  We show that the correction-to-scaling exponents in two-dimensional
percolation are bounded by Omega <= 72/91, omega = D Omega <= 3/2, and Delta_1
= nu omega <= 2, based upon Cardy's result for the critical crossing
probability on an annulus. The upper bounds are consistent with many previous
measurements of site percolation on square and triangular lattices, and new
measurements for bond percolation presented here, suggesting this result is
exact. A scaling form evidently applicable to site percolation is also found.
