No cans currently in wide use are composed primarily or wholly of tin; that term rather reflects the nearly exclusive use in cans[clarification needed], until the second half of the 20th century, of tinplate steel, which combined the physical strength and relatively low price of steel with the corrosion resistance of tin. Depending on contents and available coatings, some canneries still use tin-free steel.
In some local dialects, any metal can, even aluminium, might be called a "tin can". Use of aluminium in cans began in 1957. Aluminium is less costly than tin-plated steel but offers the same resistance to corrosion in addition to greater malleability, resulting in ease of manufacture; this gave rise to the two-piece can, where all but the top of the can is simply stamped out of a single piece of aluminium, rather than laboriously constructed from three pieces of steel.
A can traditionally has a printed paper or plastic label glued to the outside of the curved surface, indicating its contents. Some labels contain additional information, such as recipes, on the reverse side. Recently labels are more often printed directly onto the metal before or after the metal sheet is formed into the individual cans.
In November 1991 US can manufacturers voluntarily eliminated lead seams in food cans. However, imported food cans continued to include lead soldered seams. In 1995 the US FDA issued a rule prohibiting lead soldered food cans, including both domestic and imported food cans.
In modern times, the majority of food cans in the UK have been lined with a plastic coating containing bisphenol A (BPA). The coating prevents acids and other substances from corroding the tin or aluminium of the can, but leaching of BPA into the can's contents is currently (as of 2013) being investigated as a potential health hazard.
Cans come in a variety of shapes: two common ones are the "soup tin" and the "tuna tin". Walls are often stiffened with rib bulges, especially on larger cans, to help the can resist dents that can cause seams to split.
Can sizes in the United States have an assortment of designations and sizes. For example, size 7/8 contains one serving of half a cup with an estimated weight of 4 ounces; size 1 "picnic" has two or three servings totalling one and a quarter cups with an estimated weight of 10½ ounces; size 303 has four servings totalling 2 cups weighing 15½ ounces; and size 10 cans, most widely used by food services selling to cafeterias and restaurants, have twenty-five servings totalling 13 cups with an estimated weight of 103½ ounces (size of a roughly 3 pound coffee can). These are U.S. customary cups (not British Imperial standard).
In the United States, cook books sometimes reference cans by size. The Can Manufacturers Institute defines these sizes, expressing them in three-digit numbers, as measured in whole and sixteenths of an inch for the container's nominal outside dimensions: a 307 x 512 would thus measure 3 and 7/16" in diameter by 5 and 3/4" (12/16") in height. Older can numbers are often expressed as single digits, their contents being calculated for room-temperature water as approximately eleven ounces (#1 "picnic" can), twenty ounces (#2), thirty-two ounces (#3) fifty-eight ounces (#5) and one-hundred-ten ounces (#10 "coffee" can).
In parts of the world using the metric system, tins are made in 250, 500, 750 mL (millilitre) and 1 L (litre) sizes (250 mL is approximately 1 cup or 8 ounces). Cans imported from the USA often have odd sizes such as 3.8 L (1 US gallon), 1.9 L (1/2 US gallon), and 946 mL (2 US pints / 1 quart).
In the UK and Australia, cans are usually measured by net weight. A standard size tin can holds roughly 400 g; the weight can vary between 385 g and 425 g, depending on the density of the contents. The smaller half sized can holds roughly 200 g, and it can vary between 170 g and 225 g.