The thickness of curtain rods refers to their diameter, the distance across the widest point. Measured in inches, curtain rod diameters can range from less than an inch up to 3 inches wide.

When the New York Times Building opened in late 2007, critics marveled at the 3-inch-diameter ceramic rods covering the façade of the 52-story skyscraper—the first glass tower with a sunscreen to be ...