Short tons (ST) and long tons (LT) are common maritime measures in the U.S., and metric tons (MT), often spelled tonnes, are used elsewhere. All are measures of weight. A short ton, used ashore and for Great Lakes vessels, is 2,000 pounds. Long tons are the preferred measure for American seagoing ships, and are 2,240 pounds, about the weight of a tun of wine. Metric tonnes, at 2,205 pounds, are also in this range, but it's coincidental. The weight of a metric tonne is based not on a tun of wine, but on the weight of one cubic meter or one thousand liters of fresh water. Oddly enough, this is 264 gallons, just a little larger than a tun, so the name stuck for the metric system, too.