Between estimating the number of freshmen who will accept offers to Virginia Tech, the number of returning students who will stay on campus and the number of those students who will change their minds during the summer, Ed Spencer has to do a lot of educated guessing in his position as associate vice president for student affairs.

But some of the math isn't so fuzzy.

For instance, 9,325 students minus 9,100 beds equals 225 unhappy students living in overbooked residence halls at Virginia Tech.

Like airlines that overbook seats, colleges overbook their residence halls every year in anticipation of no-shows. But Spencer said Tech is ideally about 50 to 100 students over occupancy when the school year begins. The situation is usually taken care of as students leave school for various reasons during the fall semester.

Spencer is confident the 225 number will shrink by the first day of class, Aug. 21. And to help it along, Tech is offering to let students out of their housing contracts and give those students $100 to spend at university dining halls.

The offer was made to returning students last week and was extended to all on-campus students on Tuesday. This is the first time since 2001 that the university has made that offer. They were overbooked by about 300 students then, but it turned out fine, Spencer said.

"Overextended housing is as common at every campus and university as students showing up in the fall," Tech spokesman Mark Owczarski said.

Spencer said there's an ebb and flow to the number of students who want to live on campus.

He attributes this year's issues to a low number of students cancelling their plans to enroll and a slightly larger number of new students than years past. He also thinks gasoline prices might be a reason more students want to live on campus.

Tech plans to open a new residence hall in 2009 that would house 256 students.

But for the time being, overflow students will be accommodated by converting student lounges into residence rooms and sharing rooms with resident advisers, who typically live alone.

Spencer said RAs are often good roommates for freshmen getting to know the school and said in the past students have enjoyed the space of the converted lounges so much that they don't want to leave for a regular room.

All things being equal, Spencer said he'd rather have too many students than too few. Booking right up to capacity helps keep room and board fees down.

"You multiply $2,578 by 225 and you've got a lot of missing income," he said.

Doug Howell, associate director of housing at Longwood University, echoed Spencer's sentiment.

Longwood is currently at about 110 percent capacity. Howell expects that to fall quite a bit as students finish summer school and academic problems weed out some of the student body.

"We need to maintain a glass that is always full. The overspill at the beginning, it will subside," Howell said. "I think any institution would be definitely in favor of a full house."

Roanoke College spokeswoman Teresa Gereaux said students are required to live on campus unless they are from the region or receive special permission.

The college uses a lottery to allow students to live off campus if there isn't enough residence space.

That took care of the overflow problem this year.

Of the approximately 1,900 students at Roanoke College, 1,231 are living on campus this year. New residence halls have added 200 beds to campus over the past two years.

The problems with carbon monoxide poisoning in a residence hall last month have not affected the college's housing capacity, she said.

Radford University is putting its extra on-campus students into double rooms converted to house three students.

By the second week of the year, most if not all of the 122 "triples" should be back to doubles, spokesman Rob Tucker said.