Ratio Calculator
Solve for the missing value in a proportion, simplify ratios to lowest terms, compare two ratios, scale ratios up or down, and convert ratios to fractions, decimals, and percentages. Free, private, and runs entirely in your browser.
Solve for the Missing Value
Enter three values from a proportion A : B = C : D and click Solve. Leave one field blank to find its value.
A × D = B × C. Then divide by the coefficient of the unknown.
What is a ratio?
A ratio is a way of comparing two or more quantities by division. It tells you how many times one value contains, or is contained within, another. When you write a ratio like 3 : 2, you're saying "for every 3 units of the first quantity, there are 2 units of the second."
Ratios appear everywhere: recipes (flour to sugar), maps (1 cm on the map = 1 km in real life), finance (debt-to-equity ratio), business (profit margin), and even in screen resolutions (16:9). They're one of the most practical math concepts you'll use in everyday life — which is why having a reliable ratio calculator saves so much time.
Every ratio can be written three ways: as A : B (with a colon), as a fraction A / B, or as a decimal. This calculator handles all of them, plus scales, simplifies, and compares ratios in any format.
How to use the ratio calculator
This calculator has five modes. Pick the one that matches your problem:
- Solve for X: Enter three values from a proportion
A : B = C : Dand leave one blank. The calculator finds the missing value and shows the step-by-step cross-multiplication. - Simplify: Enter any ratio (two or three terms, including decimals) and get its simplest form. The calculator finds the GCD and divides all terms by it.
- Compare: Enter two ratios and find out whether they're equivalent. You get the cross-multiplication check and the decimal comparison.
- Scale: Multiply a ratio by any factor to scale it up or down. Perfect for recipes, maps, and models.
- Convert: Turn a ratio into a fraction, decimal, percentage, simplified form, and the "A as fraction of total" value.
All results appear instantly as you type. Click any output card to copy its value to your clipboard.
Ratio formulas used by this calculator
D = (B × C) / A
12 : 18 → GCD(12, 18) = 6 → 2 : 3
Percentage = (A / B) × 100
Why use this ratio calculator?
Five tools in one
Solve proportions, simplify, compare, scale, and convert ratios — all without switching pages or opening a calculator app.
Step-by-step solutions
Every result comes with the exact math used to get there. Perfect for homework, teaching, and verifying your own work.
Handles decimals and 3-term ratios
Not just whole numbers. Enter decimals like 1.5 : 2.5 or three-term ratios like 2 : 3 : 5 — the calculator handles both.
Click-to-copy outputs
Copy any result — fraction, decimal, percentage, simplified form — with a single click.
100% private
Everything runs in your browser. No numbers are sent to any server. Close the tab and it's gone.
Works offline
Once the page loads, you can use the calculator without an internet connection. Perfect for exam prep.
Real-world uses for a ratio calculator
Cooking and baking
Recipes are ratios. If a cake recipe calls for 2 cups flour : 1 cup sugar and you want to double it, scale the ratio by 2 to get 4 : 2. If you want to halve it, scale by 0.5. The ratio calculator does this in one click.
Shopping and pricing
When comparing product sizes, the ratio of price to quantity tells you which is the better deal. If a 500 g pack costs $4.50 and a 750 g pack costs $6.75, the ratios 4.50 : 500 and 6.75 : 750 are equivalent — meaning they're priced the same per gram.
Maps and scale drawings
A map with a 1 : 50,000 scale means 1 cm on paper equals 50,000 cm (500 m) in real life. If you measure 4 cm on the map, that's 4 × 50,000 = 200,000 cm = 2 km. The scale mode handles this instantly.
Business and finance
Financial ratios like price-to-earnings (P/E), debt-to-equity, and current ratio compare two values. Understanding ratios is essential for comparing companies, analysing investment opportunities, and evaluating financial health.
Education
Ratio problems are a standard part of middle school and high school math. Whether you're solving proportions in algebra, comparing ratios in statistics, or scaling geometric figures, this calculator gives you the answer and the reasoning.
Everyday life
Mixing paint, diluting cleaning products, adjusting screen resolutions, sizing images, and splitting a bill — ratios are everywhere. Having a calculator that handles them accurately saves you from mental arithmetic errors.
Common ratio conversions
Here's a quick reference for some of the most common ratios and their equivalent fraction, decimal, and percentage forms.
| Ratio | Fraction | Decimal | Percentage | Simplest form |
|---|---|---|---|---|
| 1 : 1 | 1/1 | 1.0 | 100% | 1 : 1 |
| 1 : 2 | 1/2 | 0.5 | 50% | 1 : 2 |
| 1 : 3 | 1/3 | 0.333… | 33.33% | 1 : 3 |
| 1 : 4 | 1/4 | 0.25 | 25% | 1 : 4 |
| 1 : 5 | 1/5 | 0.2 | 20% | 1 : 5 |
| 2 : 3 | 2/3 | 0.666… | 66.67% | 2 : 3 |
| 3 : 4 | 3/4 | 0.75 | 75% | 3 : 4 |
| 2 : 5 | 2/5 | 0.4 | 40% | 2 : 5 |
| 3 : 5 | 3/5 | 0.6 | 60% | 3 : 5 |
| 4 : 5 | 4/5 | 0.8 | 80% | 4 : 5 |
| 5 : 6 | 5/6 | 0.833… | 83.33% | 5 : 6 |
| 7 : 8 | 7/8 | 0.875 | 87.5% | 7 : 8 |