Size up if the recipient prefers a relaxed fit, is between sizes, or you're buying cotton that might shrink. Size down only if they like a slim, tailored look and the chart measurements are already generous. Stick with the chart if the measurements match a tee they already wear comfortably.

For a gift, the default should be size up. It's the safer choice. A slightly big tee is easier to live with than a slightly small one. And if it's too big, you can always exchange.