Calgary businessman Brent King is driving a donated RV across Canada to drop off donations of men's underwear to homeless shelters. (David Bell)

A Calgary businessman's desire to make a small gesture to help a local homeless shelter supply a basic clothing item to its clients has turned into a cross-country road trip for charity.

It began when Brent King, 40, called the Mustard Seed Street Ministry asking what he could do to help.

"I said, 'Look, I'm interested in making a charitable donation of some description. And I'd really like to take a problem that you have and potentially try to solve it, something small, something manageable, something contained'," he told CBC News on Friday.

The charity that helps homeless people in Calgary pointed him to their wish list, at the top of which was men's underwear.

"It has to be new, and a lot of people don't think about it when they're making donations," explained King, who owns a medical devices company.

In pursuit of 2,500 pairs of men's underwear to supply the shelter for a year, King called a friend in the import business in Vancouver — who promised to help if King did the same thing for a shelter in his west coast city.

King canvassed his friends, business colleagues and sponsors and is now heading to 10 major Canadian cities in a donated RV loaded with 25,000 pairs of men's underwear imported from a manufacturer in China.

King plans to drop off 2,500 pairs at a homeless shelter in each location. He was at the Mustard Seed's Foothills location on Friday, donating enough men's underwear to last the organization a year.