PPI / DPI & Print Size Calculator
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
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Calculator
Screen density: Standard
Typical desktop resolution (72–119 PPI). Pixels are visible up close but fine at arm's length.
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.
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.
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.
Sources
Reviewed by the YouCalc Team · Last reviewed
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