Cross Multiplication Calculator
Use this professional cross multiplication calculator to solve missing values in proportions, compare two ratios, and understand every step of the calculation clearly.
Calculate Cross Multiplication
Enter values in the form a / b = c / d. Leave one box empty to find the missing value, or fill all four boxes to check whether the proportion is true.
What Is Cross Multiplication?
Cross multiplication is a simple method used to solve proportions. A proportion compares two ratios, such as a / b = c / d. Instead of dividing each side, cross multiplication multiplies the numerator of one fraction by the denominator of the other fraction.
This method is commonly used in school math, ratio problems, recipe conversions, map scales, unit pricing, percentage problems, and real-world comparison questions.
How This Cross Multiplication Tool Works
1. Enter Your Values
Add your numbers into the proportion format. You can enter all four values or leave one value empty.
2. Apply the Formula
The calculator uses the rule a × d = b × c to compare or solve the proportion.
3. Get the Answer
You receive the final result with clear calculation steps, making it easy to understand.
When Should You Use Cross Multiplication?
Cross multiplication is useful whenever two fractions or ratios are equal and one value is unknown. It saves time and gives a clear way to solve proportion-based questions.
- Solving ratio and proportion problems
- Finding missing numbers in fractions
- Checking whether two ratios are equal
- Working with scale drawings and maps
- Converting recipe measurements
- Comparing prices, speeds, or quantities
Cross Multiplication Example
Suppose you want to solve:
Cross multiply:
So, 60 = 4x. Divide both sides by 4:
FAQs About Cross Multiplication
What is cross multiplication?
Cross multiplication is a method for solving proportions by multiplying diagonally across two fractions. For example, in a / b = c / d, you multiply a × d and b × c.
Can this calculator find a missing value?
Yes. Leave one input box empty, enter the other three values, and the tool will solve the missing number.
Can I check if two ratios are equal?
Yes. Fill in all four values and the calculator will compare the cross products to tell you if the proportion is true or false.
Why can the denominator not be zero?
A denominator cannot be zero because division by zero is undefined in mathematics.
Is cross multiplication only for fractions?
Cross multiplication is mostly used with fractions, ratios, and proportions, but it also appears in unit conversions, percentage problems, and comparison-based calculations.