Proportion Calculator
Proportion Calculator solves A:B = C:X with X = B×C÷A. It is mathematically the same direct-proportion structure as the rule of three, presented with explicit A, B, and C labels. Correct correspondence and a nonzero A are essential; the calculator does not detect whether the real-world relationship is actually proportional.
Runs locally — files stay on your deviceHow do I solve 2:3 = 8:X?
X equals 12.
Formula: X = 3 × 8 ÷ 2 = 12
A proportion states that two ratios are equal
A/B = C/X leads to A×X = B×C. Dividing both sides by nonzero A gives X = B×C/A.
How it works
Enter corresponding values into A, B, and C, then verify the solved ratio by comparing A/B with C/X.
Key concepts
Cross-products are equal
For a true proportion, A×X and B×C match.
Equivalent ratios share a scale factor
Moving from A to C uses the same factor as moving from B to X.
When to use it
- Solve one unknown in an equivalent ratio.
- Scale a directly proportional quantity.
- Check cross-multiplication.
When not to use it
- Do not model an inverse or nonlinear relationship.
- Do not use zero for A.
- Do not treat correlation as proof of proportionality.
Worked examples
Equivalent ratio
- Input
A=2, B=3, C=8- Expected output
X=12
Both ratios equal two thirds.
Decimal scale
- Input
A=0.5, B=2, C=3- Expected output
X=12
The algebra works with finite decimals.
Zero A
- Input
A=0, B=2, C=3- Expected output
Undefined formula
The solution requires division by A.
Common mistakes
Swapping B and C
Corresponding terms no longer align. Correction: Write the relationship before entering values.
Using an additive pattern
Proportions preserve multiplication, not fixed differences. Correction: Check a common scale factor.
Skipping verification
A data-entry error can look plausible. Correction: Compare the two resulting quotients.
Best practices
- Label corresponding quantities.
- Estimate the scale factor.
- Verify both ratios afterward.
Related operations and differences
Ratio Calculator
Choose Ratio Calculator when you need to calculate the ratio between two numbers.; use Proportion Calculator specifically for proportion.
Rule of Three Calculator
Choose Rule of Three Calculator when you need to solve direct proportions with one unknown value.; use Proportion Calculator specifically for proportion.
Average Calculator
Choose Average Calculator when you need to find the arithmetic mean of a number list.; use Proportion Calculator specifically for proportion.
Fraction to Decimal
Choose Fraction to Decimal when you need to convert a numerator and denominator to decimal.; use Proportion Calculator specifically for proportion.
Percentage Difference Calculator
Choose Percentage Difference Calculator when you need to compare two values by their average magnitude.; use Proportion Calculator specifically for proportion.
Weighted Average Calculator
Choose Weighted Average Calculator when you need to calculate an average using matching weights.; use Proportion Calculator specifically for proportion.
Limitations and privacy
- Only direct proportion is solved.
- A must be nonzero.
- Units and real-world proportionality are not inferred.
Numbers and results remain in this browser.
Frequently asked questions
What is the proportion formula?
X = B×C÷A.
Is this the rule of three?
Yes, it is the same direct-proportion algebra.
Why must A be nonzero?
The solution divides by A.
How can I check the result?
Verify that A/B equals C/X where the denominators are nonzero.