Missing Ratio Value Calculator
Find D in A:B = C:D from three nonzero terms.
How to use Missing Ratio Value Calculator
1. Enter A, B, C in the stated order. 2. Follow nonzero denominator and whole-number requirements where they apply. Keep corresponding quantities on the same unit scale. 3. Select Calculate or press Enter to see missing d in a:b = c:d. 4. Copy result copies the output; Reset clears the inputs and answer.
Why use this tool?
Scale a defined ratio when the corresponding first term changes and the matching second term is missing.
How the calculation works
D = B × C ÷ A. A must be nonzero to determine D; B and C must also be nonzero so both quotient ratios are defined. Numeric outputs use browser floating-point arithmetic, with six decimal places at most. Smaller nonzero outputs use six significant digits in scientific notation. Unrepresentable intermediate values or numeric outputs beyond the supported magnitude are rejected. Numeric input magnitudes, including each fraction or ratio component, must not exceed 9,007,199,254,740,991. Mathematical references: https://openstax.org/books/prealgebra-2e/pages/4-key-concepts and https://openstax.org/books/prealgebra-2e/pages/6-5-solve-proportions-and-their-applications.
Example
A = 2, B = 3 and C = 10 give D = 3 × 10 ÷ 2 = 15, so 2:3 = 10:15.
Practical tip
Keep corresponding terms in matching positions. This tool finds the fourth term, not a sum-to-total split.
Frequently asked questions
Why are zero terms rejected?
A zero first term may not determine a unique fourth term, and a zero denominator gives an undefined quotient. This tool solves the nonzero proportion A/B = C/D.
Do signed inputs always have a practical interpretation?
These forms perform the stated arithmetic. Negative values, rates above 100% or a negative baseline can be mathematically valid while being unsuitable for a particular real-world quantity. Check the task and model before applying the result.
Does the tool choose units or round my input first?
Enter corresponding measurements in matching units; the maths forms do not convert units automatically. Exact fraction and ratio text is kept for integer arithmetic. Other numeric operations use browser floating-point values and the display precision stated above.