CAN bus: Baud Rate and its calculation

CAN (Controller Area Network) systems, the terms baud rate and bit rate are often used interchangeably, but they refer to different aspects of communication.


Baud Rate: Baud rate refers to the number of signal changes (transitions between voltage levels) that occur on the bus each second. It’s a measure of how fast the physical layer is operating. In most CAN tools and settings, this is what’s labelled as the "baud rate."


Bit Rate: Bit rate is the number of bits transmitted on the CAN bus each second. This includes data, and all parts of the CAN frame, such as message identifiers, control fields, and error-checking bits. Each bit is divided into timing segments defining sampling and synchronisation. These segments affect timing accuracy, not the overall bit rate.


Although the terms are often used loosely, it’s important to understand their roles. Especially when configuring CAN timing or diagnosing communication problems.

Baud rate defines how quickly bits are transmitted on the bus, measured in bits per second (bps). This directly affects how fast messages move between nodes.

The CAN bus is a serial, multi-master communication system. It sends data one bit at a time over a shared communication line. Any node (device) on the network can begin transmitting when the bus is free. A common baud rate, such as 500 kbps, means the bus can carry up to 500,000 bits per second. This includes all parts of the CAN message, including identifiers, control fields, data, and error-checking bits.


Common baud rates include:

125 kbps - Often used for long cable runs or industrial systems

250 kbps - Used in mixed applications, including off-road and agricultural equipment

500 kbps - Standard in most automotive networks

1 Mbps - Used in high-speed or time-sensitive systems


Most CAN software allows the user to set the bus speed to match the requirements of the network. Influx Technology’s ReXdesk software, for example, includes a simple menu for selecting supported baud rates.

How many messages does every baud rate support?

The CAN bus supports data payloads of up to 8 bytes per message. However, larger messages take longer to transmit, which increases latency and reduces the total number of messages that can be sent per second.

At a bit rate of 1 Mbit/s, using the standard CAN format and an average payload of 4 bytes, the bus can transmit roughly 10,000 messages per second. If each message carries the full 8 bytes, this number drops to around 7,200 messages per second due to the increased transmission time per frame.




Estimating Message Timing

To calculate how long each bit takes to transmit, use the formula below. This helps you estimate how long a full message takes based on its size:

Once you know the bit time, you can work out how long a complete CAN frame takes to send by multiplying it by the number of bits in a frame.

A standard CAN frame (with 8 data bytes) is approximately 125 bits long.

So for example:

At 250 kbps → 1 bit = 4 µs → Frame time = 4 × 125 = 500 µs

At 500 kbps → 1 bit = 2 µs → Frame time = 2 × 125 = 250 µs

Calculating Bus Load

Once you know how many messages you're sending per second and how many bytes are in each message, you can calculate the total data load (in bytes per second). This is the value you'll use to calculate the bus load.

If you're sending 500 messages per second, each with 4 bytes of data: 500×4=2000 bytes per second

Bus load shows how much of the bus bandwidth is being used. It’s expressed as a percentage and calculated using.

In real systems, CAN buses often operate reliably at up to 70–80% load, especially when using high-priority messages.

Estimating Bus Load from Mixed Message Intervals

To work out how much load your CAN bus is handling, you need to know how many bits are being placed on the bus each second. That means looking at:

• How often frames are sent

• How many frames are sent each time

• How many bits each frame takes on the bus

  
  

  For example, let’s assume each CAN frame is around 76 bits, this includes not just your data, but also the arbitration ID, control bits, CRC, and other overhead. That’s a common estimate when sending 32 bits (4 bytes) of actual data.

Interval	Frames	Formula	Bits/sec
5 missliseconds	5	(1 ÷ 0.005) × 5 × 76	76,000
10 missliseconds	5	(1 ÷ 0.010) × 5 × 76	38,000
100 missliseconds	5	(1 ÷ 0.100) × 5 × 76	3,800
		Total Bits per Second	117,800

So in total, your system is trying to place 117,800 bits per second on the CAN bus.

Calculating Bus Load

At 250 kbps

At 500 kbps

So at 250 kbps, you're using nearly half of the bus capacity. At 500 kbps, you’re using less than a quarter, leaving plenty of room for other traffic.

Note: Don’t confuse this with the earlier formula that used bits per second directly. Both versions are correct, they just start from different points.

• If you already know the bytes per second, use the formula above (and multiply by 8 to convert to bits).

• If you’ve already calculated bits per second, you can skip the byte conversion and divide directly by the bit rate.

The image below shows the active logging and trace viewer for Influx Technology's Rebel LT and CT series. It displays key parameters such as bit rate, total, per-second bus load, and message activity. You can also monitor transmitted and received (Rx/Tx) messages, along with error frames, including their frequency and overall load.

How Baud Rate Affects Cable Length

In a CAN bus system, there's a trade-off between baud rate and cable length. The higher the baud rate, the shorter the cable can be. This is because at faster speeds, each bit takes less time to transmit, so the signal has less time to travel along the cable and settle before the next bit starts.

If the cable is too long for the selected baud rate, you can run into issues like signal reflections, timing errors, or data loss, especially if the network isn't properly terminated.

Baud rate	Max Cable Length
1Mbit/s	30m - 40m
800 kbit/s	50m
500 kbit/s	100m - 110m
250 kbit/s	240m - 250m
125 kbit/s	500 m

These are typical values based on industry practice and assume proper termination and high-quality cable.

Understanding how baud rate, bit rate, and bus load work together is key to building a reliable CAN network. Whether you're troubleshooting timing issues, scaling up your system, or simply trying to get the most out of your existing setup. Getting these fundamentals right matters.

At Influx Technology, we build data loggers that take the guesswork out of working with CAN bus timing. Whether you're fine-tuning baud rates, monitoring bit-level performance, or tracking real-world bus load, our tools are designed to give you clear, accurate insights.

Explore our full range of CAN bus data loggers here.

Disclaimer :

The terms bit rate and baud rate are often used interchangeably in CAN bus discussions, but this differs from their traditional definitions in other communication systems. Historically, baud rate referred to the number of signal changes (symbols) per second, particularly in systems using modulation techniques like AM (Amplitude Modulation) or FM (Frequency Modulation), where each symbol could represent multiple bits.

CAN, uses non-return-to-zero (NRZ) encoding, where each bit corresponds to a single signal level. This means the baud rate and bit rate are effectively the same. While this doesn’t align perfectly with classical definitions, the term baud rate has become standard in the CAN community due to legacy usage.