Distribution of fractional widths (∆R/R) for exo-Kuiper belts (blue) and protoplanetary rings (orange). The top panel shows the histogram of widths while the bottom panel shows the 2D distribution of fractional widths and central radii. The solid lines (top panel) and filled contours (bottom panel) represent kernel density estimations using a Gaussian kernel and a bandwidth chosen following Scott’s rule (Scott 2015). The green dashed line and green circle represent the Kuiper belt fractional width and central radius. The belts with gaps around HD 92945, HD 107146 and HD 206893 are represented by ⊚ symbols.