Summarize the following:
Keep your spine straight and your shoulders back. Your arms should hang loosely at your sides. Your hands and fingers should also be loose and pointing down at the floor. The term "dominant hand" refers to the hand you are most comfortable with for precision tasks. This generally equates to the hand you use to write, handle tools, or throw a ball.  In some cases, your sword hand may not be the same as the hand you use for writing or using tools. To verify your sword hand, hold a straight piece of wood or a household item. This should be roughly the length of your forearm. The hand in which this is most comfortable is your sword hand. When you spread your fingers out, the space between your thumb and forefinger will form a V-shape. With your hand still loose at your side and your fingers pointing toward the ground, use a tape measure to determine the distance between the same side eye as your dominant hand and the base of this V-shape in your dominant hand. This measurement can be difficult to take accurately without help. You may want a friend or family member to assist you in this. Generally, when you are within a ½ in (1.2 cm) of the next full inch mark, round up to the next inch. When you are over a ½ in from the next full inch, round down to the next full inch mark.  Depending on the kind of sword you are using, sizing conventions can vary. These measurements are for a modern, straight bladed military saber. Most mass produced bladed weapons, like swords, are broken down into sizes. These sizes are generally in standardized increments, like 1 or 2 inches (2.5 to 5 cm). As an example of a sword with a different size expectation, a traditional broadsword ranges from 30 to 45 inches (76.2 to 114.3 cm).

Summary:
Assume a straight-backed posture. Identify your dominant hand. Measure between the cleft of your thumb/forefinger and eye. Round up or down to the next full inch (2.5 cm).