The maximum amplitudes of solar activity cycles are found to be well anticorrelated (r = -0.72) with the newly defined solar cycle lengths three cycles before (at lag -3) in 13-month running mean sunspot numbers during the past 190 years. This result could be used for predicting the maximum sunspot numbers. The amplitudes of Cycles 24and 25 are estimated to be 149.5±27.6 and 144.3±27.6, respectively.