  We introduce a novel way of measuring $H_0$ from a combination of independent
geometrical datasets, with no need of calibration nor of the choice of a
cosmological model. We build on the {\it distance duality relation} which sets
the ratio of the luminosity and angular diameter distance to a fixed scaling in
redshift for any metric theory of gravity with standard photon propagation and
constitutes a founding block of any theory describing our Universe. Our method
provides the unprecedented possibility of determining $H_0$ from first
principles, unleashing the measurement of this fundamental constant from
calibration and assumption of a cosmological model. We find $H_0=69.5 \pm 1.7$
km/s/Mpc at $68\%$ C.L. showing that the Hubble constant can be constrained at
percent level with minimal assumptions.
