title_body: How should one chose the correct motor KV for a build? For a 5 inch, 4S build, the general advice is to go 2300-2750KV. For the same size but 6S, it should be ~1800KV. However the same motors could be used on a 4S 7 inch quad. And all of this scaling seems to go into the window when moving onto something like whoops or toothpicks, and up to X-class.
  
  How should one choose the most appropriate KV for their intended build? Is there a formula to use, or is it just learned through experience?
upvoted_answer: I think it’s learned through experience and it can also be roughly figured out using this table based on frame and propellor size:
  
      ╔══════════════════╦═══════════════╦═════════════════╦══════════════════╗
      ║ Frame size       ║ Prop size     ║ Motor size      ║ KV               ║
      ╠══════════════════╬═══════════════╬═════════════════╬══════════════════╣
      ║ 150mm or smaller ║ 3" or smaller ║ 1306 or smaller ║ 3000KV or higher ║
      ╠══════════════════╬═══════════════╬═════════════════╬══════════════════╣
      ║ 180mm            ║ 4"            ║ 1806            ║ 2600KV           ║
      ╠══════════════════╬═══════════════╬═════════════════╬══════════════════╣
      ║ 210mm            ║ 5"            ║ 2204-2206       ║ 2300KV-2600KV    ║
      ╠══════════════════╬═══════════════╬═════════════════╬══════════════════╣
      ║ 250mm            ║ 6"            ║ 2204-2208       ║ 2000KV-2300KV    ║
      ╠══════════════════╬═══════════════╬═════════════════╬══════════════════╣
      ║ 350mm            ║ 7"            ║ 2208            ║ 1600KV           ║
      ╠══════════════════╬═══════════════╬═════════════════╬══════════════════╣
      ║ 450mm            ║ 8", 9", 10"   ║ 2212 or larger  ║ 1000KV or lower  ║
      ╚══════════════════╩═══════════════╩═════════════════╩══════════════════╝
  
  
  (table source)