  We propose a conceptually and computationally simple method to evaluate the
neutrinos emitted by supernova remnants using the observed gamma-ray spectrum.
The proposed method does not require any preliminary parametrization of the
gamma ray flux; the gamma ray data can be used as an input. In this way, we are
able to propagate easily the observational errors and to understand how well
the neutrino flux and the signal in neutrino telescopes can be constrained by
gamma-ray data. We discuss the various possible sources of theoretical and
systematical uncertainties (e.g., neutrino oscillation parameters, hadronic
modeling, etc.), obtaining an estimate of the accuracy of our calculation.
Furthermore, we apply our approach to the supernova remnant RX J1713.7-3946,
showing that neutrino emission is very-well constrained by the H.E.S.S.
gamma-ray data: indeed, the accuracy of our prediction is limited by
theoretical uncertainties. Neutrinos from RX J1713.7-3946 can be detected with
an exposure of the order km^2 year, provided that the detection threshold in
future neutrino telescopes will be equal to about 1 TeV.
