So how many was it?

Pajamas Media's Charlie Martin has some estimates of the crowd size at the September 12 rally in Washington, DC.

To summarize:

Rumored number	2 million
“People meter” count	1.5 million
Eight “Pennsylvania Avenues” full of people	800 thousand
Grant Memorial area by Park Service method	250 thousand
Legacy media reports	70 thousand

Average all of those and we get 900,000 plus (924,000). Throw out the outliers, we get 850,000. And remember that the 1.5 million was a real count; it’s inherently a more believable number. Our estimate should be “pulled” upward by that.

Conclusion: probably well more than 850,000 in the crowd.

Which is a lot of people.

I'd say throw out the extreme values, too. At the very least, assign them very large margins of error. My initial wild guess was about 750 K. If the 1.5 million count is pretty close to accurate, the most probable number creeps upward quite a bit.