I think a lot depends on context. I’ve only been asked this in public razzing environments where joking back is appropriate “why? are you really loose?” Or “your dad didn’t complain” If flirty, “play your cards right and maybe you’ll find out” works. Like others’ve said. If joking and flirty, “what I lack in length, I make up for in quickness” To your question, I wouldn’t give a number. Treat it as a vibe check and be confident. your dick is fine, bro.