Math calculator
Proportion Calculator
Solve proportions using cross multiplication.
About the proportion calculator
The proportion calculator solves for the unknown in a proportion using cross multiplication.
How to use this calculator
- 1
Enter three values
Enter A, B, and C to solve for D in A:B = C:D.
- 2
View results
See the solved value and the complete proportion.
How the calculation works
In a:b = c:d, solve for d using cross multiplication: d = (b × c) ÷ a.
Example: If 2:5 = 4:x, then x = 10.
When to use a calculator vs. mental math
Simple operations like percentages and proportions are great for mental math. Complex problems — quadratic equations, standard deviation, and base conversions — benefit from calculator precision. Always estimate the answer first to catch input errors, and verify results with a second method when possible.
Important limitations
This tool provides a mathematical estimate based only on the values entered. It does not account for regulations, taxes, lender fees, market conditions, or individual circumstances. Results are for planning purposes only — consult a qualified professional for regulated, medical, financial, or construction decisions.
Frequently asked questions about proportion calculator
How accurate is the proportion calculator?+
The calculation follows the displayed formula and retains full numeric precision before formatting the result.
Can I use the result professionally?+
Use it as a planning estimate. Confirm regulated, medical, financial, or construction decisions with a qualified professional.