Measurements!

My $200-bought-off-craigslist-with-little-research beater Mizutani Super Seraph has a top tube length of 55cm, but it does feel like the bars are pretty close to me.

(I bought my current bike over summer thinking I wouldn't want to spend much money on a bike for college, but I've changed my mind after investing more time in biking.)
If it helps with sizing, the bike has 170mm Sugino RT cranks.

Entered more accurate measurements into the Bike Fit Calculator, was suggested to have 55.7-56.1cm top tube. Some more details if anybody is interested

Looks like I'll be going for the 55cm then. Is anything else significant for sizing?
(The stupid part of me still has doubts since the number 55 is different than the regular 57/58cm numbers I've been reading about for people around 6')