What size frame bike is perfect for someone who is 5.4?

If a mountain bike is what you're after then the wheels will be 26" and the frame should be about 16". Should be able to straddle the top tube and have 2 or 3" clearance. For a road bike then the wheels will be 700C and frame 18" with 1 to 2" clearance from top tube when standing over it.

Go to a shop and they will size you because it can vary if you have long or short legs for your height.

It will also depended the bike that you are buying. The size you need on one bike might be to big on another. The bike I had in 2004 was a 17" frame (considered a medium). My 2006 bike (same bike, newer year) had a slight frame design change and it was a 15.5" frame (considered a medium).

So the kind of bike you want to ride and different manufactures will be different. So I would find a respectable bike shop and get sized for the bike you want.

Good Luck in your search.

20" sounds like a good starting point. But be advised that one makers 20" might be different form another makers version. So, you will need to try them out before buying. The word "medium" in frame sizes could mean just about anything. Again, try the bike out before buying it.

go to your local bike shop and get fitted

it is worth the extra time and effort

I'm 5'4" I ride a 26" bike, just depends on how you like to ride. I hate it when I can't straighten out my legs when I pedal.

a trike should do