Proportion Calculator
Solve A:B = C:D. Leave exactly one field blank, then calculate the missing value using cross multiplication.
A : B = C : D
Privacy: calculations run locally in your browser. No inputs are stored or transmitted.
How it works
Cross multiplication: A:B = C:D ⇒ A×D = B×C
Solve the missing term by rearranging:
- If A is missing: A = (B×C) ÷ D
- If B is missing: B = (A×D) ÷ C
- If C is missing: C = (A×D) ÷ B
- If D is missing: D = (B×C) ÷ A
Examples
- 2:3 = 10:D → D = 15
- A:8 = 3:12 → A = 2
- 5:B = 20:4 → B = 1
When to use this tool
This tool is designed for quick, practical tasks such as everyday calculations, data formatting, or simple conversions. It is best used when you need fast results without installing software or using complex tools.
When to use
- Quick checks or one-time calculations
- Validating or converting data before using it elsewhere
- Simple tasks that do not require advanced software
When not to use
- Critical financial, legal, or medical decisions
- Large-scale or automated processing
- Situations requiring guaranteed precision beyond basic validation
Always review results before using them in important contexts.
About this tool
This tool helps you perform quick utility operations directly in your browser. It runs entirely in your browser without sending data to a server.
You can use this tool when handling simple tasks without installing additional software. The results should be interpreted as a processed output based on your input data.
FAQ
- What is a proportion?
A proportion states that two ratios are equal, written as A:B = C:D.
- How do you solve a proportion?
Use cross multiplication: A×D = B×C. If one value is missing, rearrange to solve for it.
- How many blanks can I leave?
Leave exactly one field blank. If more than one is blank, the problem is underdetermined.
- Can I use decimals and negative numbers?
Yes. Decimals and negatives are supported. Negative values can represent directional changes or signed quantities.
- What if a divisor would be 0?
Some cases are undefined (division by zero). The tool will warn you if the missing value cannot be solved with the given inputs.
- Is this the same as percentage?
Not always. Proportions compare ratios. Percent is a ratio out of 100. You can convert a proportion to percent in some cases (e.g., part/whole).