How to Calculate Monitor Bandwidth Properly

1. Basic Understanding of Monitors

The main parameters of a monitor include:

• Resolution: The total number of pixels on the screen, usually expressed as the number of horizontal and vertical pixels, such as 1920×1080 (i.e., 1080p).

• Refresh Rate: The number of times the monitor updates its display per second, expressed in Hertz (Hz), such as 60Hz or 144Hz.

• Color Depth: The ability of each pixel to display colors. The higher the color depth, the richer and smoother the colors presented by the monitor, such as 8-bit or 10-bit.

These parameters are crucial for calculating the bandwidth requirements of a monitor.

2. Incorrect Calculation

Let’s calculate the bandwidth needed for a 1080P@60Hz 8-bit monitor. Some might immediately calculate as follows:

The screen has 1920 by 1080 pixels, with each pixel composed of three subpixels (red, green, and blue), refreshed 60 times per second at 8-bit depth. Therefore:

1920 * 1080 * 60 * 8 * 3 = 2.986 Gbit/s

This formula is widely seen online. However, it is incorrect.

3. How Monitors Work

To understand the correct formula, it’s essential to learn how monitors function.

A monitor does not refresh the screen frame-by-frame like a slideshow. Instead, it uses progressive scanning: the display refreshes line-by-line, starting from the top-left corner, moving horizontally to the right, and downwards to the bottom-right corner. Once all lines are refreshed, a full frame is completed.

However, challenges arise here. Electromagnetic interference, Wi-Fi, mobile signals, and high-frequency signals within the computer and monitor circuits can disrupt the transmission, causing misalignment or tearing of the displayed image. To mitigate this, monitors reserve a portion of the pixel area for synchronization and clock alignment, even though these pixels are not part of the visible display. Therefore, this reserved portion must be included in bandwidth calculations.

4. Actual Pixel Count Calculation

The transmitted image comprises three sections:

• Sync Signal Area: Divided into Horizontal Sync (Hsync) and Vertical Sync (Vsync).
• Blanking Area: Divided into Front Blanking and Back Blanking.
• Active Display Area.

Thus, the total transmitted dimensions are:

Htotal = Hsync + Hfront + Hactive + Hback
Vtotal = Vsync + Vfront + Vactive + Vback

The total pixels per frame are:

pixels_per_frame = Htotal * Vtotal

Multiplying this by the refresh rate gives the pixel clock:

pixel_clock = Htotal * Vtotal * Hz

To determine the pixel count of Sync and Blanking areas, refer to the timing standard followed by the monitor. Different standards allocate different pixel areas for clock synchronization and alignment.

Common standards include (download link here):

• CVT Timing Standard
• CVT-RB Timing Standard
• CVT-R2 Timing Standard

Newer interfaces use less bandwidth. Modern DisplayPort interfaces adopt the latest CVT-R2 standard, which provides formulas for calculating Blanking and Sync areas. 

If manually calculating for every resolution seems tedious, VESA provides an Excel sheet (search for "CVT VESA") that automates these calculations. Enter the resolution and refresh rate to obtain the necessary parameters.

For example, calculating Pixel Clock for a 1080p@60Hz monitor:

133.187 MHz * 8 (bits) * 3 (RGB channels) = 3.196 Gbit/s

For HDMI and DisplayPort standards supporting various resolutions and refresh rates, refer to the tables below (or click the links for the full details):

HDMI

DisplayPort

The "DSC" in the tables refers to Display Stream Compression, a technology that provides near-lossless compression for visuals.

The "4:2:0" indicates chroma subsampling, which reduces color resolution while retaining perceptual quality. However, this method is less effective than DSC for maintaining optimal visual quality.