Science, Tech, Math › Science Direct Proportion Definition Share Flipboard Email Print Science Chemistry Chemical Laws Basics 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 September 11, 2018 Definition: Direct proportion is the relationship between two variables when their ratio is equal to a constant value. Examples: The volume of an ideal gas is directly proportional to the absolute temperature of the gas (Charles' Law)If you get paid by the hour, the more you work the more you will get paid. If you earn $15/hour and work 2 hours, you will earn $30 (Not including taxes, etc.) and if you work 4 hours, you will earn $60. The ratio of money earned to hours worked is 15 to 1 or $15/hour.