Fraction to Percent Calculator

How fraction to percent works

How to convert a fraction to a percent (two steps)

1. 1Divide the numerator by the denominator to get the decimal.
2. 2Multiply the decimal by 100 and add the percent sign.

Percent means per hundred, so multiplying the decimal by 100 gives the parts out of 100. The value stays the same; only the way it is written changes.

A shortcut for denominators that divide 100

When the denominator goes into 100 exactly (2, 4, 5, 10, 20, 25 or 50), scale the fraction to a denominator of 100. For 15/20, multiply the top and bottom by 5 to get 75/100, which is 75%. For 13/25, multiply by 4 to get 52/100, or 52%. The multipliers are 50 for halves, 25 for quarters, 20 for fifths, 10 for tenths, 5 for twentieths, 4 for twenty-fifths and 2 for fiftieths.

Improper fractions and mixed numbers

When the numerator is larger than the denominator the fraction is more than 1, so the percent is more than 100. For a mixed number, convert it to an improper fraction first, then divide. The calculator does this when you fill in the whole-number field. Examples 2 and 3 below work through both cases.

Repeating decimals and rounding

Some fractions give decimals that never end. One third is 0.3333 and so on, which is 33.33% to two decimal places, and 2/3 is 66.67%. Round only at the end, because rounding the decimal first shifts the percent: 0.33 gives 33%, not 33.33%.

X out of Y as a percentage

A score of X out of Y is the fraction X/Y, so the method is identical. 15 out of 20 as a percentage is 15/20, which is 75%. Check any of the 68 popular scores in the lookup table below.

Fraction to percentage in Excel and Google Sheets

With the numerator in A2 and the denominator in B2, type =A2/B2 and format the cell as a percentage. No × 100 is needed, because the percent format does it for you.

Fraction to percent chart and examples

Fraction to percent chart

This percentage chart lists the most common fractions, with decimals rounded to four places:

X out of Y as a percentage: lookup table

The most-searched scores, sorted by the total. 27 out of 30 as a percentage is 90%, 25 out of 30 as a percentage is 83.33% and the 24/30 percentage is 80%. Small unit fractions are quick: 1/10 as a percent is 10%, 1/20 as a percent is 5% and 3/20 as a percent is 15%.

Fraction to percent code

Both versions reproduce the examples above (75%, 175%, 250%, 58.33%, 85%) and the lookup table, reject non-numeric input and refuse a zero denominator.

JavaScript

1function finite(name, v) {2  if (typeof v !== "number" || !Number.isFinite(v)) throw new TypeError(`${name} must be a finite number`);3}4​5export function fractionToPercent(numerator, denominator, decimals = 2) {6  finite("numerator", numerator);7  finite("denominator", denominator);8  if (denominator === 0) throw new RangeError("denominator must not be 0");9  if (!Number.isInteger(decimals) || decimals < 0 || decimals > 10) throw new RangeError("decimals must be a whole number from 0 to 10");10  return Number(((numerator / denominator) * 100).toFixed(decimals));11}12​13export function mixedToPercent(whole, numerator, denominator, decimals = 2) {14  finite("whole", whole);15  finite("numerator", numerator);16  finite("denominator", denominator);17  if (denominator === 0) throw new RangeError("denominator must not be 0");18  if (!Number.isInteger(decimals) || decimals < 0 || decimals > 10) throw new RangeError("decimals must be a whole number from 0 to 10");19  const sign = whole < 0 ? -1 : 1;20  const value = sign * (Math.abs(whole) + numerator / denominator);21  return Number((value * 100).toFixed(decimals));22}

Python

1from decimal import Decimal, ROUND_HALF_UP2import math3​4​5def _num(name, v):6    if isinstance(v, bool) or not isinstance(v, (int, float, Decimal)) or not math.isfinite(float(v)):7        raise ValueError(f"{name} must be a finite number")8    return Decimal(str(v))9​10​11def _round(x, decimals):12    if not isinstance(decimals, int) or isinstance(decimals, bool) or not 0 <= decimals <= 10:13        raise ValueError("decimals must be a whole number from 0 to 10")14    return x.quantize(Decimal(1).scaleb(-decimals), rounding=ROUND_HALF_UP)15​16​17def fraction_to_percent(numerator, denominator, decimals=2):18    n, d = _num("numerator", numerator), _num("denominator", denominator)19    if d == 0:20        raise ValueError("denominator must not be 0")21    return _round(n / d * 100, decimals)22​23​24def mixed_to_percent(whole, numerator, denominator, decimals=2):25    w, n, d = _num("whole", whole), _num("numerator", numerator), _num("denominator", denominator)26    if d == 0:27        raise ValueError("denominator must not be 0")28    sign = -1 if w < 0 else 129    return _round(sign * (abs(w) + n / d) * 100, decimals)

mixedToPercent(2, 1, 2) returns 250, the mixed-number example. Round only for display. The Python version rounds half up with Decimal, which is the usual school convention; JavaScript's toFixed works on the binary value, so a value on a tie, such as 1.005, can round down where school convention rounds up.

Privacy and input safety

Values are calculated in your browser. The numbers you enter are not sent to a server or stored.

• Fields accept numbers only. Text, empty fields, NaN and Infinity are rejected with a message, and nothing you type is ever evaluated as code.
• A denominator of 0 returns a clear message instead of a division error, because a fraction cannot have a zero denominator.
• Decimal places are limited to a whole number from 0 to 10.
• A comma followed by exactly three digits is read as a thousands separator, so 1,200 is 1200. Any other comma is a decimal point, so 12,50 is 12.50, and a number starting with 0, such as 0,500, is read as a decimal. Mixed formats such as 1.234,5 and ambiguous entries such as 1,2,3 are refused instead of guessed. Spaces, including no-break spaces, between digit groups are ignored.

Common fraction to percent mistakes

Fraction, decimal and percentage: one value, five forms

The same value, 0.75, written five ways. How to turn a number into a percent depends on its form:

The fraction and X out of Y rows are the same calculation. The ratio row is the one people trip on: a ratio of 3:1 splits a whole into 4 parts, so the first part is 3/4, not 3/1.