  Recent measurements in two-particle correlations in $p$+Pb collisions suggest
collective behavior reminiscent of that observed in Pb+Pb. Femtoscopic
measurements may provide useful insight on this behavior because they image the
spatio-temporal size of the particle emitting region. This proceeding presents
identical-pion Hanbury Brown and Twiss (HBT) measurements from ATLAS using one-
and three-dimensional correlation functions. Pions are identified using
$\text{d}E/\text{d}x$ measured in the pixel detector. Correlation functions and
the resulting HBT radii are shown as a function of pair momentum ($k_{\rm T}$)
and collision centrality.
