Students assigned to Yale’s 13th and 14th residential colleges won’t be lonely in their perch at the base of Science Hill.

For one thing, they will certainly not lack company. While administrators have not said so publicly, the two new colleges will have more beds than any of the existing colleges, according to housing data obtained by the News. The colleges will be so epic, in fact, that each will house roughly as many students as Trumbull and Jonathan Edwards colleges put together — about 425, according to an analysis of the housing data, which was provided to the News by the Yale College Dean’s Office.

The relative size of the new colleges may come as a surprise to many students and faculty members, as the expansion plan pitched by administrators last year — and studied for months by two faculty committees — did not call for quite so large an increase in undergraduate enrollment. It also could reignite questions about whether the new colleges will damage Yale College’s treasured intimacy, a chief worry among students who opposed expansion last year.

At that time, administrators proposed expanding the College by about 12 to 13 percent, from 5,300 students to 5,950 or 6,000.

But when University President Richard Levin announced to the community in June that the Yale Corporation, the University’s highest governing body, had officially authorized the expansion he said Yale’s undergraduate enrollment would grow “by about 15 percent,” or an increase of about 800 students.

Was Levin’s description — echoed by materials distributed by the Office of Public Affairs and Office of Development — merely an approximation, a shift to a rounder number that might roll off the tongue smoother on the 6 o’clock news?

No, it turns out. “We took the numbers up a little bit,” Levin told the News. “The Corporation said, ‘Why do these colleges have to be [medium-sized]? … What if they’re as large as some of the largest colleges?’ ”

And after all, the entire goal of expansion is to “make an even greater contribution to society by preparing a larger number of talented and promising students of all backgrounds for leadership and service,” as the president put it when the Corporation authorized the expansion. So, he said, why not squeeze in a few more?

The new colleges are now projected to house 425 students each, University Planner Laura Cruickshank confirmed Thursday.

That makes the new colleges the largest of all, even when compared to the two other colleges, Silliman and Timothy Dwight colleges, that house their freshmen in the college, as the new colleges will do. As of last fall, when statistics were last available, the capacities of the existing 12 colleges ranged from a low of 211 students in Trumbull and JE to a high of 402 students in Silliman.

Of course, judging the size of the new colleges depends on the metric used. By square footage, each new college — at 220,000 square feet — will be about 15 percent smaller than Silliman. And the overall size of their communities, counting students affiliated with them but not necessarily living there, will not actually be much larger than many of those now at the existing 12 colleges.

While predicting the rate at which upperclassmen in a certain college in a certain year will choose to live off campus is almost impossible, in general, about 12 to 13 of every 100 Yale College students choose to live off campus in a given year, according to data from the Office of Institutional Research. That would suggest as many as 480 students could be affiliated with each of the new colleges.

By contrast, Pierson College last year had 485 affiliated students, followed by Saybrook College at 477, Branford College at 458 and Morse College at 448. Those numbers, however, may shrink slightly; as part of the expansion plan, the University plans to reduce the population assigned to the existing 12 colleges by about 140 students in order to largely eliminate annexing.

The yet-unnamed new colleges, to be designed by School of Architecture Dean Robert A.M. Stern ARC ’65, are slated to open in the autumn of 2013. Construction on the $600 million project will begin in 2011.