If you’re looking at a 3.4 inch round TFT LCD 800x800, the key physical dimensions you need to know are: the display area (active area) is approximately 86.4 mm in diameter, which translates to a radius of about 43.2 mm. The module itself, including the bezel and FPC (flexible printed circuit) connector, typically measures around 90.0 mm in outer diameter and 1.0 mm to 1.5 mm in thickness, depending on the backlight and touch panel options. The 3.4-inch diagonal measurement refers to the circle’s diameter, not a square or rectangle, so the active area is a circle with a diameter of 3.4 inches, which equals 86.36 mm (since 1 inch = 25.4 mm, so 3.4 × 25.4 = 86.36 mm). Manufacturers often round this to 86.4 mm in datasheets. The 800x800 resolution means the pixel density is about 235 PPI (pixels per inch), calculated as 800 pixels / 3.4 inches = 235.3 PPI, which gives sharp details for a round display. For exact mechanical specs, always check the specific product datasheet, but the 3.4 inch round tft lcd 800x800 from DisplayModule, for example, shows an active area diameter of 86.40 mm and a module outline diameter of 89.60 mm, with a thickness of 1.2 mm (excluding FPC and touch panel).
Let’s break down the numbers so you can visualize it. The display is a perfect circle, so the diagonal measurement is the same as the diameter. The 3.4-inch size is a standard for round TFTs, often used in smartwatches, automotive clusters, and IoT devices. The 800x800 resolution gives a 1:1 aspect ratio, which is rare for rectangular screens but common for round ones—it ensures the image fills the circle without distortion. The pixel pitch is about 0.108 mm (calculated as 86.4 mm / 800 pixels = 0.108 mm per pixel), which means each pixel is 108 micrometers wide—small enough to make text and icons crisp. The active area is a circle with an area of roughly 5860 square millimeters (π × (43.2 mm)^2 ≈ 5860 mm²), so you get a decent viewing surface for a compact device.
Now, let’s talk about the physical footprint. The module’s outer diameter is usually larger than the active area because of the bezel. For the 3.4 inch round TFT LCD 800x800, the bezel width is typically 1.5 mm to 2.0 mm, so the outer diameter ranges from 89.0 mm to 90.0 mm. The thickness varies based on whether you get a standard version (just the LCD with backlight) or an integrated touch panel. A standard version is around 1.0 mm to 1.2 mm thick, while a version with a capacitive touch panel adds about 0.5 mm to 1.0 mm, bringing it to 1.5 mm to 2.2 mm. The FPC connector is usually 12 mm to 15 mm long and 8 mm to 10 mm wide, with a pitch of 0.5 mm or 0.3 mm for MIPI interfaces. The connector itself is typically a 40-pin or 50-pin FPC, depending on the driver IC and interface (like MIPI DSI with 4 lanes).
For a deeper dive, consider the mechanical tolerances. Datasheets for round TFTs often specify a tolerance of ±0.2 mm for the active area diameter and ±0.3 mm for the module outline. So, if the datasheet says 86.40 mm active area, the actual part could be between 86.20 mm and 86.60 mm. Similarly, the module outline might be 89.60 mm ±0.3 mm, meaning it could be 89.30 mm to 89.90 mm. This matters if you’re designing a housing or bezel—you need to account for these tolerances to avoid interference. The thickness tolerance is usually ±0.1 mm for the LCD glass and backlight stack, but the FPC thickness can vary by ±0.05 mm.
Let’s put this in a table for clarity:
| Parameter | Typical Value | Unit | Notes |
|---|---|---|---|
| Diagonal (Diameter) | 3.4 | inches | Standard measurement for round displays |
| Active Area Diameter | 86.4 | mm | Calculated as 3.4 × 25.4; tolerance ±0.2 mm |
| Active Area Radius | 43.2 | mm | Half of diameter |
| Active Area (Circle) | 5860 | mm² | π × (43.2)^2 |
| Module Outer Diameter | 89.6 | mm | Includes bezel; tolerance ±0.3 mm |
| Module Thickness | 1.2 | mm | Without touch panel; ±0.1 mm |
| Pixel Pitch | 0.108 | mm | 86.4 mm / 800 pixels |
| Pixel Density | 235 | PPI | 800 pixels / 3.4 inches |
| Resolution | 800 × 800 | pixels | Square grid within circle |
| FPC Length | 12–15 | mm | Depends on connector type |
| FPC Width | 8–10 | mm | For 40–50 pin connectors |
| FPC Pitch | 0.5 or 0.3 | mm | MIPI interface common |
This table gives you a quick reference, but let’s expand on the real-world implications. The 3.4-inch size is a sweet spot for wearable devices—it’s large enough to show a watch face with complications (like date, step count, heart rate) but small enough to fit on a wrist. The 800x800 resolution means you can display detailed graphics, like a map or a photo, without pixelation. The 235 PPI is comparable to a smartphone’s retina display (which is around 300 PPI), so text is sharp. However, because it’s a round display, the effective pixel count is lower than a square display of the same diagonal—since the circle uses only about 78.5% of the 800x800 grid (the area of a circle inscribed in a square is π/4 ≈ 0.785). So, the actual number of lit pixels is about 502,000 (800 × 800 × 0.785), which is still high for a 3.4-inch screen.
