Earth-like planets were defined to have a radius 0.9 < R⨂ < 1.2 and a semi-major axis 0.8 AU < a < 1.2 AU. Only G-type stars are considered with this definition.
2.7% of G-type stars should have an earthlike planet (and 6.36% of all stars should have an earthlike planet by the above definition).
From Why We Haven't Found Any Earthlike Planets: