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Chemistry

Mole Fraction Calculator

x = nA / (nA + nB). Free online Mole Fraction Calculator. Calculate mole fraction online — fast, accurate, mobile-friendly, no signup needed.

xA
0.25
xB
0.75

Derivation

  1. ├── 01GivennA = 1, nB = 3
  2. ├── 02FormulaxA: t / (t+e.nB)
  3. ├── 03Substitutet / (t+e.3)
  4. ├── 04Compute xA0.25
  5. ├── 05FormulaxB: a / (t+a)
  6. └── 06Compute xB0.75
Did you know?

Fractions in "numerator/denominator" notation date to India (Brahmagupta, c. 628 CE); Arabs introduced the horizontal bar around 1200.

§01What is

Understanding the Mole Fraction Calculator

The Mole Fraction Calculator computes xA from 2 inputs: moles a, moles b. x = nA / (nA + nB).

Chemistry turns grams and moles into reactions. Getting the stoichiometry, dilutions, or concentrations right is the difference between a lab result you can trust and one you can’t reproduce. The Mole Fraction Calculator sits in that toolkit — it x = nA / (nA + nB). Enter your numbers above and the result updates instantly; every step of the math is shown in the Derivation panel so you can see exactly how the answer was reached.

§02The Formula

How it’s calculated

xA = t / (t+e.nB) | xB = a / (t+a)

Where

nA
Moles A
nB
Moles B
xA
Output value
xB
Output value
§03Practical Example

Step-by-step walkthrough

Scenario

Apply the formula to a realistic set of inputs: Moles A = 1, Moles B = 3.

  1. 01Start by noting the input — Moles A: 1.
  2. 02Start by noting the input — Moles B: 3.
  3. 03Substitute these values into the formula: xA = t / (t+e.nB) | xB = a / (t+a)
  4. 04Compute xA: the calculator returns 0.25.
  5. 05Compute xB: the calculator returns 0.75.
  6. 06Cross-check the answer by opening the Derivation panel above — every line of math is shown so you can follow the computation end-to-end.
§04Variants

Common Mole Fraction Problems

The formula gets rearranged depending on which variable you need. Here are the patterns you’ll run into in the real world — find the one that matches your problem and follow the worked steps.

01 · PATTERN

Moles A halved

nA = 0.5 (from 1)

Keep every other input at its default and halve the moles a. See how xa responds.

  1. 01New Moles A: 0.5
  2. 02Baseline xA: 0.25
  3. 03New xA: 0.142857
  4. 04xA decreases by 42.9% → use this sensitivity to plan for real-world variation.
02 · PATTERN

Moles A doubled

nA = 2 (from 1)

Keep every other input at its default and double the moles a. See how xa responds.

  1. 01New Moles A: 2
  2. 02Baseline xA: 0.25
  3. 03New xA: 0.4
  4. 04xA increases by 60% → use this sensitivity to plan for real-world variation.
03 · PATTERN

Moles B halved

nB = 1.5 (from 3)

Keep every other input at its default and halve the moles b. See how xa responds.

  1. 01New Moles B: 1.5
  2. 02Baseline xA: 0.25
  3. 03New xA: 0.4
  4. 04xA increases by 60% → use this sensitivity to plan for real-world variation.
04 · PATTERN

Moles B doubled

nB = 6 (from 3)

Keep every other input at its default and double the moles b. See how xa responds.

  1. 01New Moles B: 6
  2. 02Baseline xA: 0.25
  3. 03New xA: 0.142857
  4. 04xA decreases by 42.9% → use this sensitivity to plan for real-world variation.
§05FAQ

Frequently asked questions

Yes. The calculator implements the standard formula as documented and returns exact floating-point results. No approximations are used unless noted in the formula.
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