When the angel measured the New Jerusalem with his golden rod, what figure did he record?

Answer: 12,000 stadia

The city lies foursquare; he measured it at 12,000 stadia (KJV: furlongs), its length, width and height being equal.

“The angel who spoke with me had a golden measuring rod to measure the city and its gates and walls. The city lies foursquare, with its width the same as its length. And he measured the city with the rod, and all its dimensions were equal—12,000 stadia in length and width and height.”— Revelation 21:15-16 (BSB)