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Solve proportions and find missing ratio values.
⚖️ Solves proportions. Example: 3/4 = 9/D → D = 12. Useful for recipes, scaling, and maps.
A ratio compares two quantities, like 3:2 or 5 to 4. This calculator solves proportions — given three values of A:B = C:D, it finds the fourth. It also simplifies ratios to lowest terms.
In a proportion A:B = C:D, the cross products are equal: A × D = B × C. So if you know any three values, you can solve for the fourth. To find D: D = (B × C) ÷ A.
A recipe serves 4 and uses 2 cups of flour. How much flour for 6 servings? Set up the proportion 4:2 = 6:D. Solving: D = (2 × 6) ÷ 4 = 3 cups.
The Ratio Calculator lets you figure out ratio calculatorinstantly, without reaching for a spreadsheet or doing the math by hand. Whether you're planning a budget, checking a loan, or working through homework, the tool applies the correct formula behind the scenes and shows the result the moment you enter your numbers.
Unlike a static chart or table, this calculator adapts to your exact inputs. You can adjust any value and see the outcome update in real time, which makes it easy to compare scenarios — for example, "what if the rate were 1% lower?" or "what if I paid an extra $50 a month?"
Common uses: people reach for this tool when they need to find a ratio calculator solve proportion, find missing value in ratio, cross multiply proportion solver, or solve proportion a b c d.
Browser-based tools like this one have a few real advantages over installed software or manual methods:
The Ratio Calculator is based on the following formula:
a : b = (a/g) : (b/g), g = GCD(a, b)
Variables: a, b = The two terms of the ratio g = GCD(a, b), the largest number dividing both terms
Simplify a ratio by dividing both terms by their greatest common divisor. Scaling multiplies both terms by the same factor so the proportion is preserved.
Worked example: Step 1: Simplify 36 : 60. Step 2: GCD(36, 60) = 12. Step 3: 36 / 12 = 3 and 60 / 12 = 5. Result: 36 : 60 = 3 : 5.
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