Multiplying Decimals — Definition, Formula & Examples
Multiplying decimals is the process of multiplying two or more numbers that have decimal points. You multiply as if they were whole numbers, then place the decimal point in the answer by counting the total number of decimal places from all the factors.
To compute the product of two decimal numbers, multiply their absolute integer equivalents (ignoring decimal points) and then position the decimal point in the result so that the total number of digits to the right of the decimal equals the sum of the decimal places in both factors.
How It Works
First, ignore the decimal points entirely and multiply the numbers as if they were whole numbers. Next, count the total number of digits after the decimal point in each factor you started with. Finally, place the decimal point in your answer so it has that same total number of digits after the decimal point. For example, if one factor has 1 decimal place and the other has 2, your answer needs 3 decimal places.
Worked Example
Problem: Multiply 2.5 × 1.4
Step 1: Ignore the decimal points and multiply as whole numbers: 25 × 14.
Step 2: Count the total decimal places in the original factors. 2.5 has 1 decimal place and 1.4 has 1 decimal place, so the total is 2.
Step 3: Place the decimal point in 350 so there are 2 digits after it.
Answer: 2.5 × 1.4 = 3.50, which equals 3.5
Another Example
Problem: Multiply 0.06 × 0.3
Step 1: Ignore decimals and multiply as whole numbers: 6 × 3.
Step 2: Count the total decimal places. 0.06 has 2 decimal places and 0.3 has 1, so the total is 3.
Step 3: The product 18 only has two digits, so add a leading zero to make 3 decimal places: 0.018.
Answer: 0.06 × 0.3 = 0.018
Why It Matters
Multiplying decimals shows up constantly when calculating prices, measurements, and tips — for instance, finding the cost of 2.5 pounds of fruit at $1.80 per pound. It is a foundational skill in 4th and 5th grade math that you will rely on through algebra, science courses, and everyday budgeting.
Common Mistakes
Mistake: Placing the decimal point based on only one factor instead of counting decimal places from both factors.
Correction: Always add the decimal places from every factor together. If you multiply a number with 2 decimal places by one with 1 decimal place, the product needs 3 decimal places.
Mistake: Forgetting to add leading zeros when the product has fewer digits than the required decimal places.
Correction: If you need 3 decimal places but your whole-number product is only 18 (two digits), pad with a zero on the left to get 0.018.