CAN Bus Termination & Stub Calculator
Verify CAN/CAN-FD termination, max stub length, and bus length for specified bit rate. Prevents reflections on automotive and industrial buses.
How to Use
- Enter CAN bit rate (500 kbps classic, up to 8 Mbps CAN-FD).
- Tool gives max bus length and max stub length for that bit rate.
Show Work
CAN Spec Limits
History of CAN
Robert Bosch GmbH developed CAN (Controller Area Network) in 1983 for automotive in-vehicle networking; Mercedes-Benz first deployed it in the 1991 S-Class. CAN's differential twisted-pair with 120-ohm termination became ISO 11898-2 in 1993. CAN-FD (Flexible Data Rate, 2012) doubled then quadrupled the data rate. Modern vehicles run multiple segmented CAN buses alongside Ethernet and LIN, but CAN remains the safety-critical workhorse for powertrain, brake, and airbag signaling.
About This Calculator
Enter bit rate, node count, and cable velocity factor (0.66 for PVC-insulated twisted pair, 0.8 for foam dielectric). The tool computes max bus length and max stub length per ISO 11898-2 guidance.
Terminate the bus with 120Ω at BOTH ends (never in the middle). For EMI-sensitive designs use split termination (2×60Ω + 4.7nF to ground). Add 10-47 kΩ bias to Vdd/Vss on each terminator for reliable dominant/recessive arbitration. Everything runs client-side.
Frequently Asked Questions
Why 120Ω?
CAN uses twisted pair with characteristic impedance Z₀ = 120Ω. Terminators at each end match this to prevent reflections. Two 60Ω in parallel (one at each bus end) = 120Ω.
Split termination?
Two 60Ω resistors per end with a small cap to ground between them. Improves EMI performance by giving common-mode signals a path to ground. Typical 60Ω + 60Ω + 4.7nF to GND at midpoint.
Max stubs?
Stub = node-to-bus tap. Max length scales inversely with bit rate: 0.3m at 500 kbps, 0.03m (3 cm!) at 5 Mbps CAN-FD. Long stubs cause reflections and bit errors.
Common Use Cases
Automotive 500 kbps
Max bus 40 m, max stub 0.3 m. Standard OBD-II / powertrain CAN.
Industrial 250 kbps
Max bus 250 m with shielded cable. Factory automation, CANopen.
CAN-FD 5 Mbps
Max bus 10 m, max stub 3 cm. Automotive high-speed ECU comms.
Last updated: