We study the O(4) Wilson-Fisher fixed point in 2+1 dimensions in fixed large-charge sectors identified by products of two spin-j representations (j_{L},j_{R}). Using effective field theory we derive a formula for the conformal dimensions D(j_{L},j_{R}) of the leading operator in terms of two constants, c_{3/2} and c_{1/2}, when the sum j_{L}+j_{R} is much larger than the difference |j_{L}-j_{R}|. We compute D(j_{L},j_{R}) when j_{L}=j_{R} with Monte Carlo calculations in a discrete formulation of the O(4) lattice field theory, and show excellent agreement with the predicted formula and estimate c_{3/2}=1.068(4) and c_{1/2}=0.083(3).