… make numbers easy for readers to digest. Usually, this means rounding off very large numbers if there’s not a good reason for them to be exact.
NO: On average, Earth is 92,955,807 miles (149,597,870 kilometers) from the sun.
YES: On average, Earth is about 93 million miles (150 million kilometers) from the sun.
… use precise numbers if the context requires it.
NO: The fluoride concentration in the water supply was about 4 milligrams per liter but exceeded the 4 mg/L limit set by the EPA.
YES: The fluoride concentration in the water supply was 4.023 milligrams per liter, which exceeds the 4 mg/L limit set by the EPA.
… use the unit that makes the most sense within the context.
NO: Male giraffes grow to be 216 inches (550 cm) tall.
YES: Male giraffes grow to be about 18 feet (5.5 meters) tall.
… round off arbitrarily. For example, say a study had 100,483 participants. We should not randomly choose at which point to round off the number; this is such a large number that “more than 100,000” will get the point across.
NO: Researchers studied nearly 100,500 people with diabetes.
YES: Researchers studied more than 100,000 people with diabetes.
… imply a false sense of precision. If a number is being given as an approximation, the conversion should not be an exact number, either.
NO: New York is about 3,000 miles (4,828 kilometers) from Los Angeles.
YES: New York is about 3,000 miles (5,000 kilometers) from Los Angeles.
… use “about” with precise numbers. This guideline applies even if you rounded off the number from an even more precise figure.
NO: Of the study participants who were married, about 67.3 percent had children.
YES: Of the study participants who were married, about 67 percent had children.
YES: Of the study participants who were married, 67.3 percent had children.