Proportion Calculator
Ratios That Stay Equal
When two ratios stay equal, they form a proportion. This calculator checks the equality and solves the missing term across the two pairs. Map readers scaling distances and cooks scaling recipes lean on it constantly.
Cross Multiplication at Work
Write the proportion as a/b = c/d. Cross multiplication states that a x d = b x c, and from that product any single unknown term can be isolated.
Example: solve 2/3 = x/12 by cross multiplying to get 2 x 12 = 3x, so x = 8. Checking confirms it, since 8/12 also reduces to 2/3.
Everyday shopping makes the same math useful. If 5 kilograms of rice costs 12 dollars and you want the price of 8 kilograms, write 5/12 = 8/x, cross multiply, and x equals 96/5, or 19.20 dollars. Percent questions fit the same mold: 30 over 100 equals 27 over x solves to 90. Whenever values rise together or fall together, a proportion is the right model, and the calculator checks your setup in one press.
Entering the Two Proportions
Enter the first ratio in Proportion 1 and the second in Proportion 2, then press Calculate. Leave the unknown term blank and the tool supplies it.
Keep quantities aligned: 3 apples per 4 dollars must map to apples and dollars in the same positions of the second ratio. Never flip one side.
Frequently Asked Questions
What makes two ratios proportional?
Their cross products must match: a/b = c/d holds exactly when a x d equals b x c. Both ratios also reduce to the same simplest form.
How do I solve for x?
Cross multiply the two ratios, then divide to isolate x. In 2/3 = x/12, computing 2 x 12 divided by 3 gives x = 8. It takes one multiplication and one division.
Does entry order matter?
Yes, matching positions must hold the same quantity type in both ratios. Swapping a numerator with its denominator flips the relation and breaks the comparison. Keep units in the same slots.
What is a real world use?
If a car covers 150 kilometers in 2 hours, the proportion 150/2 = d/5 predicts the distance in 5 hours. Cross multiplying gives d = 375 kilometers.
Are decimals and fractions both accepted?
Both are supported, such as 0.5/1 matched with 2.5/5. Notation never changes the underlying ratio, so the solved value stays consistent either way. Mixed styles work in one pair.