How Fast does Grass Grow?

While the time-lapse photography on the main grass growing page clearly shows ... grass growing ... it actually doesn't grow fast enough for the human eye to detect. In a week, grass may grow 2-6 inches (depending on temperature, humidity, time of year, etc.). So do the math - that works out to about a thousandth of in inch every 15-20 minutes ... would be hard to see! ;-)