CAN / CAN FD Frame Length and Transmission Time Calculator
CAN / CAN FD Frame Length and Transmission Time Calculator
Compute frame bit count (including bit stuffing) and transmission time from baud rate and frame format for bus load estimation.
Frame and Baud Rate
Results and Frame Waveform
Segments are proportional to transmission time; not an exact waveform. With BRS on, Data/CRC segments are shortened by the accelerated baud rate.
Arbitration rate: 1 Mbps; Data rate: 5 Mbps
Overview
This tool calculates the bit count and transmission time of a CAN or CAN FD frame from its bit rate and format. It supports exact Classical CAN calculations from actual payload data, worst-case estimates, Linux CAN command generation and a proportional frame-structure diagram.
Features
- Exact calculation: applies Classical CAN bit-stuffing rules to the actual frame and calculates CRC-15
- Estimate mode: uses a worst-case stuffing formula for CAN FD or quick planning
- Linux commands: generates
cangen,cansendand samplecandumpoutput - Frame diagram: displays SOF, identifier, control, data, CRC, ACK and EOF; CAN FD shows arbitration and data phases separately
Input Parameters
Frame Format
| Parameter | Description |
|---|---|
| Protocol | Classical CAN 2.0 or CAN FD |
| Identifier format | Standard 11-bit or extended 29-bit identifier |
| BRS | CAN FD bit-rate switching; the data phase uses the faster configured rate |
| Message ID | Hexadecimal; 0x000–0x7FF for standard or 0x00000000–0x1FFFFFFF for extended |
| DLC | 0–8 for CAN 2.0; 0–8, 12, 16, 20, 24, 32, 48, 64 for CAN FD |
| Payload | Space-separated hexadecimal bytes, for example 01 02 03 04 |
Bit Rates
| Parameter | Description |
|---|---|
| Arbitration bit rate | Nominal phase rate in bit/s; quick values include 125k, 250k, 500k and 1M |
| Data bit rate | CAN FD data-phase rate when BRS is enabled; quick values include 1M, 2M, 4M, 5M and 8M |
Calculation Mode
| Mode | Description |
|---|---|
| Exact | Classical CAN only; uses the actual payload, bit-stuffing rules and calculated CRC |
| Estimate | Worst-case stuffing overhead, suitable for CAN FD and quick planning |
Results
| Result | Description |
|---|---|
| Total frame bits | Bit count including stuffing and inter-frame space |
| Transmission time | μs and ms values for timing and load calculations |
| Frame diagram | Proportional SOF, ID, control, data, CRC, ACK, EOF and IFS sections |
Exact Classical CAN Details
Exact mode also reports:
- Original bit count before stuffing
- Bit count after stuffing
- Number of inserted stuff bits
- Calculated CRC-15 value
Generated Linux Commands
| Command | Use |
|---|---|
cangen | Periodic transmission with a configurable interval |
cansend | Send one frame |
candump | Example receive output |
Bus-Load Estimate
For a frame transmitted every period T:
Bus load ≈ (frame transmission time / T) × 100%The result view shows an example for the selected transmission period.
CAN Frame Structure
Classical CAN Standard Frame
SOF + ID(11) + RTR + IDE + r0 + DLC(4) + Data(0–64) + CRC(15) + DEL + ACK + DEL + EOF(7) + IFS(3)Classical CAN Extended Frame
SOF + ID(29) + SRR + IDE + r1 + r0 + DLC(4) + Data(0–64) + CRC(15) + DEL + ACK + DEL + EOF(7) + IFS(3)CAN FD with BRS
CAN FD can use two rates in one frame:
- Arbitration phase: SOF, identifier and relevant control fields use the arbitration bit rate.
- Data phase: payload and CRC use the faster data bit rate when BRS is enabled.
Bit Stuffing
CAN inserts an opposite-polarity stuff bit after five consecutive identical bits.
- Applied from SOF through the CRC sequence
- Not applied to CRC delimiter, ACK, ACK delimiter, EOF or IFS
- A common worst-case estimate adds approximately 20% overhead
Exact stuffing depends on the complete identifier, control fields, payload and CRC; it cannot be inferred from DLC alone.
Linux Command Reference
cangen Options
| Option | Description |
|---|---|
-I | CAN identifier in hexadecimal |
-e | Extended identifier |
-D | Payload in hexadecimal |
-L | DLC |
-g | Transmission interval in milliseconds |
-f | CAN FD frame |
-b | Enable bit-rate switching |
cansend Examples
# Classical CAN standard frame
cansend can0 123#0102030405060708
# Classical CAN extended frame
cansend can0 18DAF110#0102030405060708
# CAN FD with BRS
cansend can0 123##10102030405060708
# CAN FD without BRS
cansend can0 123##40102030405060708FAQ
What Is Required for an Exact Calculation?
- Enter the complete payload.
- Payload length must match the DLC.
- Exact mode currently supports Classical CAN; CAN FD uses estimate mode.
What Happens if Payload Length Does Not Match DLC?
Exact mode displays a warning and falls back to estimation. Data beyond the selected DLC may be truncated by the input control.
Which Mode Should I Use?
- Use Exact when the complete Classical CAN payload is known.
- Use Estimate when only the DLC is known or a quick upper-bound estimate is sufficient.
- Use Estimate for CAN FD until exact CAN FD stuffing is implemented.