  Filaments and sheets are striking visual patterns in cosmic web. The maximum
extent of these large-scale structures are difficult to determine due to their
structural variety and complexity. We construct a volume-limited sample of
galaxies in a cubic region from the SDSS, divide it into smaller subcubes and
shuffle them around. We quantify the average filamentarity and planarity in the
three-dimensional galaxy distribution as a function of the density threshold
and compare them with those from the shuffled realizations of the original
data. The analysis is repeated for different shuffling lengths by varying the
size of the subcubes. The average filamentarity and planarity in the shuffled
data show a significant reduction when the shuffling scales are smaller than
the maximum size of the genuine filaments and sheets. We observe a
statistically significant reduction in these statistical measures even at a
shuffling scale of $\sim 130 \,$Mpc, indicating that the filaments and sheets
in three dimensions can extend up to this length scale. They may extend to
somewhat larger length scales that are missed by our analysis due to the
limited size of the SDSS data cube. We expect to determine these length scales
by applying this method to deeper and larger surveys in future.
