It's back-to-school season and time for students to carry that weight.
But too much weight in kids' backpacks can cause back injuries that could last for years.
Students at Coastal Carolina University may look young and healthy, but a surprising number of them say their backpacks are a real pain.
"If you were a girl, this (backpack) would be really heavy. I don't really see how they'd be able to carry this," said freshman Akeem King.
"With the amount of textbooks we have, and if it's not a good quality (backpack), it probably does cause strain," added senior Laurel Nusbaumer.
Conway chiropractor Dr. Daniel Falk says students of all ages who carry overly-heavy backpacks can develop curvature of the spine, or middle back problems.
"And the nerves in the middle back control the lungs and we see kids who have asthma because of this, where their head's going forward and they get headaches and neck problems," said Falk.
Falk says roller bags are better than backpacks, if schools allow them.
He says he's seen kids trying to carry backpacks that weigh as much as half of the child's weight.
"Fifteen percent of body weight is probably the max of what you want to do," he said.
Falk says parents should often check out the weight of their kids' backpacks.
"If it's heavy for you to pick it up, imagine what your child's trying to do."
Also, when parents shop for a backpack, he says they should pick the right one.
"If you can get one that has a waistband strap, definitely better. But really encourage them to put it on both shoulders," said Falk.
Falk says he's done free screening for scoliosis, or curvature of the spine, at a couple of Horry County middle schools and he'd like to get more schools involved.
The U.S. Consumer Product Safety Commission says backpack-related injuries send about 5,000 children a year to emergency rooms.