International
Tables for Crystallography Volume C Mathematical, physical and chemical tables Edited by E. Prince © International Union of Crystallography 2006 
International Tables for Crystallography (2006). Vol. C, ch. 6.1, p. 590

The reflecting power of a small crystal of volume ΔV, rotated at angular velocity ω through a Bragg reflection, defined as the ratio of ω times the reflected energy to the incidentbeam intensity, is where is the unitcell volume. This expression, which assumes negligible absorption, shows that the integrated intensity is proportional to the crystal volume. The maximum intensity is proportional to (ΔV)^{2}, but the angular width of the reflecting region varies inversely as ΔV.
In the kinematic theory of diffraction, it is assumed that the crystal is comprised of small domains of perfect crystals for which the intensities are additive. In that case, (6.1.1.95) applies also to finite crystals.