Oh but it depends so much on the acoustics of the room where you're singing, the particular song, and the amount of background noise....

I've practised songs in my living room and written down the key or starting note and then tried singing the songs in the same key in a pub or club room and it just doesn't work.

Working out what the range of the song is in advance and checking your highest and lowest notes in the venue before you sing can help.

Kitty