What is a Simple Ratio Calculator?
This calculator solves proportions of the form A:B = C:X for an unknown value.
How it's calculated
A:B = C:X → X = B×C÷A, using the property that the product of the means equals the product of the extremes.
Proportions are about scaling while keeping the ratio fixed
Proportions come up almost exclusively when you need to change scale while keeping the underlying relationship the same — scaling a recipe from 4 to 6 servings, converting a map scale to real-world distance, or converting a per-unit price to a different quantity. The ratio stays fixed; only the size changes. That's the entire idea behind proportional reasoning.
Good to know
- Unit pricing (price per 100g) on store shelves exists precisely so shoppers can compare products of different sizes on the same basis — required by regulation in many places because larger packages aren't always cheaper per unit.
- The golden ratio (about 1:1.618) is frequently cited in art and architecture, but many of the most famous claimed examples are disputed as retroactive pattern-matching rather than intentional design.
- Standard paper's 1:√2 ratio is far more practically useful — folding it in half preserves the exact same ratio, which is why paper sizes scale cleanly into each other.
- A map scale of 1:25,000 means 1cm on the map represents 250m in reality.
- Recipes generally scale reliably at any multiple, but leavening agents like salt or baking soda are often kept slightly below strict proportion for best results.
Frequently asked questions
Q. What's the difference between a ratio and a proportion?
A ratio compares two quantities (3:2); a proportion expresses relative size against a reference (1.5, or 150%).
Q. How do I scale a recipe up by 1.5x?
Multiply every ingredient by 1.5, though leavening agents are often kept slightly below strict proportion.
Q. Which shows more detail, a 1:100 or 1:50 scale drawing?
1:50 — the same object is drawn larger, showing finer detail.