PPI Calculator
Pixels per inch from screen resolution and diagonal size, with dot pitch, physical width and height, and the viewing distance at which single pixels disappear.
The interactive tool loads here when JavaScript runs.
About this toolWhat is the PPI Calculator?
Two screens with the same resolution can look completely different. A 1920 x 1080 panel on a phone is pin sharp; the same pixel count on a 65 inch TV shows visible structure if you sit close. Pixel density, measured in pixels per inch (PPI), is the number that captures the difference. Enter a screen's resolution and diagonal and this calculator gives its PPI, the dot pitch between pixels, its physical width and height, the aspect ratio and the total pixel count.
It also answers the practical question behind most PPI searches: will I see the pixels? Using the common assumption that normal vision resolves detail down to one arcminute, it works out the distance beyond which single pixels blend together, and if you type your own viewing distance it tells you which side of that line you are on. Presets for common monitors, laptops, phones, tablets and TVs fill in typical specs, labelled approximate.
- PPI and pixels per centimetre from resolution and diagonal in inches or cm
- Dot pitch, physical width and height, aspect ratio and total megapixels
- Viewing distance at which pixels blend, using a stated one arcminute acuity
- Verdict and pixels per degree at your own viewing distance
- Approximate presets for monitors, laptops, phones, tablets and TVs, with a comparison table
How to use the PPI Calculator
- Pick a preset or choose Custom and enter the horizontal and vertical resolution in pixels.
- Enter the diagonal size in inches or centimetres.
- Optionally enter how far you sit from the screen.
- Read PPI, pixels per centimetre, dot pitch, physical size, aspect ratio and total pixels.
- Check the "pixels blend beyond" distance, and the verdict for your own viewing distance.
Worked examples
27 inch QHD monitor
Input
2560 x 1440, 27 in, viewed at 28 in
Output
108.8 PPI, dot pitch 0.233 mm, 23.5 x 13.2 in; pixels blend beyond 31.6 in
At a typical 28 in desk distance the pixels are just resolvable, which is why many people step up to a 4K panel at this size (163.2 PPI).
Full HD at two sizes
Input
1920 x 1080 at 24 in and at 15.6 in
Output
91.8 PPI and 141.2 PPI
The laptop panel needs to be viewed from only 24.3 in for pixels to disappear, against 37.5 in for the 24 in monitor.
4K TV
Input
3840 x 2160, 65 in
Output
67.8 PPI; pixels blend beyond 50.7 in
From a normal sofa distance of 2 to 3 m, a 65 in 4K set is well past the point where single pixels can be seen.
Background and insight
A screen's diagonal in pixels follows from Pythagoras: √(width² + height²). Divide that by the diagonal in inches and you have pixels per inch, assuming square pixels, which every modern panel uses. A 27 inch 2560 x 1440 monitor has a 2,937 pixel diagonal, so 2,937 / 27 = 108.8 PPI. Dot pitch, the distance between pixel centres, is 25.4 / PPI in millimetres: 0.233 mm here.
Visual acuity of 20/20 (6/6) corresponds to resolving detail about one arcminute across, one sixtieth of a degree. A pixel of pitch p subtends one arcminute at a distance d = p / tan(1′), or about 3,438 / PPI inches. Beyond that distance a person with 20/20 vision should not resolve individual pixels; this is the idea behind marketing terms such as "Retina". Many people, especially younger viewers, see better than 20/20, so this is a guide rather than a hard limit.
Advertised diagonals are rounded and measure the visible area, so a maker's published PPI may differ by a point or two from the calculated one. A phone sold as 6.1 inches with 2532 x 1170 pixels calculates to 457 PPI from the rounded size; the maker quotes 460 from the exact 6.06 inch diagonal.
Common use cases
Choosing a monitor
Compare sizes and resolutions on pixel density and check that text will look sharp at your desk distance.
TV size and seating
Find how close you can sit to a TV before pixel structure shows.
UI and asset design
Work out physical sizes and device pixel ratios when designing for a specific phone or tablet.
Spec sheet checks
Confirm a quoted PPI and dot pitch, or calculate them for a display with no published figure.
Tips and limitations
- PPI describes the screen; DPI is a print term for ink dots. Image files carry a DPI tag that has no effect on a screen.
- Operating systems scale interfaces on dense screens (125%, 150%, 200%), so a high-PPI monitor shows sharper text rather than smaller text.
- Non-square pixels are rare today, but some older TVs and projectors used them; this calculation assumes square pixels.
- For VR headsets, pixels per degree is a better measure than PPI, because the lenses magnify the panel.
- Use the cm option for screens specified in centimetres; the maths converts with 1 in = 2.54 cm exactly.
Frequently asked questions
How do you calculate PPI?
PPI = √(width² + height²) / diagonal in inches, with width and height in pixels. A 1920 x 1080 screen with a 24 in diagonal has 2,203 pixels on the diagonal, so 2,203 / 24 = 91.8 PPI.
What is a good PPI for a monitor?
At a typical desk distance of 50 to 70 cm, around 100 to 110 PPI looks acceptable at 100% scaling, and 140 PPI or more with 150% to 200% scaling gives noticeably sharper text. A 27 in 4K monitor is 163 PPI.
At what distance can you not see pixels?
Assuming 20/20 vision resolves one arcminute, pixels blend beyond about 3,438 / PPI inches. For a 108.8 PPI monitor that is 31.6 in; for a 326 PPI phone it is about 10.5 in.
What is the difference between PPI and DPI?
PPI counts pixels per inch on a screen or in an image. DPI counts ink dots per inch from a printer, and printers use several dots to make each image pixel. The terms are often mixed up, and DPI is commonly used to mean PPI when sizing prints.
What is dot pitch?
Dot pitch is the distance between the centres of neighbouring pixels, usually in millimetres. It is 25.4 / PPI, so a 108.8 PPI monitor has a 0.233 mm dot pitch. Smaller is sharper.
Is higher PPI always better?
Only up to the point where you can no longer see pixels at your viewing distance. Beyond that, more PPI costs more graphics power and battery for little visible gain, although very fine text and lines still benefit slightly.
Is there an in-depth guide to the PPI Calculator?
Yes. “Pixel Density Explained: PPI, Dot Pitch and the Retina Threshold” covers the background, how it works, common pitfalls and worked examples. Read the full guide.
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