From an electrical perspective, the display uses a MIPI DSI interface with 4 lanes, which is common for round TFTs. The driver IC (like the ILI9488 or ST7701S) supports the 800x800 resolution and handles the round shape by mapping the square pixel grid to the circular active area. The backlight is typically a white LED with a forward voltage of 3.0 V to 3.3 V and a current of 20 mA to 30 mA, giving a brightness of 300 cd/m² to 500 cd/m². The power consumption is around 0.5 W to 1.0 W, depending on brightness and whether the touch panel is active. The FPC connector has a 0.5 mm pitch for the MIPI signals, which requires careful routing on your PCB—trace lengths should be matched to avoid signal skew.
When you’re integrating this display into a product, you need to consider the mounting method. The module has a metal or plastic frame that allows for screw mounting or adhesive bonding. The typical mounting hole diameter is 2.0 mm to 2.5 mm, with a pitch of 80 mm to 85 mm between holes (depending on the frame design). The weight is around 10 grams to 15 grams, including the backlight and FPC, so it’s lightweight for portable devices. The operating temperature range is usually -20°C to +70°C, with a storage range of -30°C to +80°C, which covers most consumer and industrial applications.
Let’s compare the 3.4-inch round display to other common sizes. A 1.28-inch round TFT (like those in smartwatches) has a diameter of 32.5 mm and a resolution of 240×240, with a pixel density of 186 PPI. A 4.0-inch round TFT has a diameter of 101.6 mm and a resolution of 480×480, giving 120 PPI. So, the 3.4-inch 800×800 sits in the middle—larger than a typical smartwatch but smaller than a dashboard display, with a higher resolution than most round screens. This makes it ideal for applications where you need both size and detail, like a smart home hub, a rearview mirror display, or a medical device interface.
For mechanical design, the viewing angle is another factor. Round TFTs often use IPS (In-Plane Switching) technology, which gives wide viewing angles of 80° to 85° in all directions (left, right, up, down). The contrast ratio is typically 800:1 to 1000:1, and the response time is 25 ms to 35 ms (rise + fall). The color gamut is 70% to 80% NTSC, which is good for most applications but not as high as OLEDs. The backlight is edge-lit, with LEDs arranged along the bottom edge of the module, so the brightness is uniform across the circle. The driver IC supports 16.7 million colors (24-bit RGB), so you can display smooth gradients and photos.
One practical detail: the 3.4-inch round TFT LCD 800x800 uses a circular polarizer, which means the display has a specific orientation for optimal viewing. If you rotate the module, the polarization angle changes, which can affect visibility when used with polarized sunglasses. The datasheet usually specifies the polarizer angle (e.g., 0° or 45°), so you need to align it with your product’s design. The glass thickness is 0.5 mm to 0.7 mm for the TFT glass, plus 0.5 mm for the backlight diffuser, giving a total glass stack of 1.0 mm to 1.2 mm. The touch panel (if used) adds another 0.5 mm to 1.0 mm of glass or plastic, with an ITO (Indium Tin Oxide) coating for capacitive sensing.
Now, let’s talk about the FPC in more detail. The FPC is typically 0.2 mm thick and has a stiffener (a piece of polyimide or metal) at the connector end to make it rigid for insertion. The connector is a ZIF (Zero Insertion Force) type, with a locking mechanism to hold the cable. The pin count is usually 40 for a 4-lane MIPI interface, but some modules use 50 pins to include additional signals like a touch controller I2C bus or a backlight PWM pin. The FPC length is customizable, but standard lengths are 12 mm, 15 mm, or 20 mm. If you need a longer cable, you can order a custom FPC, but the standard ones are fine for most designs.
For the backlight, the LEDs are typically 6 to 8 in series, with a total forward voltage of 18 V to 24 V (since each LED is 3.0 V to 3.3 V). The current is 20 mA per LED, so the total backlight power is 0.36 W to 0.48 W. The brightness is adjustable via PWM, with a frequency of 100 Hz to 1 kHz. The backlight lifetime is 30,000 hours to 50,000 hours, which is typical for consumer displays. If you need a higher brightness for outdoor use, you can opt for a version with a brighter backlight (up to 800 cd/m²), but that increases power consumption to 1.0 W to 1.5 W.
From a software perspective, the display uses a MIPI DSI interface, which requires a compatible controller (like a Raspberry Pi, STM32, or ESP32) with a MIPI DSI port. The driver IC initializes the display via SPI or I2C commands, and then the pixel data is sent over the MIPI lanes. The round shape is handled by the driver IC, which accepts a square frame buffer and masks the corners to create a circle. The frame rate is 60 Hz, which is smooth for animations and video. The memory buffer is 800 × 800 × 24 bits = 1.92 MB, so you need a microcontroller with enough RAM or an external frame buffer.
For reliability, the display is tested for shock and vibration, with a typical rating of 100 G for 6 ms (half-sine pulse) and 10 Hz to 55 Hz vibration at 1.5 mm amplitude. The humidity range is 10% to 90% RH (non-condensing). The RoHS and REACH compliance is standard for most modules. The electrostatic discharge (ESD) protection is 4 kV for contact discharge and 8 kV for air discharge, per IEC 61000-4-2. These specs make it suitable for industrial and automotive environments, as long as you add a cover glass or lens for protection.
Finally, let’s talk about cost and availability. The 3.4 inch round TFT LCD 800x800 is a niche product, so it’s not as cheap as rectangular displays. A typical unit costs $15 to $30 in small quantities, with volume discounts for 100+ pieces. The lead time is 4 to 6 weeks for standard orders, but some suppliers stock them for immediate delivery. The module is available with or without a touch panel, and you can choose between a standard FPC or a custom one. The connector type is usually a 0.5 mm pitch ZIF, but some modules use a 0.3 mm pitch for thinner cables. Always check the datasheet for the exact pinout and mechanical drawing before ordering.