  The size of the stable elementary particles is investigated with the standing
wave model. The particle size follows from the magnitude of the radiation
pressure. It is shown that the outward directed radiation pressure is balanced
by the inward directed elastic force per unit area in the cubic nuclear
lattice, provided that the sidelength of the lattice is 10^(-13) cm, which
agrees with the measured radius of the proton r = 0.8 \times 10^(-13) cm,
within the uncertainty of the parameters.
