Free Rule of Three Calculator
Free rule of three / cross multiplication calculator. Find the missing fourth proportional.
What does this tool do? Solve proportions easily. If A is to B as C is to X, this tool finds X for you. Great for recipes, scaling, unit conversions, and everyday math shortcuts.
Calculated entirely in your browser
View Technical Specifications (For Developers)
- Formula:
X = (B × C) / Awith division-by-zero protection - Supports: Direct and inverse proportions
If A is to B, then C is to X. Enter A, B, and C to find X.
—
Fuel the Project
Free tools, zero server uploads, total privacy.