Calculate received optical power at a fiber receiver given transmit power and losses.
Optical power meters typically read out in dBm, computed as P(dBm) = 10·log10(P_mW). Comparing a measured power level against common reference points — typical transmitter output (often around 0 dBm for SFP+ optics), typical receiver sensitivity (around -17 to -22 dBm), and receiver overload thresholds (power too high can saturate a receiver just as easily as too little can starve it) — helps quickly assess whether a measured link power reading is healthy.
Power in dBm
P(dBm) = 10 × log10(P_mW)
Yes — receivers have a maximum input power (overload threshold), typically around -3 dBm or higher for many SFP/SFP+ optics, beyond which the receiver's photodiode can saturate and cause errors, so short fiber runs sometimes need an attenuator even though power is technically 'plenty'.
Many common single-mode and multimode SFP/SFP+ transceivers launch around -1 to +2 dBm, though DWDM and long-haul optics can launch significantly higher (often 0 to +7 dBm or more) to overcome greater fiber attenuation over distance.
Because it represents the minimum usable power, which after traveling through fiber and connectors is inevitably far less than 1 mW (0 dBm) — a more negative sensitivity number (e.g. -28 dBm vs -17 dBm) means a more sensitive receiver that can detect a weaker signal.
Measure or estimate your transmitter's launch power in dBm here, then use the Fiber Loss Budget or Optical Budget calculators to see whether the resulting received power, after subtracting expected losses, stays comfortably above your receiver's sensitivity floor.