What Is a Ratio?
A ratio expresses the relationship between two quantities — how many times one contains the other. Written as A:B (read "A to B"), it tells you the relative size of two values without specifying their actual amounts. A ratio of 3:1 means for every 3 of the first, there's 1 of the second.
How to Calculate a Ratio
- Write the two values as a fraction: A/B
- Find the Greatest Common Divisor (GCD) of A and B
- Divide both values by the GCD to simplify
- Write as A:B in simplest form
Example: What is the ratio of 24 to 36? GCD(24, 36) = 12. 24/12 = 2, 36/12 = 3. Ratio = 2:3
8 Real-World Examples
| # | Scenario | Values | Ratio |
|---|---|---|---|
| 1 | Recipe: flour to sugar | 300g : 100g | 3:1 |
| 2 | Map scale: 1cm = 5km | 1 : 500,000 | 1:500,000 |
| 3 | Class: 18 girls, 12 boys | 18 : 12 | 3:2 |
| 4 | Investment return: $150 profit on $1,000 | 150 : 1000 | 3:20 |
| 5 | Concrete mix: cement:sand:gravel | 1:2:4 | 1:2:4 |
| 6 | Screen resolution: 1920 × 1080 | 1920 : 1080 | 16:9 |
| 7 | Speed: 90 km/h for 120 km | 90 : 120 | 3:4 |
| 8 | Salary split: $4,500 and $3,000 | 4500 : 3000 | 3:2 |
Scaling Ratios Up and Down
If a recipe uses a 2:3 ratio of oil to vinegar and you want to make 500 mL total: total parts = 2 + 3 = 5. Each part = 500 ÷ 5 = 100 mL. Oil = 2 × 100 = 200 mL, Vinegar = 3 × 100 = 300 mL.
Common Mistakes
- Order matters: 3:2 and 2:3 are different ratios. Always specify which quantity comes first.
- Units must match: You can't directly ratio 500g to 2 kg without converting — 500g : 2,000g = 1:4.
- Simplify fully: 6:9 simplified to 2:3, not 3:4.5. Always find the GCD.
The ratio calculator below handles simplification, scaling, and equivalent ratios automatically — just enter your two values to get the result.
Calculate and simplify any ratio
Use the free Ratio Calculator on CalcPocket — no signup required.
Ratio Calculator