This paper gives the first two moments of a wave field scattered by grazing incidence on a moderately rough surface. The expressions are derived for normally distributed surfaces with arbitrary spectrum, and are valid at depths that are large compared with the surface height. It is demonstrated that the first moment has a weak dependence on the surface fluctuation spectrum. The first moment is compared with Monte Carlo simulations, and gives close agreement. It is also shown that for a given degree of surface roughness the first moment retains the flat‐surface reflection property of being determined by the distance from an ‘‘image source,’’ i.e., the sum of the depths of source and receiver.