What is PPI? How to Calculate Screen PPI for Displays

What is PPI?

PPI (Pixels Per Inch) means the number of pixels packed into one inch of a screen. It is one of the most important indicators of display sharpness.

In simple terms, higher PPI usually means a clearer and more detailed image, especially when viewing text or UI interfaces.

In industrial display design, we often treat PPI as a practical metric to judge whether a screen is suitable for human-machine interaction (HMI), not just for visual quality.

Why PPI Matters in Real Display Applications

PPI is not just a “spec sheet number”. It directly affects how users interact with devices.

For example:

• Low PPI → UI looks blocky or unclear

• Medium PPI → balanced readability and cost

• High PPI → sharp image but higher cost and processing demand

In our experience at FANNAL, choosing the wrong PPI often leads to real usability problems in industrial equipment, especially in environments like factories, medical devices, or outdoor systems.

That’s why we always evaluate PPI together with viewing distance and product application—not in isolation.

How to Calculate PPI of a Screen

The standard formula is:

PPI = √(W² + H²) ÷ D

Where:

• W = horizontal resolution (pixels)

• H = vertical resolution (pixels)

• D = screen size (inches)

This formula calculates the diagonal pixel density of a display.

Simple Example

Let’s take a common example:

• Resolution: 1920 × 1080

• Screen size: 15.6 inch

Even though the resolution is standard Full HD, the perceived sharpness depends heavily on screen size.

A smaller display with the same resolution will have much higher PPI, and look significantly sharper.

This is why we always say:

Resolution alone does not define display quality. PPI is what users actually feel.

Is Higher PPI Always Better?

Not really.

Higher PPI improves sharpness, but in industrial or embedded systems, it can also introduce unnecessary cost and design complexity.

For example:

• A factory HMI does not need ultra-high PPI

• A handheld medical device may require higher PPI

• Outdoor equipment prioritizes brightness over pixel density

So in real projects, we always balance:

• readability

• cost

• viewing distance

• interface complexity

There is no universal “best PPI”.

Recommended PPI by Application

Based on our project experience in industrial display manufacturing:

• Industrial HMI panels: 100–200 PPI

• Medical devices: 200–350 PPI

• Automotive displays: 150–300 PPI

• Portable smart devices: 250+ PPI

These are not strict rules, but practical engineering ranges we often use when designing TFT LCD solutions.

PPI vs Resolution vs Screen Size

Many people confuse these three:

• Resolution = total number of pixels

• Screen size = physical dimension

• PPI = pixel density per inch

In real display engineering, we never evaluate them separately.

We always combine all three to decide whether a panel is suitable for a product.

How We Work at FANNAL

At FANNAL, we design and manufacture custom TFT LCD and touch display solutions for industrial applications.

We don’t just “sell standard screens”. We help customers build the right display system based on real product requirements.

This includes:

• selecting resolution based on UI design

• optimizing PPI for viewing distance

• matching touch structure (CTP / G+G / bonding)

• Improving outdoor readability with high-brightness solutions

In many cases, the final display we design is not a standard off-the-shelf panel, but a customized combination of size, resolution, and optical structure.

When You Should Contact Us

If you are currently designing a product and unsure about:

• What resolution to choose?

• What PPI is suitable?

• How to balance cost and readability?

• Or how to integrate touch and LCD

Then it usually makes sense to talk to a display manufacturer early.

We can help you avoid over-spec or under-spec design decisions, which often happen in early product development stages.

FAQ

Does viewing distance affect the ideal PPI?

Yes. Displays viewed at close range usually require higher PPI for comfortable readability and sharper UI details.

Why do industrial displays often use lower PPI?

Industrial interfaces prioritize readability and reliability. Large UI elements usually do not require extremely high pixel density.

Can two screens with the same PPI look different?

Yes. Brightness, contrast, panel technology, and optical bonding also affect perceived display quality.

Is a higher PPI always better for touch screens?

Not always. Very high PPI may increase cost and reduce touch usability if UI elements become too small.

Does PPI affect TFT LCD hardware design?

Yes. PPI influences resolution selection, driver IC requirements, and interface bandwidth in display development.