  We present distance scale measurements from the baryon acoustic oscillation
signal in the CMASS and LOWZ samples from the Data Release 12 of the Baryon
Oscillation Spectroscopic Survey (BOSS). The total volume probed is 14.5
Gpc$^3$, a 10 per cent increment from Data Release 11. From an analysis of the
spherically averaged correlation function, we infer a distance to $z=0.57$ of
$D_V(z)r^{\rm fid}_{\rm d}/r_ {\rm d}=2028\pm21$ Mpc and a distance to $z=0.32$
of $D_V(z)r^{\rm fid}_{\rm d}/r_{\rm d}=1264\pm22$ Mpc assuming a cosmology in
which $r^{\rm fid}_{\rm d}=147.10$ Mpc. From the anisotropic analysis, we find
an angular diameter distance to $z=0.57$ of $D_{\rm A}(z)r^{\rm fid}_{\rm
d}/r_{\rm d}=1401\pm21$ Mpc and a distance to $z=0.32$ of $981\pm20$ Mpc, a 1.5
per cent and 2.0 per cent measurement respectively. The Hubble parameter at
$z=0.57$ is $H(z)r_{\rm d}/r^{\rm fid}_{\rm d}=100.3\pm3.7$ km s$^{-1}$
Mpc$^{-1}$ and its value at $z=0.32$ is $79.2\pm5.6$ km s$^{-1}$ Mpc$^{-1}$, a
3.7 per cent and 7.1 per cent measurement respectively. These cosmic distance
scale constraints are in excellent agreement with a $\Lambda$CDM model with
cosmological parameters released by the recent Planck 2015 results.
