Size
PPI = √(w² + h²) ÷ diagonal: the pixel diagonal spread over the physical diagonal. Because both terms are diagonals, PPI is consistent at any aspect ratio, and it links straight to the TV Size question: the same 4K resolution is 91.8 PPI on a 24″ monitor (razor sharp at a desk) and 67 PPI on a 65″ TV (sharp from a couch). Sharpness is never resolution alone — it’s resolution per inch at your distance. Dot pitch, the center-to-center pixel spacing, is PPI’s reciprocal form (25.4 ÷ PPI mm), the spec older monitor datasheets quote. Part of our Other Calculators collection.
Worked Examples (Verified)
- 24″ 1080p monitor: √(1920² + 1080²) = 2,203 px ÷ 24 = 91.8 PPI, dot pitch 0.277 mm — the widget’s defaults, the workhorse desktop spec of a decade
- 27″ 1440p: 2,937 ÷ 27 = 108.8 PPI — the sweet-spot upgrade: visibly crisper text at the same desk distance
- 6.1″ phone at 1179 × 2556: ≈ 460 PPI — far past the ~300 threshold where 20/20 eyes stop resolving pixels at reading distance (the “Retina” insight)
- 55″ 4K TV: 4,409 ÷ 55 = 80.2 PPI — lower than the office monitor, and correctly so: it’s read from 6+ feet
The Distance Rule Behind Every Number
- Your eye resolves about 1 arcminute: a pixel disappears when PPI ≥ 3438 ÷ distance-in-inches. At 12 in (phone): ~286. At 24 in (desk): ~143. At 96 in (couch): ~36.
- Below the threshold, more PPI buys smoother type edges and scaling headroom, not visible sharpness — spend accordingly.
- Print flips the logic: 300 DPI is the photo standard because paper is examined at reading distance with no backlight forgiveness.
- Non-square pixels and PenTile subpixel layouts fudge the simple formula slightly; treat computed PPI as the honest nominal figure.
Related Tools
- TV Size Calculator — the diagonals themselves
- Aspect Ratio Calculator — the shape resolution lives in
- Other Calculators — the full collection
Frequently Asked Questions
How do you calculate PPI?
Divide the diagonal pixel count by the diagonal inches: PPI = √(width² + height²) ÷ diagonal. A 1920×1080, 24-inch screen: 2,203 ÷ 24 = 91.8 PPI.
What is a good PPI for a monitor?
At desk distance (~2 ft), ~110 PPI is visibly clean and ~140+ is crisp for text work: 27″ 1440p (108.8) is the popular floor, 27–32″ 4K (140–163) the premium tier. Below ~90 PPI at a desk, pixel structure shows in text.
Is higher PPI always better?
Only until pixels fall below your eye’s resolution at your distance (~1 arcminute). Past that, higher PPI costs GPU work, battery and money without visible return — which is why phones plateaued near 460–500 PPI and TVs can thrive at 65–90.
What is dot pitch vs PPI?
Two expressions of the same spacing: dot pitch is the millimeters between pixel centers (25.4 ÷ PPI), PPI the density. 91.8 PPI = 0.277 mm pitch. Small pitch = dense = same compliment.
Does PPI apply to printing?
The same math becomes DPI/PPI for images: a 3000×2400 px photo printed at 10×8 inches is 300 PPI — photo quality. Printed at 30×24 it drops to 100 PPI and looks soft up close but fine on a wall — distance again.
Is this PPI calculator free?
Yes — free, instant, no sign-up.