DPI Calculator

1. Enter the screen width and height in pixels, its resolution.
2. Enter the diagonal size in inches.
3. Read the pixel density, the diagonal in pixels and the dot pitch, all updating live.

Each output describes the display:

PPI, pixels per inch, measures how densely a screen packs its pixels. A higher PPI means smaller, more tightly spaced pixels and a sharper image, because your eye cannot pick out the individual dots. The term DPI, dots per inch, comes from printing but is widely used to mean the same thing for screens.

Two screens with the same resolution can have very different densities if their sizes differ. A 1080p image looks razor sharp on a small phone but softer on a large television, because the same pixels are spread over more inches. Density, not resolution alone, decides sharpness.

It finds the diagonal length in pixels with Pythagoras, then divides by the diagonal size in inches.

The diagonal in pixels is sqrt(w^2 + h^2), and dividing it by the physical diagonal gives the density PPI = sqrt(w^2 + h^2) / d. The dot pitch, the spacing between pixels, is then 25.4 / PPI millimetres, since there are 25.4 millimetres in an inch.

1. Square the width and height in pixels and add them.
2. Take the square root for the diagonal in pixels.
3. Divide by the diagonal in inches for the pixels per inch.

Because it uses the diagonal, the result does not depend on the aspect ratio being any particular shape.

A 1920 by 1080 laptop screen measuring 15.6 inches has a diagonal of sqrt(1920^2 + 1080^2) = 2203 pixels. Dividing by 15.6 gives 2203 / 15.6 = 141 pixels per inch, with a dot pitch of about 0.18 millimetres.

Shrink the same 1080p resolution onto a 6.1-inch phone and the density soars past 400 PPI, far sharper, which is why phone text looks so crisp. Stretch it onto a 32-inch monitor and it drops below 70 PPI, where pixels become visible up close.

A 27-inch 1440p monitor lands around 109 PPI, a comfortable middle ground for desktop work at arm's length.

These rough bands help you judge whether a screen will look sharp.

Viewing distance matters too: a TV seen from across a room needs far less density than a phone held close. To compare screen shapes, the aspect ratio calculator is a useful partner.

Only resolution and size set the density, but a few points are worth knowing.

Resolution

More pixels across the same screen raise the density and the sharpness directly.

Screen Size

Spreading the same resolution over a larger diagonal lowers the density, softening the image.

Viewing Distance

Density needed for a sharp look falls with distance, so a distant TV can have far fewer pixels per inch.

Sub-pixel Layout

Some panels arrange coloured sub-pixels unusually, so perceived sharpness can differ slightly from the raw PPI.

Comparing Screens

Put two displays on the same footing by their pixels per inch rather than resolution alone.

Choosing a Monitor

Check whether a size and resolution will look sharp at your usual viewing distance before buying.

Design and Development

Know a target screen density when preparing images or setting scaling for an interface.

1. Judging Sharpness by Resolution Alone

The same resolution looks very different on a phone and a TV. Density is what matters.

2. Using the Width Instead of the Diagonal

Screen size is the diagonal measurement, not the width, so use the diagonal in inches.

3. Confusing DPI with Resolution

Resolution is the total pixel count; DPI or PPI is how tightly those pixels are packed.

4. Ignoring Viewing Distance

A high density adds little benefit on a screen viewed from far away.

5. Mixing Inches and Centimetres

The diagonal must be in inches for pixels per inch; convert first if it is in centimetres.

The math is exact for the resolution and diagonal you enter, using the standard geometry of a screen.

Find the diagonal in pixels with the square root of width squared plus height squared, then divide by the diagonal in inches. This calculator does both steps.

PPI, pixels per inch, is the correct term for screens. DPI, dots per inch, comes from printing but is often used loosely to mean the same thing for displays.

Around 100 to 150 PPI is comfortable for a desktop monitor at arm's length. Laptops often sit at 150 or more, and phones exceed 300.

Sharper, yes, but with diminishing returns beyond what your eye can resolve at your viewing distance. A distant TV needs far less density than a phone.

Resolution is the total number of pixels, such as 1920 by 1080. PPI is how tightly those pixels are packed, which depends on the screen size too.

Dot pitch is the distance between neighbouring pixels, in millimetres. It is 25.4 divided by the PPI, so a higher density means a smaller pitch.

No. Because PPI uses the diagonal, it does not depend on the screen being any particular shape, only on the resolution and the diagonal size.

It is a marketing term for a density high enough that a typical viewer cannot see individual pixels at normal distance, often around 300 PPI or more on phones.

No. The calculation runs in your browser, and nothing you enter is sent anywhere unless you Save a result, which stays on this device only.

• Dots per inch (Wikipedia).
• Pixel density (Wikipedia).
• Unit of length (Wikipedia).