A voltage calibration method, a memory storage device, and a memory control circuit unit are disclosed. The method includes: reading first data from a first physical unit using a first read voltage level and reading second data from at least one second physical unit using a second read voltage level; obtaining count information reflecting a total number of memory cells meeting a default condition in the first physical unit and the at least one second physical unit according to the first data and the second data; and calibrating the first read voltage level according to the count information.