Calculate screen pixel density (PPI), print dimensions from pixel counts, or pixels needed for a print target — and understand the PPI vs DPI difference.
PPI
91.8
Calculator
Pixel density
91.8 PPI
Print quality
Draft
Print quality: Draft
Suitable for large-format banners viewed from a distance.
PPI vs DPI — what's the difference?
PPI (pixels per inch) is a screen metric. It tells you how densely the pixels are packed on a display. Higher PPI means sharper text and images. You calculate it from the screen resolution (width × height in pixels) and the physical diagonal size in inches using the Pythagorean theorem: PPI = √(width² + height²) / diagonal.
DPI (dots per inch) is a printer metric. It measures how many ink dots a printer lays down per inch. For print, you need enough source pixels — a 10 × 8 inch photo at 300 DPI requires 3,000 × 2,400 pixels. Below 150 DPI prints look blurry; 300 DPI is the standard for photo-quality prints.
The three modes above cover the most common conversions: finding your screen's PPI, working out how large an image will print at a given DPI, and calculating how many pixels you need to hit a target print size at a given quality.
What PPI do I need for a retina/HiDPI screen?
Apple's 'Retina' threshold is roughly 220 PPI for devices held at arm's length (phones are typically 300–460 PPI). For monitors at desk distance, 110–160 PPI is generally considered sharp enough for most users.
What DPI should I use for printing photos?
300 DPI is the standard for photo-lab printing. 240 DPI is the minimum for photos you'll look at closely. Posters viewed from a metre or more can look fine at 150 DPI or even lower.
Is PPI the same as resolution?
No. Resolution is the total pixel count (e.g. 1920 × 1080). PPI is the density — how those pixels are spread across the physical screen size. A 4K panel on a 55-inch TV has lower PPI than the same 4K panel on a 27-inch monitor.
Results are estimates. Verify with a professional for important decisions.
About this calculator
This calculator helps you understand pixel density and print sizing. Find the PPI (pixels per inch) of any screen from its resolution and diagonal size, work out how large a photo will print at a given DPI, or calculate how many pixels you need to fill a target print size at photo-lab quality.
How to read your results
Switch between the three modes using the tabs. In Screen PPI mode the headline result is the pixel density of your display — higher means a sharper image at normal viewing distance. In Print Size mode the result shows the physical dimensions your image will produce at the chosen DPI, together with a quality rating (draft, good, or photo). In Pixels Needed mode the result tells you the minimum pixel count required to print at a given size and quality level.
Worked example
A 1920 × 1080 pixel image printed at 300 DPI. Enter width 1920, height 1080, and DPI 300 in Print Size mode.
The image prints at 6.40 × 3.60 inches (16.26 × 9.14 cm) and qualifies as photo quality. At 300 DPI, every inch contains 300 pixels — the standard for photo-lab output.
Frequently asked questions
What is PPI and how is it different from DPI?
PPI (pixels per inch) describes screen pixel density — how many pixels are packed into each inch of your display. DPI (dots per inch) describes printer dot density — how many ink dots a printer lays down per inch. Both measure sharpness, but PPI applies to screens and DPI applies to printed output. A 300-DPI print from a 72-PPI screen image will look soft because the original does not contain enough pixels.
Why is 300 DPI the standard for photo printing?
The human eye resolves detail up to roughly 300 dots per inch at normal reading distance (about 30 cm). Photo labs and professional printers use 300 DPI as the baseline because it captures all the detail the eye can distinguish without wasting file size. Enlargements viewed from farther away can look fine at 150–200 DPI.
My screen is 72 PPI — does that mean prints from it will be blurry?
Screen PPI and print DPI are independent settings. When you export an image from photo software, you choose the pixel dimensions and the output DPI separately. A photo stored as 4500 × 3000 pixels will print sharply at 300 DPI regardless of the PPI of the screen it was edited on. It is the pixel count in the file that limits print quality, not the display PPI.
How does the PPI formula work?
The calculator uses the Pythagorean theorem: the diagonal pixel count is the square root of (width² + height²), and PPI is that number divided by the physical diagonal in inches. For a 1920 × 1080 display on a 27-inch screen: √(1920² + 1080²) ÷ 27 ≈ 81.6 PPI.
What print quality ratings mean?
Below 150 DPI is draft quality — acceptable only for large-format banners viewed from a distance. 150–239 DPI is good quality, suitable for everyday office or home printing. 240 DPI and above is photo quality, matching or exceeding what the human eye can resolve at close range. 300 DPI is the industry standard for photo-lab output.
How it's calculated
Screen PPI is computed with the Pythagorean theorem: PPI = √(widthPx² + heightPx²) ÷ diagonalInches. This gives the pixel count along the diagonal, which is then divided by the physical diagonal length to get pixels per inch. Print size in inches is simply pixels ÷ DPI for each axis; centimetres are obtained by multiplying inches by 2.54. Pixels needed for a target print size are calculated as round(inches × DPI). PPI is a screen property; DPI is a printer property — they describe the same concept (density) in different output media. The 300-DPI rule of thumb for photo printing comes from the resolving limit of the human eye at a normal viewing distance of about 30 cm. Quality thresholds used here: below 150 DPI is draft, 150–239 DPI is good, 240 DPI and above is photo quality.
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