  We perform a precise calculation of the decay rate of the electroweak vacuum
in the standard model as well as in models beyond the standard model. We use a
recently-developed technique to calculate the decay rate of a false vacuum,
which provides a gauge invariant calculation of the decay rate at the one-loop
level. We give a prescription to take into account the zero modes in
association with translational, dilatational, and gauge symmetries. We
calculate the decay rate per unit volume, $\gamma$, by using an analytic
formula. The decay rate of the electroweak vacuum in the standard model is
estimated to be $\log_{10}\gamma\times{\rm Gyr~Gpc^3} =
-582^{+40~+184~+144~+2}_{-45~-329~-218~-1}$, where the 1st, 2nd, 3rd, and 4th
errors are due to the uncertainties of the Higgs mass, the top quark mass, the
strong coupling constant and the choice of the renormalization scale,
respectively. The analytic formula of the decay rate, as well as its fitting
formula given in this paper, is also applicable to models that exhibit a
classical scale invariance at a high energy scale. As an example, we consider
extra fermions that couple to the standard model Higgs boson, and discuss their
effects on the decay rate of the electroweak vacuum.
