  Neutron stars may sustain a non-axisymmetric deformation due to magnetic
distortion and are potential sources of continuous gravitational waves (GWs)
for ground-based interferometric detectors. With decades of searches using
available GW detectors, no evidence of a GW signal from any pulsar has been
observed. Progressively stringent upper limits of ellipticity have been placed
on Galactic pulsars. In this work, we use the ellipticity inferred from the
putative millisecond magnetars in short gamma-ray bursts (SGRBs) to estimate
their detectability by current and future GW detectors. For $\sim 1$ ms
magnetars inferred from the SGRB data, the detection horizon is $\sim 30$ Mpc
and $\sim 600$ Mpc for advanced LIGO (aLIGO) and Einstein Telescope (ET),
respectively. Using the ellipticity of SGRB millisecond magnetars as
calibration, we estimate the ellipticity and gravitational wave strain of
Galactic pulsars and magnetars assuming that the ellipticity is
magnetic-distortion-induced. We find that the results are consistent with the
null detection results of Galactic pulsars and magnetars with the aLIGO O1. We
further predict that the GW signals from these pulsars/magnetars may not be
detectable by the currently designed aLIGO detector. The ET detector may be
able to detect some relatively low frequency signals ($<50$ Hz) from some of
these pulsars. Limited by its design sensitivity, the eLISA detector seems not
suitable for detecting the signals from Galactic pulsars and magnetars.
