Two decades after Congress called for educational programmes and voluntary conversion, virtually everyone still uses inches, pounds and gallons.
"In the metric system," asked the woman, "how old would I be?" Ignorance of millimetres, deci-litres and hectograms persists in the United States, the only nation on the planet save Liberia and Burma that has yet to go metric.
Congress passed the Metric Conversion Act 20 years ago this December, but the measure made conversion voluntary.
Most Americans, including educators, have ignored it. "You can teach it but if people don't have any need to use it, they won't learn it. That's the problem, " said Ann Loew, director of the American National Metric Council.
A national pro-metric group of engineers and academics estimates that barely 10 percent of schools teach metric, most of them only after students master customary US measurements. Like other metric advocates, they want both systems to be taught concurrently.
"So many people say they'll get mixed up," said Valerie Antoine, a California engineer and president of the group, the US Metric Association.
"Well, they're learning foreign languages and they're not getting mixed up about English."
Lockheed, Caterpillar and other US-based global corporations now require that employees know the metric system. Such companies are forced to teach their workers on the job and are now pushing for the schools to do more.
There has been some progress. As of this year, anything sold to or regulated by the federal government - including construction plans for roads and buildings - must be metric.
The automotive industry, farm-equipment manufacturers and makers of scientific and medical equipment use the metric system. And an occasional highway distance sign appears both in miles and kilometres.
Yet officials at the Department of Education, which is required to compile annual reports on metric conversion activities, couldn't find one more recent than 1992. Two pages long, it pointed out that the department "is not authorised to require metric education".