The answer is in the tens of millions but no one really knows beyond that. The Chinese population wasn’t well known at the time and the records from that era are poor at best. However, the Chinese government acknowledges that there were serious consequences to the economy and population during the great leap forward (here’s their English writings on it) and as Wikipedia states, a 3.5% death toll would have caused tens of millions of deaths and be considered a modest famine. Some of the Western estimates are vast exaggerations, but the majority of them (especially modern day) are reasonable.