Open the PPI / DPI Calculator
Calculate a screen's real pixels-per-inch (PPI) from its diagonal size and resolution, or work out the exact pixel resolution needed to print an image at.
- Free to use
- No signup
- Nothing to install
- Runs in your browser
Illustration. Open the tool for the real thing.
See it in action
Sample input: Diagonal screen size (inches) = 27; Horizontal resolution (px) = 2560; Vertical resolution (px) = 1440
What is the PPI / DPI Calculator?
Enter a screen's diagonal size and its horizontal and vertical resolution, and this tool calculates its real pixel density (PPI, pixels per inch) using the actual Pythagorean geometry involved: the diagonal resolution in pixels is found from the horizontal and vertical pixel counts, then divided by the physical diagonal size in inches — the same real math manufacturers use to publish a display's PPI spec.
Switch to print mode for the reverse, more common everyday question: given a physical print size (like 4x6 inches) and a target print quality in DPI (dots per inch — 300 DPI is the standard for sharp photo prints), this tool calculates the exact pixel dimensions your image file needs to be, so you know before you order a print or design a template whether your photo has enough resolution.
3 steps to your result
Open the tool and follow along. Nothing to install.
What you get
Uses the actual Pythagorean calculation from horizontal/vertical resolution, not an approximation.
Find a display's true pixel density from its size and resolution.
Calculate the exact pixel dimensions needed for a target print size and DPI.
Real math, not a rounded lookup table.
AZRS tools are free to open and use.
It opens in your browser, so there is nothing to download.
Used for
Pick one to see how it fits.
Anyone comparing monitor or phone screen sharpness
Get the real PPI number instead of relying on marketing claims.
Try it freePhotographers and print buyers
Confirm an image has enough resolution before ordering a physical print.
Try it freeDesigners setting up a print template
Work out the exact pixel canvas size needed for a target print size and DPI.
Try it freeHow it compares
A plain look at this tool next to the usual alternative.
| This utility | Desktop software | |
|---|---|---|
| Install | Nothing to install | Usually an app or program to install |
| Account | No signup | Depends on the product |
| Cost | Free to use | Free or paid, depends on the product |
| Where it runs | In your browser tab | On your computer |
Questions people ask
What is PPI?
Pixels per inch — a measure of how densely packed a screen's (or image's) pixels are, calculated from the diagonal pixel count divided by the physical diagonal size in inches.
What DPI do I need for printing photos?
300 DPI is the standard for sharp, professional-quality photo prints; 150 DPI is acceptable for large posters viewed from further away.
Is PPI the same as DPI?
Technically PPI describes pixel density on a screen or in a digital image, while DPI describes dots of ink from a printer or a scanner's sampling rate — in casual use the two terms are very often used interchangeably.
How is PPI calculated?
The diagonal pixel count is found using the Pythagorean theorem from the horizontal and vertical resolution, then divided by the display's physical diagonal size in inches.
What resolution do I need for a 4x6 inch print at 300 DPI?
1200 x 1800 pixels — multiply each physical dimension in inches by the target DPI.
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