CAN Bus Termination Resistor

Rterm = Z0 / 2

Quick answer

This calculator solves R_term = Z₀ / 2 (at each end of the bus, total = Z₀) for Termination Resistor. With Cable Impedance 1.03 kΩ, the result is 0.515 kΩ. It solves in 2 directions, so you can enter the values you have and get the one you need.

Calculator

Termination Resistor (Ω)
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Formula

R_term = Z₀ / 2 (at each end of the bus, total = Z₀)

Description

CAN bus requires two termination resistors, one at each end of the bus, to prevent signal reflections. Each resistor is nominally half the cable characteristic impedance, so the two in parallel equal Z₀. Standard CAN bus cable has Z₀ = 120 Ω, so each termination resistor is 60 Ω. However, the ISO 11898 standard specifies 120 Ω at each end (not 60 Ω), because the bus is driven differentially and each termination bridges CAN_H to CAN_L. The parallel combination of two 120 Ω resistors provides the correct DC bias and AC termination.

Variables

  • R_term — Termination resistor value at each bus end (Ω)
  • Z₀ — Characteristic impedance of the CAN bus cable (Ω)

Practical Notes

Standard CAN: 120 Ω termination at each end of the bus. CAN FD uses the same termination. Split termination (two 60 Ω resistors with a capacitor to ground at the midpoint) provides better EMI performance by filtering common-mode noise. Missing or incorrect termination causes reflections, bit errors, and can prevent communication entirely. The total resistance measured between CAN_H and CAN_L with both terminators in place should be about 60 Ω.

Symbols and units

Symbol Meaning Default unit Accepted units
Rterm Termination Resistor Ω mΩ, Ω, kΩ, MΩ
Z0 Cable Impedance Ω mΩ, Ω, kΩ, MΩ

Step by step

  1. 1. What you know: Cable Impedance 1.03 kΩ
  2. 2. The relation: R_term = Z₀ / 2 (at each end of the bus, total = Z₀)
  3. 3. Substitute: Z0 = 1.03 kΩ
  4. 4. Result: Termination Resistor = 0.515 kΩ

Nearest standard component values

Series Nearest value Error
E12 0.47 kΩ 8.7%
E24 0.51 kΩ 0.97%

Worked examples

Minimum range

Given: Cable Impedance 2.2 Ω

Result: Termination Resistor = 1.1 Ω

Low range

Given: Cable Impedance 22 Ω

Result: Termination Resistor = 11 Ω

Typical

Given: Cable Impedance 1.03 kΩ

Result: Termination Resistor = 0.515 kΩ

High range

Given: Cable Impedance 10.3 kΩ

Result: Termination Resistor = 5.15 kΩ

Maximum range

Given: Cable Impedance 103 kΩ

Result: Termination Resistor = 51.5 kΩ

Solving for each variable

Solve for Termination Resistor

Cable Impedance 2.2 Ω → 1.1 Ω

Solve for Cable Impedance

Termination Resistor 1 Ω → 2 Ω

How Termination Resistor changes with Cable Impedance

Cable Impedance (input) Termination Resistor (result)
0.227 kΩ 113.5 Ω
0.5675 kΩ 0.2838 kΩ
1.135 kΩ 0.5675 kΩ
1.703 kΩ 0.8513 kΩ
2.27 kΩ 1.135 kΩ
3.405 kΩ 1.703 kΩ
4.54 kΩ 2.27 kΩ
9.08 kΩ 4.54 kΩ
15.89 kΩ 7.945 kΩ
22.7 kΩ 11.35 kΩ

The same result in other units

Unit Value
mΩ 515000
Ω 515
kΩ 0.515
MΩ 0.000515

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Frequently asked questions

How do you calculate CAN Bus Termination Resistor?

Use R_term = Z₀ / 2 (at each end of the bus, total = Z₀). With Cable Impedance 1.03 kΩ, Termination Resistor works out to 0.515 kΩ.

What is the formula for CAN Bus Termination Resistor?

The formula is R_term = Z₀ / 2 (at each end of the bus, total = Z₀). CAN bus requires two termination resistors, one at each end of the bus, to prevent signal reflections.

How do you find Cable Impedance when you know the other values?

Rearrange for Cable Impedance: with Termination Resistor 1 Ω, Cable Impedance is 2 Ω.

What units does CAN Bus Termination Resistor use?

Termination Resistor is shown in mΩ, Ω, kΩ, MΩ. Values are held in SI base units internally, so you can mix prefixes without converting by hand.

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