Shoe sizes are measured similarly in the United Kingdom and the United States. U.S. shoe sizes are typically one number larger than the U.K. sizes, since U.S. sizes start at one and U.K. sizes start at zero. The methods for determining the sizes are the same.
Shoe sizes in both the United Kingdom and the United States are measured using a last. The last is shaped like the human foot, and the material is stretched over it during the making of the shoe. Each shoe size uses a different size last. This ensures that the shoes are uniform size, but does not guarantee that shoe size translates from one manufacturer to another.