Mean bubble diameter as a function of $\overline{x}$. We adopt the characteristic bubble size measured using the mean-free-path method in Lu et al. (2024) and assume z = 8 (there is minimal impact on the physical sizes over the epoch of reionization, z∼6−10). We show bubble diameter in arcmin on the plane-of-the-sky on the left axis and along the line-of-sight in redshift width on the right axis. Gray lines mark the area of existing and upcoming spectroscopic surveys with JWST.