# How to Calculate the Fiber-Optic Cable Power Budget for EX Series Switches

To ensure that fiber-optic connections have sufficient power for correct operation, calculate the link's power budget when planning fiber-optic cable layout and distances to ensure that fiber-optic connections have sufficient power for correct operation. The power budget is the maximum amount of power the link can transmit. When you calculate the power budget, you use a worst-case analysis to provide a margin of error, even though all the parts of an actual system do not operate at the worst-case levels.

To calculate the worst-case estimate for fiber-optic
cable power budget (*P _{B}*) for the link:

- Determine values for the link's minimum transmitter power
(
*P*) and minimum receiver sensitivity (_{T}*P*). For example, here, (_{R}*P*) and (_{T}*P*) are measured in decibels, and decibels are referred to one milliwatt (dBm)._{R}*P*= – 15 dBm_{T}*P*= – 28 dBm_{R}**Note**See the specifications for your transmitter and receiver to find the minimum transmitter power and minimum receiver sensitivity.

- Calculate the power budget (
*P*) by subtracting (_{B}*P*) from (_{R}*P*):_{T}– 15 dBm – (–28 dBm) = 13 dBm