Rule of Three Calculator
Calculate direct proportions easily with our rule of three calculator. Perfect for price calculations, material ratios, and educational purposes.
📐 Rule of Three Formula
If a is to b, then c is to x
📝 Enter Values
Result
Fill in the values above
📈 Proportion Visualization
✨ Key Features
Everything you need for proportion calculations
Easy Calculation
Simple interface for quick rule of three calculations with instant results
Step-by-Step
Detailed calculation steps to help you understand the process
Quick Examples
Pre-loaded examples for common scenarios like pricing and ratios
Unit Support
Add units to your calculations for better context and clarity
Calculation History
Keep track of your recent calculations for easy reference
Mobile Friendly
Responsive design that works perfectly on all devices
🎯 Perfect For
Discover how different professionals use our rule of three calculator
Students & Teachers
Perfect for learning proportions, solving math homework, and understanding ratio relationships with step-by-step explanations.
Business & Retail
Calculate pricing, bulk discounts, material costs, and inventory ratios for business operations.
Engineering & Construction
Calculate material ratios, paint coverage, concrete mixtures, and construction proportions.
Cooking & Recipes
Scale recipes up or down, calculate ingredient proportions, and adjust serving sizes accurately.
❓ Frequently Asked Questions
Everything you need to know about the rule of three
What is the rule of three?
The rule of three is a mathematical method for solving proportion problems. It states that if you have three known values in a proportion, you can find the fourth unknown value using the formula: x = (b × c) / a, where a:b = c:x.
How do I use this calculator?
Simply enter three known values in the fields labeled A, B, and C. The calculator will automatically compute the fourth value (X) using the rule of three formula. You can also add units for better context, and the calculator will show step-by-step calculations.
What are some common examples?
Common examples include: Price calculations (if 4 kg costs $36, how much do 18 kg cost?), Recipe scaling (if 3 cups serve 12 people, how much for 32 people?), Material ratios (if 5 liters need 2 cans of paint, how many cans for 7 liters?).
Can I use decimal numbers?
Yes! The calculator supports decimal numbers and will provide precise results. You can enter values like 2.5, 10.75, or 0.33 for more accurate calculations.
What's the difference between direct and inverse proportion?
This calculator handles direct proportion, where both quantities increase or decrease together (like price and quantity). In inverse proportion, when one quantity increases, the other decreases (like speed and time for a fixed distance).
⭐ What Users Say
Join thousands of satisfied users who trust our rule of three calculator
"This calculator is a lifesaver for my math homework! The step-by-step explanations help me understand the process, not just get the answer."
"Perfect for my restaurant business! I use it daily to calculate ingredient proportions when scaling recipes up or down for different group sizes."
"As a contractor, I use this for material calculations all the time. The unit support makes it easy to work with different measurements. Highly recommended!"
Based on 2,156+ user reviews
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