Ratio Calculator | Free Simplify & Proportion Tool
Simplify ratios, solve proportions, scale ratios up or down, and convert ratios to fractions, percentages, and decimals. All in one free, easy-to-use tool.
📖 Want to understand your results?
Read our complete guide to the Ratio Calculator — with real-world examples, expert insights, and pro tips.
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How the Ratio Calculator Works
Our ratio calculator offers five powerful modes to handle any ratio scenario:
Simplify Ratio
Reduce any ratio to its simplest form. Enter 8:12 and get 2:3 — with the GCD calculation shown.
Find Missing Value
Solve proportions like 2:3 = 8:?. Enter three values and we'll find the missing number in seconds.
Ratio of 3 Numbers
Simplify three-part ratios like 6:9:15 → 2:3:5. Perfect for dividing quantities in three proportions.
Scale Ratio
Scale any ratio up or down by a factor. Double a 2:3 ratio to get 4:6, or halve it to get 1:1.5.
Convert Ratio
See any ratio as a fraction, percentage, and decimal. Plus a quick reference table of common ratio conversions.
Visual Bars
Every result includes a visual bar chart showing the proportional relationship between parts.
Ratio Formulas Explained
Simplifying Ratios
Find the GCD (Greatest Common Divisor) and divide both parts.
Formula: A:B → (A÷GCD) : (B÷GCD)
Example: 8:12 → GCD=4 → 8÷4 : 12÷4 → 2:3
Proportions (Missing Value)
Cross-multiply to solve for the unknown.
Formula: A:B = C:D → D = (B × C) ÷ A
Example: 2:3 = 8:? → ? = (3 × 8) ÷ 2 = 12
Scaling Ratios
Multiply both parts by the scale factor.
Formula: A:B → (A×F) : (B×F)
Example: 2:3 × 4 = 8:12
Ratio Conversions
Convert between ratio, fraction, percentage, and decimal.
Fraction: A/B → %: (A÷B)×100 → Decimal: A÷B
Example: 3:4 = 3/4 = 75% = 0.75
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Common Aspect Ratios Reference
Aspect ratios are used in photography, video, screen design, and printing.
| Ratio | Name | Use Case | Example Resolution |
|---|---|---|---|
| 1:1 | Square | Instagram photos, profile pictures | 1080×1080 |
| 4:3 | Standard | Old TVs, tablets, photography | 1024×768 |
| 3:2 | Classic Photo | 35mm film, DSLR photos | 1200×800 |
| 16:9 | Widescreen | HD TV, YouTube, monitors | 1920×1080 |
| 16:10 | Wide | Computer monitors, tablets | 1920×1200 |
| 9:16 | Portrait | TikTok, Instagram Stories, Reels | 1080×1920 |
| 21:9 | Ultrawide | Cinema, ultrawide monitors | 2560×1080 |
| 5:4 | Large Format | Print photography | 1280×1024 |
Real-World Ratio Applications
Cooking & Baking
Scale recipes using ratios. A 1:2 flour-to-liquid ratio for 4 servings can be scaled to feed 10 people by finding the missing proportion.
Design & Media
Maintain aspect ratios when resizing images, videos, or screen designs. A 16:9 video at 1920×1080 scales down to 1280×720 at the same ratio.
Finance & Business
Profit sharing ratios, investment splits, debt-to-income ratios, and employee headcount ratios all use the same math under the hood.
Reviewed by Emily Watson, M.Ed.
Mathematics EducatorMathematics teacher and curriculum designer with 15+ years of experience.
Ratio Calculator Pros & Cons
Pros
- ✅ Five calculation modes in one tool
- ✅ Visual bar chart for every result
- ✅ Supports 2-number & 3-number ratios
- ✅ Free forever — no subscriptions
- ✅ Works offline after page load
Cons
- ✗ No batch ratio comparison
- ✗ No ratio scaling with unit conversion
Frequently Asked Questions
How do I simplify a ratio?
Find the GCD (Greatest Common Divisor) of both numbers, then divide both by it. For example, 8:12 — the GCD of 8 and 12 is 4, so 8÷4 = 2 and 12÷4 = 3, giving 2:3.
How do I find a missing value in a proportion?
Use cross-multiplication. If A:B = C:D, then D = (B × C) ÷ A. For example, 2:3 = 8:? → D = (3 × 8) ÷ 2 = 12.
What is a ratio of 3 numbers?
A three-part ratio compares three quantities, like 6:9:15. To simplify, find the GCD of all three numbers and divide each by it. 6:9:15 → GCD=3 → 2:3:5.
What does aspect ratio mean?
Aspect ratio is the proportional relationship between width and height of a screen or image. 16:9 means the width is 16 units for every 9 units of height. Common ratios include 16:9 (widescreen), 4:3 (standard), and 1:1 (square).
How do I convert a ratio to a percentage?
Divide the first number by the second, then multiply by 100. For example, 3:4 = 3÷4 = 0.75 × 100 = 75%. Our Convert Ratio mode shows this instantly.
How do I scale a ratio?
Multiply both parts of the ratio by the scale factor. To double a 2:3 ratio, multiply by 2: 2×2 = 4 and 3×2 = 6, giving 4:6. Use the Scale Ratio mode to scale up or down.
Want to Learn More?
Check out our comprehensive guide for in-depth explanations, real-world examples, and expert tips.
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