BACnet Network Design Calculator

Network segments and routers from device count and location.

Total BACnet devices

Devices per trunk

Trunks per router

MS/TP Baud Rate

Number of floors

Tab to move between fields

MS/TP trunks required

BACnet/IP routers

Max token rotation (ms)250

Max poll cycle (ms)325

Within 2s poll limit1

Est. cable length (m)2,400

Trunks per floor1

Total MAC addresses58

How to Use This Calculator

Enter Total BACnet devices, Devices per trunk, and Trunks per router.
Select the MS/TP Baud Rate (9,600 / 19,200 / 38,400 / 76,800 bps) and enter the Number of floors.
Review MS/TP trunks required and BACnet/IP routers.
Use Max token rotation (ms) and Max poll cycle (ms), along with Within 2s poll limit, to check DDC responsiveness.
Check Est. cable length (m), Trunks per floor, and Total MAC addresses for the network layout.

How the result changes with Total BACnet devices

Total BACnet devices: Total number of BACnet MS/TP field devices (controllers, sensors, actuators) on the network.
Devices per trunk: Max devices per MS/TP trunk segment. ASHRAE 135 max is 32; 20-25 recommended for performance.
Trunks per router: Number of MS/TP trunks each BACnet/IP router can serve. Typical: 4-12 depending on hardware.
MS/TP Baud Rate: Select MS/TP baud rate. Higher baud = faster token rotation.
Number of floors: Building floors — used to estimate trunk distribution per floor.

MS/TP trunks required: Total trunk segments needed based on device count and per-trunk limit.
BACnet/IP routers: Number of BACnet/IP to MS/TP routers required.
Max token rotation (ms): Worst-case token passing time on the fullest trunk at the selected baud rate.
Max poll cycle (ms): Estimated maximum poll cycle including retry overhead. Should be < 2000ms for responsive DDC.
Within 2s poll limit: 1 = yes (acceptable), 0 = no (reduce devices per trunk or increase baud rate).
Est. cable length (m): Rough total cable estimate assuming 50m average between devices, max 1200m per trunk.
Trunks per floor: Average number of trunks per floor for balanced distribution.
Total MAC addresses: Total MAC addresses consumed by devices and router trunk ports.

Identify Input Parameters
4 parameters
Total BACnet devices = 50, Devices per trunk = 25, Trunks per router = 8, MS/TP Baud Rate = 3 = 5 input(s) provided
Calculate MS/TP trunks required
MS/TP trunks required
2 = 2
Calculate BACnet/IP routers
BACnet/IP routers
1 = 1
Calculate Max token rotation
Max token rotation = devicesOnFullTrunk * tokenTimePerDeviceMs
250 = 250
Calculate Max poll cycle
Max poll cycle = maxTokenRotationMs * 1.3
325 = 325