NY has a 9" minimum length and since the DEC defines minimu length this way:
"Minimum Length means the greatest possible length measured from the tip of the fish's snout to the tip of the tail. The mouth may be open or closed and the tail may be spread or compressed in order to achieve the greatest length."
I lay them down and measure from the bottom lip to tip of tail.. I fish crappie for the table, not for sport, so however I can legally measure them and have them meet the 9" minimum, that's how I do it. Most times I don't need to measure because they are either dinky enough or big enough that they don't need to be measured - so I keep or release based on knowing big a keeper is from experience.