Doubling time is the period it takes for a quantity to double in size or value. It is commonly used in fields like population studies, finance, and biology to understand growth rates. For example, if a population of bacteria doubles every hour, its doubling time is one hour. The concept is often illustrated using the Rule of 70, which estimates doubling time by dividing 70 by the growth rate percentage. For instance, if a population grows at 5% per year, its doubling time would be approximately 14 years (70 ÷ 5 = 14). This helps in predicting future growth.