  We propose a measure of macroscopic coherence based on the degree of
disturbance caused by a coarse-grained measurement. Based on our measure, we
point out that recently proposed criteria of macroscopic coherence may lead to
inconsistent results when considering certain states such as a product of
microscopic superpositions. An inequality relation is proved that relates the
Wigner-Yanase-Dyson skew information and the measurement disturbance, providing
arguments as to why our approach is able to rule out such inconsistencies. We
show that our measure can also quantify the fragility of a quantum state to a
certain type of decoherence. Our work provides a general framework of
quantifying macroscopic coherence from an operational point of view, based on
the relationship between the precision of the measurement and disturbance of
the quantum state.
