Science, Tech, Math › Science What Is an Exact Number? Share Flipboard Email Print ballyscanlon / Getty Images Science Chemistry Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated July 09, 2019 An exact number is a value that is known with complete certainty. Examples of exact numbers are counted numbers of objects or certain unit conversions. For example, there are exactly 3 feet in 1 yard. There are exactly 12 eggs in a dozen. A class may contain exactly 25 students. Most exact numbers are integers, but it's possible for a value to have a decimal point. An exact number cannot be simplified or reduced. Examples of Exact Numbers For example, these are exact numbers: Number of ounces in a poundNumber of feet in a mileNumber of centimeters in a meterAny counted number, such as the number of apples in a bag Exact Numbers and Uncertainty An exact number is considered to have an infinite number of significant figures. It does not limit the number of significant figures in a calculation. It does not contribute to uncertainty in a calculation. While counted numbers are exact, any measured value contains inherent uncertainty. The uncertainty comes from the limit of the measuring device and the skill of the person performing the measurement.