The equations Ed= 1/2 NJ2+const for demagnetizing energy and Hd=-NJ for average internal demagnetizing field (J is magnetization; N is demagnetizing factor, assumed constant) are central to multidomain (MD) theories of thermoremanence (TRM) and hysteresis. Theoretical calculations reported here, based on Rhodes and Rowlands' (1954) equations for Ed of an MD cube, test the variation of N with the number n of domains and with domain wall displacement x. For n even, Ed(x)-Ed(0) is nearly proportional to x2 or J2, so that N is practically constant (to ≈20% if n=2, ≈10% if n=4 and ≈5% if n=8) for 0≤J≤Js. This result reaffirms the validity of traditional MD rock magnetic theories. However, if n is small, N is significantly less than 4&pgr;/3 (the single-domain or n→∞ value); N≈2 for n=2 and (4&pgr;/3)-N) decreases as 1/n, so that n→4&pgr;/3 when n=8 or 10. Grains with n odd possess a spontaneous remanence even in the absence of wall pinning that is substantial (Jr≈0.1Js) for n=3 but decreases rapidly for larger n. This spontaneous remanence is a possible source of so-called pseudo-single-domain enhancement of TRM in small MD grains.