  We provide an easy method to obtain the kinetic energy fraction in
gravitational waves, generated during a cosmological first-order phase
transition, as a function of only the wall velocity and quantities that can be
determined from the particle physics model at the nucleation temperature. This
generalizes recent work that achieved this goal for detonations. Here we
present the corresponding results for deflagrations and hybrids. Unlike for
detonations, the sound speed in the symmetric phase also enters the analysis.
We perform a detailed comparison between our model-independent approach and
other approaches in the literature. We provide a Python code snippet to
determine the kinetic energy fraction $K$ as a function of the wall velocity,
the two speeds of sound and the strength parameter of the phase transition. We
also assess how realistic sizable deviations in speed of sound are close to the
phase transition temperature in a specific model.
