Ratio Calculator
Ratio calculator: solve A : B = C : D for a missing term, check two ratios, simplify (12 : 18 becomes 2 : 3) or split a total, so 25 in 3 : 2 is 15 and 10. How it works
Use the Ratio Calculator
About the Ratio Calculator
To solve a proportion A : B = C : D, cross-multiply: A × D = B × C. For 1 : 2 = 10 : D that gives D = 2 × 10 ÷ 1 = 20. This ratio calculator solves for whichever term you leave empty, checks whether two ratios are equal, reduces a ratio such as 12 : 18 to 2 : 3 (a 40% and 60% split, with equivalents 4 : 6 and 6 : 9), and splits a total in a ratio: 25 split 3 : 2 is 15 and 10.
Common ratios in simplest form
| Ratio | Simplest form | As 1 : n |
|---|---|---|
| 1920 : 1080 | 16 : 9 | 1 : 0.5625 |
| 1280 : 720 | 16 : 9 | 1 : 0.5625 |
| 2560 : 1440 | 16 : 9 | 1 : 0.5625 |
| 3840 : 2160 | 16 : 9 | 1 : 0.5625 |
| 1024 : 768 | 4 : 3 | 1 : 0.75 |
| 2560 : 1080 | 64 : 27 | 1 : 0.421875 |
| 4 : 6 | 2 : 3 | 1 : 1.5 |
| 12 : 18 | 2 : 3 | 1 : 1.5 |
| 150 : 100 | 3 : 2 | 1 : 0.6666666667 |
| 45 : 60 | 3 : 4 | 1 : 1.333333333 |
| 1.5 : 2.5 | 3 : 5 | 1 : 1.666666667 |
| 8.5 : 11 | 17 : 22 | 1 : 1.294117647 |
| 2 : 4 : 6 | 1 : 2 : 3 | 1 : 2 : 3 |
| 8 : 12 : 20 | 2 : 3 : 5 | 1 : 1.5 : 2.5 |
The simplest form is exact. The 1 : n form is rounded to 10 significant digits.
Solved proportions
| Proportion | Answer |
|---|---|
| 1 : 2 = 10 : D | D = 20 |
| 3 : 4 = 15 : D | D = 20 |
| 2 : 5 = C : 40 | C = 16 |
| A : 8 = 3 : 4 | A = 6 |
| 4 : B = 10 : 25 | B = 10 |
| 16 : 9 = 1280 : D | D = 720 |
| 16 : 9 = C : 1080 | C = 1920 |
| 1 : 16 = C : 500 | C = 31.25 |
| 5 : 8 = C : 100 | C = 62.5 |
The letter marks the field left empty. The first row is the example the calculator opens with.
How to use this tool
- Choose Solve a proportion, Simplify a ratio or Split a total.
- To solve, fill in three of A, B, C and D and leave the unknown empty. Fill in all four to check whether the two ratios are equal.
- To simplify, enter two or three terms greater than 0. The result is shown in whole numbers and in the form 1 : n, with five equivalent ratios; a two-term ratio adds its decimal, fractions of the whole and percent split.
- To split, enter the total and two or three terms greater than 0. Each part is listed with its term.
Frequently asked questions
- How do I solve a ratio for a missing number?
- Cross-multiply and divide. In 3 : 4 = 15 : D, multiply 4 by 15 and divide by 3: D = 20. In 2 : 5 = C : 40, multiply 2 by 40 and divide by 5: C = 16. Fill in all four fields instead and it checks the ratios: 2 : 3 and 4 : 6 are equal because 2 × 6 and 3 × 4 are both 12, while 2 : 3 and 4 : 7 are not.
- How do I simplify a ratio?
- Divide every term by their greatest common divisor. 12 and 18 both divide by 6, so 12 : 18 is 2 : 3. 1920 and 1080 both divide by 120, so 1920 : 1080 is 16 : 9. A two-term ratio also shows as a decimal, fractions and a percent split: 2 : 3 is 0.6666666667, 2/5 and 3/5 of the whole, 40% and 60%.
- What is the aspect ratio of 1920 × 1080?
- 16 : 9. So are 1280 × 720, 2560 × 1440 and 3840 × 2160. To find the height that matches a width, solve 16 : 9 = 1280 : D, which gives D = 720.
- How do I find equivalent ratios?
- Multiply every term of the simplest form by the same whole number. Simplify 12 : 18 and the list shows 2 : 3, 4 : 6, 6 : 9, 8 : 12 and 10 : 15. With the start multiplier and step both set to 10, 16 : 9 lists 160 : 90, 320 : 180, 480 : 270, 640 : 360 and 800 : 450.
- Can a ratio have decimals or three parts?
- Yes. The simplifier scales decimals up to whole numbers first, so 1.5 : 2.5 becomes 3 : 5, and it takes an optional third term: 8 : 12 : 20 reduces to 2 : 3 : 5. Fractions such as 1/2 are not accepted, so type 0.5.
- How do I split an amount in a ratio, such as 100 in the ratio 3 : 2?
- Choose Split a total, type 100 and the terms 3 and 2: the parts are 60 and 40. Each part is the total × its term ÷ the sum of the terms, here 100 × 3 ÷ 5 and 100 × 2 ÷ 5. A third term splits three ways, and decimal terms work too: 80 split 1.5 : 2.5 is 30 and 50.
Related Tools
View all toolsGolden Ratio Calculator & Visualizer
Enter any length to get its golden ratio pair: the value multiplied and divided by φ (1.618). View it as a golden rectangle, spiral or line split.
Fibonacci Sequence Generator
Fibonacci numbers from any two starting values: the first 1 to 1000 terms, the exact nth term up to n = 10,000, and the golden ratio estimate.
Arithmetic Sequence Calculator
Arithmetic sequence nth term aₙ = a₁ + (n − 1)d and sum Sₙ of the first n terms, with the first 20 terms listed and the position of any value.
Basic Calculator
Basic calculator for + − × ÷ in the standard order of operations (2 + 3 × 4 = 14), with % and memory keys, ^ for powers and the result as a fraction.
Decimal to Fraction
Convert a decimal to a fraction in lowest terms and see the working: 0.75 = 3/4, 2.75 = 11/4 or 2 3/4, and 0.333… (3 repeating) = 1/3.
Derivative Calculator
Enter f(x) and a point x = a to get f′(a), f(a), the tangent line and its graph, plus the formula for f′(x). Flags corners, jumps and vertical tangents.