Many Americans know they’ve put on weight during the pandemic, but it’s been difficult for experts to detail the scope of the problem.

Soon after the pandemic started over a year ago, Americans started joking about the dreaded “quarantine 15,” worried they might gain weight while shut in homes with stockpiles of food, glued to computer screens and binge-watching Netflix.

The concern is real, but assessing the problem’s scope has been a challenge. Surveys that simply ask people about their weight are notoriously unreliable, and many medical visits have been virtual.

Now a very small study using objective measures — weight measurements from Bluetooth-connected smart scales — suggests that adults under shelter-in-place orders gained more than half a pound every 10 days.

That translates to nearly two pounds a month, said Dr. Gregory M. Marcus, senior author of the research letter, published on Monday in the peer-reviewed JAMA Network Open. Americans who kept up their lockdown habits could easily have gained 20 pounds over the course of a year, he added.