π₯οΈ PPI Calculator
Find screen pixel density, megapixels, aspect ratio, and print sizes.
Pixels Per Inch
How to Use This PPI Calculator
Enter the horizontal and vertical pixel counts of your screen or image, plus the diagonal screen size in inches for a display. The calculator returns the pixel density, total megapixels, simplified aspect ratio, and the physical print sizes at common DPI values.
Enter the resolution, for example 1920 horizontal and 1080 vertical pixels.
Enter the diagonal screen size in inches. Find it on the product box or the manufacturer spec page. For a photo file with no screen size, leave it blank and you still get megapixels and print sizes.
Read the results: PPI, megapixels, aspect ratio, and print dimensions at 300, 150, and 72 DPI.
Use the print sizes to decide whether an image is big enough for a poster or only for screen use.
The PPI Formula
PPI is found with the Pythagorean theorem: the pixel diagonal of the screen divided by its physical diagonal in inches. Megapixels are simply the total pixel count divided by one million. Aspect ratio comes from reducing the resolution by its greatest common divisor, so 1920x1080 becomes 16:9. Print size divides each pixel dimension by the target DPI: 300 for photo quality, 150 for large prints viewed at a distance, and 72 for reference to screen resolution.
Worked Example
A 1920x1080 monitor with a 24 inch diagonal. Diagonal pixels = sqrt(1920^2 + 1080^2) = sqrt(4,852,800) = 2202.9 pixels. PPI = 2202.9 / 24 = 91.8 PPI. Megapixels = (1920 x 1080) / 1,000,000 = 2.07 MP. Aspect ratio = 16:9. At 300 DPI the image prints at 1920/300 = 6.4 inches wide and 1080/300 = 3.6 inches tall, so a 6.4 x 3.6 inch photo at full quality. At 150 DPI the same image covers 12.8 x 7.2 inches.
What the Numbers Mean in Practice
PPI only tells part of the story, because viewing distance matters. A 55 inch 4K TV has about 80 PPI, but from a couch ten feet away it looks perfectly sharp. A phone at 400 PPI looks stunning in your hand but would be wasted on a billboard. For photography, check megapixels and print size rather than PPI: a 24 MP camera gives a 20 x 13.3 inch print at 300 DPI, plenty for framing. For monitors, 90 to 110 PPI is the classic desktop range, 140 to 160 PPI is the sharper modern sweet spot, and above 200 PPI you are in retina territory where individual pixels are invisible at normal distance.
Frequently Asked Questions
What is PPI?
PPI stands for pixels per inch: how many display pixels fit in one linear inch of screen. A higher PPI means a sharper image with less visible pixelation. Smartphones often exceed 400 PPI, desktop monitors usually sit between 90 and 160 PPI, and large TVs can look fine at under 60 PPI because you sit farther away.
What is the difference between PPI and DPI?
PPI describes a screen: pixels per inch of display. DPI describes a printer: dots of ink per inch of paper. They are related but not the same thing. When you print a photo, the image pixels are mapped to printer dots, so a 300 PPI source file printed at 300 DPI gives a true 1:1 result.
What is a good PPI for a monitor?
It depends on viewing distance. For a desktop monitor viewed at arm length, 90 to 110 PPI is standard, 140 to 160 PPI looks noticeably sharper, and above 200 PPI (like 4K at 27 inches) text looks near-print quality. Laptop screens often reach 150 to 250 PPI.
How is aspect ratio calculated from resolution?
Divide both the width and height by their greatest common divisor. For example, 1920x1080 reduces to 16:9, and 2560x1440 also reduces to 16:9. This calculator does the simplification for you automatically.
What print size will my photo give?
Divide the pixel dimensions by the print DPI. A 1920x1080 image at 300 DPI prints at 6.4 x 3.6 inches. For high quality photo prints use 300 DPI, for large posters viewed at a distance 150 DPI is often fine, and 72 DPI is screen resolution, not a print target.