A measurement of the Hubble constant from angular diameter distances to two gravitational lenses.

The local expansion rate of the Universe is parametrized by the Hubble constant, [Formula: see text], the ratio between recession velocity and distance. Different techniques lead to inconsistent estimates of [Formula: see text] Observations of Type Ia supernovae (SNe) can be used to measure [Formula: see text], but this requires an external calibrator to convert relative distances to absolute ones. We use the angular diameter distance to strong gravitational lenses as a suitable calibrator, which is only weakly sensitive to cosmological assumptions. We determine the angular diameter distances to two gravitational lenses, [Formula: see text] and [Formula: see text] megaparsec, at redshifts [Formula: see text] and 0.6304. Using these absolute distances to calibrate 740 previously measured relative distances to SNe, we measure the Hubble constant to be [Formula: see text] kilometers per second per megaparsec.