There's a size range that keeps coming up in our order history: 3.5" to 7". It's not a coincidence.

This is the range where displays start doing real work — big enough to show a proper UI with multiple data fields, touch targets, and graphical elements, but still compact enough to fit into a panel cutout without dominating the enclosure. Whether you're building a PLC interface, a test instrument, a home automation panel, or a Raspberry Pi-based device, there's a strong chance the right display for your project lives somewhere in this range.

Here's a closer look at what we offer in 3.5" to 7", what each size is actually used for, and what to consider when specifying one.

3.5 inch: the workhorse of embedded HMI

The 3.5" module is our most versatile product in this range. It's the standard size for Raspberry Pi display add-ons, Arduino Mega shields, and small handheld industrial devices.

Typical specs:

• Resolution: 320×480 (ILI9488 driver) or 480×320 landscape
• Interface: SPI or 8-bit parallel (8080)
• Touch: optional resistive (XPT2046) or capacitive (GT911)
• Viewing angle: IPS panel available for wide-angle applications

Where it gets used: Machine operators who need to see 4–6 data fields at once without squinting. Portable test equipment where the display needs to be readable in varying lighting conditions. Custom POS terminals where a touchscreen is needed but a 7" panel would be overkill.

The 3.5" is also popular in the maker community for Raspberry Pi 3/4 projects — it fits the Pi's GPIO header directly and sits neatly on the board without requiring a separate mounting solution.

4.0 inch: when 3.5" is just slightly too small

The 4.0" module doesn't get as much attention as the 3.5" or 5.0", but for some applications it's exactly right.

Typical specs:

• Resolution: 480×800 (ST7796 driver)
• Interface: SPI or RGB
• Touch: capacitive multi-touch available
• Brightness: up to 500 cd/m² for sunlight-readable variants

Where it gets used: In-vehicle displays where the mounting space is fixed. Portable medical devices where the form factor is dictated by regulatory approval. Industrial handhelds where the operator is wearing gloves (resistive touch recommended in this case).

The 480×800 resolution at 4.0" gives roughly 233 PPI — noticeably sharper than the same resolution on a 3.5" panel, and well above the threshold where individual pixels become visible in normal use.

5.0 inch: the entry point for serious panel UIs

At 5.0", you have enough screen real estate to build a genuine multi-screen application — navigation menus, data charts, form inputs, status dashboards. This is where most industrial HMI work happens.

Typical specs:

• Resolution: 800×480 (landscape) with RGB interface
• Touch: projected capacitive (PCAP), 5-point multi-touch
• Brightness: 400–800 cd/m² depending on variant
• Operating temperature: -20°C to +70°C (industrial grade available)

Where it gets used: Factory floor terminals. Smart home control panels. Agricultural equipment dashboards. Any application where the operator needs to interact with the display while doing something else with at least one hand — the larger touch targets on a 5" panel make a real difference in usability.

If you're running an embedded Linux system (iMX6, RK3288, or similar), the 5.0" RGB panel is a natural pairing — the parallel RGB interface connects directly to the SoC's display controller without a bridge IC.

7.0 inch: full-panel HMI, still field-deployable

The 7.0" is the upper end of what most people consider "portable." It's used in applications where the display is the primary interface for a system — not a status readout, but a full control surface.

Typical specs:

• Resolution: 1024×600 (standard) or 800×480
• Interface: LVDS or MIPI DSI (for high-resolution variants), RGB for 800×480
• Touch: PCAP, 10-point multi-touch
• Brightness: 500–1000 cd/m² for outdoor-readable variants
• Panel type: IPS standard (160° viewing angle)

Where it gets used: Marine chartplotters and navigation systems. Industrial automation panels mounted in cabinet doors. Medical imaging carts where the display is used by clinicians at varying angles. Kiosk applications where the device will be handled by many different users.

The 7.0" MIPI DSI panel at 1024×600 gives a crisp, detailed display that holds up well to direct sunlight with a high-brightness backlight option. If your deployment environment includes outdoor or high-ambient-light conditions, specify the 700+ nit variant.

What to specify when you contact us

When you reach out about a display in this size range, the questions we'll ask are:

1. Interface requirement — Are you using an SoC with a native RGB/LVDS/MIPI output, or do you need an MCU-friendly SPI/parallel interface?
2. Touch type — Resistive (stylus, gloves, outdoor) or capacitive (smooth multi-touch, indoor)?
3. Brightness requirement — Standard (300–400 nit) for indoor, high-brightness (600–1000 nit) for outdoor or high-ambient environments.
4. Operating temperature range — Consumer grade (0°C to +50°C) or industrial grade (-20°C to +70°C)?
5. Volume — Sample quantities, small batch, or production volumes? This affects whether a standard module or a semi-custom solution makes more sense.

The more detail you give us upfront, the faster we can point you to the right module — or tell you if a custom solution would serve you better.

Why engineers and buyers choose POLCD for this range

We've been manufacturing TFT LCD modules since the early days of embedded touchscreen interfaces. The 3.5"–7" range is where the majority of our industrial and B2B orders land, and it's the range we know best.

Ready to spec your display? Browse our 3.5"–7" TFT LCD module range, or send us your project requirements for a direct recommendation.

[View 3.5–7 Inch TFT LCD Modules →] POLCD Digital Products
[Contact POLCD Technical Sales →] Billie@polcd-digital.com