  The Laser Interferometer Space Antenna (LISA) will open the mHz band of the
gravitational wave spectrum for exploration. Sensitivity curves are a useful
tool for surveying the types of sources that can be detected by the LISA
mission. Here we describe how the sensitivity curve is constructed, and how it
can be used to compute the signal-to-noise ratio for a wide range of binary
systems. We adopt the 2018 LISA Phase-0 reference design parameters. We
consider both sky-averaged sensitivities, and the sensitivity to sources at
particular sky locations. The calculations are included in a publicly available
{\em Python} notebook.
