This PPI calculator (pixels per inch calculator) finds the resolution of your display basing on its dimensions and the pixel count. Read on to learn what is the definition of pixel density, how to calculate PPI and how to categorize resolution basing on PPI. Make sure to take a look at our px to em calculator, too!
What is PPI
PPI stands for pixels per inch - a measurement of pixel density (resolution) of a screen such as a computer display or a camera. Essentially, this value tells you how many pixels you can fit along a one inch side of a display.
Our pixel density calculator assumes square pixels, so that the vertical and horizontal PPI are the same.
How to calculate PPI
You can calculate PPI in multiple ways. The most common one is to calculate it from the diagonal screen size (in inches or cm) and the amount of pixels along the vertical and horizontal edge of the display.
First, you need to calculate the number of pixels that fit on the diagonal:
dₒ = √(w² + h²)
- w is the number of pixels along the horizontal, and
- h is the number of pixels along the vertical.
Then, you can calculate the PPI as the ratio between the number of pixels along the diagonal and the diagonal screen size:
PPI = dₒ/dᵢ
where dᵢ is the diagonal screen size in inches.
You probably noticed that you can also enter the width and height of the display into the PPI calculator. You can use these values instead of the diagonal size of the screen. Remember, though, that the aspect ratio must be the same both for the size expressed in inches and pixels.
Our pixel density calculator also finds the total number of pixels on the display, expressed in megapixels (millions of pixels, symbol: Mpx). This value is found as the product of the vertical and horizontal amount of pixels.
The last number that you can find with our calculator is the dot pitch - the distance between two pixels' centres. It is found as the inverse of PPI.
Using the pixels per inch calculator: an example
Let's assume you want to calculate the PPI of your smartphone.
- Check what is the diagonal size of your smartphone. Let's say it is equal to 5 inches.
- Write down the vertical and horizontal pixel count. Let's assume they are equal 640 and 480 pixels respectively.
- Calculate the amount of pixels along the diagonal:
dₒ = √(w² + h²) = √(480² + 640²) = √640,000 = 800
- Calculate the PPI according to the formula written above:
PPI = dₒ/dᵢ = 800/5 = 160
- The total count of pixels is found as the product of w and h:
w * h = 480 * 640 = 307,200 = 0.307 Mpx
- Calculate the dot pitch as the reciprocal of PPI:
dot pitch = 1/160 in = 0.00625 in = 0.1588 mm
Pixel density categories
The list below presents the categories of pixel density - from the lowest to highest quality.
- LDPI: Low density, 120 PPI
- MDPI: Medium density, 120-160 PPI
- TVDPI: Medium High density, 160-213 PPI
- HDPI or HiDPI: High density, 213-240 PPI
- XHDPI: eXtra High density, 240-320 PPI
- XXHDPI: eXtra eXtra High density, 320-480 PPI
- XXXHDPI: eXtra eXtra eXtra High density, 480-640 PPI