Traditionally, the meniscus bottom is taken as the fluid front when tracking the fluid motion in capillary, but in simulation studies, the thus-calculated motion curve deviates notably from the modified Lucas-Washburn equation. Here, we report that, by considering a volume equivalent of the meniscus part, the motion of the equivalent front agrees very well with the theoretical prediction; furthermore, such an effective fluid front can be directly represented by a specific position of the meniscus, which is independent of the capillary radius. These findings provide an accurate and practical method for describing the motion of the fluid front in capillary.