Things You'll Need:
- ruler
- object to be measured
- paper and pencil, optional
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Step 1
Use a foot/inch ruler to calculate fractions in 8ths or 16ths. The longest, numbered vertical lines on the ruler measure length in inches. The next-longest line, equidistant between two numbered lines, marks a half-inch (the line equidistant between 2 and 3 marks 2 1/2). The next longest lines mark quarter inches (since 2/4 = 1/2, the 1/2-inch line stands for both). Customarily, the very shortest vertical lines on a ruler stand for 1/8-inch measurement (2/8 = 1/4, 4/8 = 1/2). On some rulers, even smaller lines will mark an inch in 1/16 intervals, although rulers marked this finely are seldom available for ordinary household use. If you need to measure something in 16ths, use a pencil to place a dot between the correct 8th markings. A measurement of 9/16, for example, requires a dot between the 1/2 mark (8/16) and the next following 1/8 line (10/16).
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Step 2
Use a metric ruler to measure centimeters and millimeters. Because the metric system is decimal-based, each centimeter is divided into 10 millimeter sections. The longest vertical line equidistant between two numbered lines stands for 1/2, or 5 millimeters. Fractions are usually expressed in decimal form: 4.2 (4 and 2/10) centimeters, for example. A ruler long enough to measure a full meter will have 100 numbered centimeters, allowing you to measure, for example, 37.5 centimeters. Although it is mathematically valid, it would be unusual to describe your measurement as 1/4 or 1/8 meter.
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Step 3
Use a ruler with both inch and metric markings as an easy way to convert one measurement to the other. It is useful for planning, for instance, to know that 2.5 centimeters are very close to 1 inch. Especially if you are trying to order fabric, clothing, model parts or hardware from a company outside the US, measurements may be exclusively in meters. A ruler showing both measuring systems will help you determine approximate equivalent sizes for what you are ordering.
