Quick answer
A ratio a : b can be written as the fraction a/b. The ratio 3 : 4 is the fraction 3/4.
Enter whole-number parts. The calculator returns the fraction.
Related tools: Fraction to Ratio Calculator: Convert a fraction to a ratio. Fraction Calculator: Add, subtract, multiply and divide fractions with simplified and mixed-number results. Ratio Calculator: Simplify a ratio of two whole numbers.
How to use the Ratio to Fraction Calculator
- Enter a (a whole number, 0 or more).
- Enter b (a whole number, 1 or more).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| A | A whole number | ≥ 0 |
| B | A whole number | ≥ 1 |
Formula and method
Formula
a : b = a/b
IEEE-754 double precision; shown to at most 6 decimal places.
Direct conversion using the GCD to simplify.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: A = 3; B = 4.
| Result | Value |
|---|---|
| Fraction | 3/4 |
Example 2
Inputs: A = 10; B = 4.
| Result | Value |
|---|---|
| Fraction | 5/2 |
The first line is the headline result (fraction). IEEE-754 double precision; shown to at most 6 decimal places.
Part to part versus part to whole
The fraction 3/4 compares A to B. If the ratio describes parts of a whole, A is 3/(3 + 4) = 3/7 of the whole. Choose the version you need.
Simplifying
6 : 8 gives 6/8, which simplifies to 3/4. Both values must be whole numbers and the second must be positive.
From a ratio to shares of a total
The calculator reads a : b as the fraction a/b, so 3:4 gives 3/4. If 3 and 4 are two parts of one group, such as boys and girls, each share of the total is 3/7 and 4/7 instead.
For a three-part ratio such as 2:3:5, add the parts to get 10 and divide each by 10: the shares are 1/5, 3/10 and 1/2.
How the result changes with a
Holding every other input at the first worked example, this table changes only a. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| A | Fraction |
|---|---|
| 2 | 1/2 |
| 3 | 3/4 |
| 6 | 3/2 |
| 12 | 3 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- B: entering "0" shows "B must be at least 1." beside that field and no result.
Choosing between the Ratio to Fraction Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Fraction to Ratio Calculator](/math/fraction-to-ratio-calculator/) | numerator and denominator | Ratio |
| [Fraction Calculator](/math/fraction-calculator/) | numerator 1, denominator 1 and operation | Result |
| [Ratio Calculator](/math/ratio-calculator/) | first number and second number | Simplified ratio |
| [Inch Fraction Calculator](/math/inch-fraction-calculator/) | decimal inches and nearest | Nearest fraction |
| [Fraction to Decimal Calculator](/math/fraction-to-decimal-calculator/) | numerator and denominator | Decimal |
Background: rounding and basic arithmetic
Rounding to a place looks at the digit just to its right: 0 to 4 rounds down and 5 to 9 rounds up (the half-up convention, so 2.5 becomes 3). Rounding 838.274 gives 800 to the nearest hundred, 840 to the nearest ten and 838 to the nearest one.
Some systems use banker's rounding (half to even), which sends 2.5 to 2 and 3.5 to 4; check which convention your task requires, and round only at the end of a multi-step calculation.
Assumptions and limitations
- Whole numbers
- Second value must be positive
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for b to confirm this.
Frequently asked questions
What fraction is 2:5?
2/5 as part to part; 2/7 of the whole.
What is 1:3 as a fraction of the whole?
In the ratio 1:3 the first part is 1 of 4 equal parts, so it's 1/4 of the whole.
Can a ratio have a decimal?
Scale to whole numbers first.
How do I turn a three-part ratio into fractions?
Add the parts and divide each part by the total. For 2:3:5 the total is 10, so the fractions are 2/10, 3/10 and 5/10.
Are 6:8 and 3:4 the same ratio?
Yes. Dividing both numbers by 2 turns 6:8 into 3:4, and the fraction 6/8 reduces to 3/4.
What does the Ratio to Fraction Calculator calculate?
Convert a ratio a:b to a fraction a/b. It returns Fraction.
What formula does the Ratio to Fraction Calculator use?
a : b = a/b. Direct conversion using the GCD to simplify.
What do I need to enter in the ratio to Fraction Calculator?
You enter A and B.
How is the result rounded or limited?
IEEE-754 double precision; shown to at most 6 decimal places. Whole numbers.
What are the limits of this calculator?
Whole numbers. Second value must be positive.
What is an example of a ratio to Fraction result?
With a 3 and b 4, the fraction is 3/4.
Related calculators
- Fraction to Ratio Calculator — Convert a fraction to a ratio.
- Fraction Calculator — Add, subtract, multiply and divide fractions with simplified and mixed-number results.
- Ratio Calculator — Simplify a ratio of two whole numbers.
- Inch Fraction Calculator — Convert decimal inches to the nearest fractional inch.
- Fraction to Decimal Calculator — Convert a fraction to a decimal, showing repeating digits.
- Ratio Percentage Calculator — Percentage share of each part of a ratio.
Sources
- OpenStax, Prealgebra 2e (Rice University): fractions, decimals, percents, ratios and rounding
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.