We present the first quantitative theoretical results for the spatial distribution and flux levels of fundamental (fp) and second harmonic (2fp) plasma radiation generated in Earth's foreshock by beam-driven Langmuir waves. The theory predicts that both the fp and 2fp source regions typically extend over several hundred Earth radii (RE) along the tangent magnetic field line. In the direction perpendicular to the magnetic tangent, however, the source regions are more localized, with the peak emission confined to ≲10RE for 2fp radiation and ≲1RE for fp radiation. The flux levels predicted by our model are in close agreement with the levels measured in situ by various spacecraft, with typical values ~10-14W m-2 for 2fp radiation. The fp flux densities are typically 2--3 orders of magnitude lower.