Ratio Calculator
Solve mathematical proportions and missing term equations A : B = C : D using cross-multiplication. Useful for recipe scaling, screen resolutions, architectural drafting, and chemistry dilutions.
First term of reference ratio
Second term of reference ratio
First term of target proportional ratio
Value satisfying A / B = C / D (D = B × C / A)
How to Use This Calculator
- Enter the known reference ratio terms A and B.
- Enter the target term C.
- View the computed term D and simplified ratio immediately.
Formula & Calculation Methodology
Cross-multiplication equates the product of the extremes (A × D) with the product of the means (B × C), isolating the missing variable D.
Worked Example
Solving 4 : 6 = 10 : D
Aspect ratio 16 : 9 scaled to width 1920
Frequently Asked Questions
How does cross-multiplication work?↓
When two fractions are equal (A/B = C/D), multiplying both sides by (B × D) cancels the denominators, yielding the fundamental equality A × D = B × C.
Can decimals be entered as ratio terms?↓
Yes. The solver handles decimal floats, scaling them with floating-point precision.
What occurs if term A is zero?↓
Division by zero is undefined. The calculator guards against this by defaulting term A to 1.
What is a limitation of simple ratios?↓
Standard proportions assume direct linearity. In inverse proportions (e.g. more workers take less time), A × B = C × D applies instead.
Related Calculators
Source Citation & Disclaimer
Informational tool only; not licensed tax, legal, or financial advice.