  Determination of the magnetic field strength in the interstellar medium is
one of the most complex tasks of contemporary astrophysics. We can only
estimate the order of magnitude of the magnetic field strength by using a few
very limited methods. Besides Zeeman effect and Faraday rotation, the
equipartition or the minimum-energy calculation is a widespread method for
estimating magnetic field strength and energy contained in the magnetic field
and cosmic ray particles by using only the radio synchrotron emission. Despite
of its approximate character, it remains a useful tool, especially when there
is no other data about the magnetic field in a source. In this paper we give a
modified calculation which we think is more appropriate for estimating magnetic
field strengths and energetics in supernova remnants (SNRs). Finally, we
present calculated estimates of the magnetic field strengths for all Galactic
SNRs for which the necessary observational data are available. The web
application for calculation of the magnetic field strength of SNRs is available
at http://poincare.matf.bg.ac.rs/~arbo/eqp/.
