Caliph Hamish Aw-Michty Ay-Ya-Bastard, Spiritual leader of Scottish State in England
OK all you bike buffs...
I bought a bike.
Not an exciting one like you have but a cheap elderly second hand thing.
I feel I'm probably a cheap elderly second hand thing so we'll make a good team.
It's probably an ordinary bike just styled a bit mountain bike but it would die if I showed it a hill.
It has the non-crossbar type of frame so it was presumably originally designed for a girl.
However... how high do I set the seat?
It's currently set to get both feet well planted on the ground but that makes peddling a dangerous exercise as I feel like I'm going to knee myself in the face (almost) (well not a chance but it's obviously too low).
What's the magic formula?
I just rode it home, about a mile, from our local bike co-op exploring all the false neutrals in the gears so I am well aware that it's wrong.
Helium, because I'm worth it.
Waterboarding at Guantanamo Bay sounded like a radical holiday opportunity until I looked it up.
"Rule of thumb" method to achieve same is to place heel on pedal and lock your knee straight, with the pedal at the bottom of the stroke, then set the saddle accordingly. Once you put the ball of your foot back on the pedal, the fit should be as Doomanic describes above.
DISCLAIMER: If you don't understand this shit, ask a grown up, preferably someone with deep pockets, who your widow/kids can sue. Don't trust people on the internet with your life, your credit card details or your naked selfies! This advice may contain, or indeed be written by someone who is (clinically), nuts.
What the 3 posters above me said...