Acceptable dB loss for fiber depends on the component you're measuring: a single mated connector pair should lose no more than 0. 75 dB, a fusion splice should stay under 0. For each connector, we usually figure 0. The total. At TREND Networks, we are frequently asked how much loss is allowed when conducting testing on fiber optic cabling. Unfortunately, it is not a simple answer and depends on several factors. So, how can we know the loss value on the fiber optic link? This article will teach you how to calculate the loss in the fiber. Fiber loss, or attenuation, refers to the reduction in optical power as light travels through a fiber optic cable. While some loss is expected, excessive or unexpected loss can lead to poor performance, network downtime, and signal failure.