How many torpedo boats would overmatch Graf Spee at the River Plate?

How many torpedo boats would be needed to guarantee victory at the Battle of the River Plate?

For an overmatch rather than a chance of success, roughly a dozen to two dozen torpedo boats would be needed.

A small torpedo-boat force could still damage Admiral Graf Spee if it gained a favourable approach and scored lucky hits. A definite victory demands enough boats to absorb losses and continue the attack. That raises the estimate from a merely plausible force to roughly a dozen or two dozen craft. A requirement for certainty drives force numbers far above the minimum needed for a chance of success.