When you multiply a number by 0.1, 0.01, or 0.001, you are making the number smaller. Each multiplication moves the digits to the right in place value — the opposite of multiplying by 10, 100, or 1,000.
Each zero in the decimal (0.1, 0.01, 0.001) moves the digits one more place to the right. Think “divide by 10” for each place value you move.
Each place to the right in a number is ten times smaller. When you multiply by 0.1, you move every digit one place to the right. When you multiply by 0.01, you move every digit two places to the right, and so on.
When you move digits to the right, the number gets smaller because you are taking parts of the whole, not adding more.
Multiplying decimals by 0.1, 0.01, or 0.001 follows the same rule as whole numbers — you still move digits to the right according to the number of zeros after the decimal point.
Check your answer by estimating. For example, 4.5 is close to 5, and 5 × 0.1 is 0.5 — so 0.45 makes sense.
We use these kinds of calculations when measuring or working with money, science, and data. Multiplying by small decimals helps describe parts of wholes, such as tenths, hundredths, or thousandths.
Understanding decimals helps you work with real-world numbers like money, measurements, and data in science and technology.