  We report on a scale determination with gradient-flow techniques on the $N_f
= 2 + 1 + 1$ HISQ ensembles generated by the MILC collaboration. The lattice
scale $w_0/a$, originally proposed by the BMW collaboration, is computed using
Symanzik flow at four lattice spacings ranging from 0.15 to 0.06 fm. With a
Taylor series ansatz, the results are simultaneously extrapolated to the
continuum and interpolated to physical quark masses. We give a preliminary
determination of the scale $w_0$ in physical units, along with associated
systematic errors, and compare with results from other groups. We also present
a first estimate of autocorrelation lengths as a function of flowtime for these
ensembles.
