The COBE detection of microwave anisotropies provides the best way of
fixing the amplitude of cosmological fluctuations on the largest scale
s. This normalization is usually given for an n = 1 spectrum, includin
g only the anisotropy caused by the Sachs-Wolfe effect. This is certai
nly not a good approximation for a model containing any reasonable amo
unt of baryonic matter. In fact, even tilted Sachs-Wolfe spectra are n
ot a good fit to models like cold dark matter (CDM). Here, we normaliz
e standard CDM (sCDM) to the two-year COBE data and quote the best amp
litude in terms of the conventionally used measures of power. We also
give normalizations for some specific variants of this standard model,
and we indicate how the normalization depends on the assumed values o
f n, OMEGA(B), and H0. For sCDM we find [Q] = 19.9 +/- 1.5 muK, corres
ponding to sigma8 = 1.34 +/- 0.10, with the normalization at large sca
les being B = (8.16 +/- 1.04) x 10(5) (h-1 Mpc)4, and other numbers gi
ven in the table. The measured rms temperature fluctuation smoothed on
10-degrees is a little low relative to this normalization. This is ma
inly due to the low quadrupole in the data: when the quadrupole is rem
oved, the measured value of sigma(10-degrees) is quite consistent with
the best-fitting [Q]. The use of [Q] should be preferred over sigma(1
0-degrees), when its value can be determined for a particular theory,
since it makes full use of the data.