I don't really care about the numbers particularly-- it was an awesome demonstration where four avenues of the city were blocked by marchers and solidarity was amazing.
But the reality is good enough without mythmaking. I was doing police observing block by block as First Avenue filled. It got up to 72nd Avenue with pens filled. The police ran out of metal pens and began opening them up to squeeze more people in streets closer to the rally site. So you probably had more than 7000 per block squeezed in. I'd assume about double the crowd that was on First Avenue were on the side streets, so that adds up probably to forty to fifty blocks of people grand total -- an amazing number given the width of NYC Avenues. I'd bet on 300-500,000 folks, which is plenty good enough for me.
-- Nathan Newman