Mole Calculator

Convert between mass, moles, molecular weight, and number of molecules for any chemical substance.

Supports 13 mass units, 4 molar mass units, 5 mole units, and 7 scientific notation scales.

Updated August 30, 2026

CreatorFrank Zhao

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Introduction / overview

The mole is the SI unit for amount of substance, and it's the bridge between the atomic scale you can't see and the gram-scale quantities you measure on a laboratory balance. One mole of any substance contains exactly $6.02214076 \times 10^{23}$ particles — a number known as Avogadro's constant.

Enter any two of mass, molecular weight, or moles — and the calculator instantly derives the third. Expand the molecules section to also see the particle count.

This calculator handles the three most common stoichiometric conversions in one place: grams to moles, moles to grams, and moles to molecules. It supports 13 mass units (from nanograms to metric tons, plus pounds, ounces, and atomic mass units), 4 molar mass units, 5 mole scales, and 7 scientific notation ranges for particle counts.

How to use / quick start

1Enter the molecular weight of your substance in g/mol. For water ( $\mathrm{H_2O}$ ), this is $18.015\ \mathrm{g/mol}$ .
2Enter the mass in grams (or switch to any supported unit — mg, kg, oz, lb, etc.). For 36 g of water, type 36.
3The moles field updates automatically. Expand the "Number of molecules" section to see the particle count in scientific notation.

Worked example: ethanol (C₂H₅OH)

Ethanol has a molecular weight of $46.07\ \mathrm{g/mol}$ . If you pour $23.035\ \mathrm{g}$ of ethanol into a flask:

n = \frac{m}{M} = \frac{23.035}{46.07} = 0.5\ \mathrm{mol}

That's exactly half a mole. If you expand the molecules section, you'll see approximately $3.011 \times 10^{23}$ ethanol molecules.

Reverse: finding molecular weight from mass and moles

You dissolve $5.844\ \mathrm{g}$ of table salt and measure $0.1\ \mathrm{mol}$ . The calculator derives:

M = \frac{m}{n} = \frac{5.844}{0.1} = 58.44\ \mathrm{g/mol}

The result $58.44\ \mathrm{g/mol}$ matches the known molar mass of NaCl — confirming the substance is pure sodium chloride.

Calculation method

The calculator is built on two fundamental stoichiometric relationships. Both are fully bidirectional — enter any two known quantities and the third is derived automatically.

Mass–mole link

m = M \times n

m = M \times n

n = \frac{m}{M}

Mole–molecule link

N = n \times N_{\mathrm{A}}

N = n \times N_{\mathrm{A}}

n = \frac{N}{N_{\mathrm{A}}}

Variable definitions

\mathrm{m}

Massany mass unit

\mathrm{M}

Molecular weightg/mol

\mathrm{n}

Molesamount of substance

\mathrm{N}

Moleculesparticle count

⇅

The two relationships share the

n

variable — entering mass + molecular weight first solves for moles, then immediately computes the particle count. This chain works in any direction: enter molecules & molecular weight to find mass, or enter mass & molecules to find molecular weight.

Avogadro's constant used by this calculator is the 2019 SI exact value: $N_{\mathrm{A}} = 6.02214076 \times 10^{23}\ \mathrm{mol}^{-1}$ . All internal calculations use high-precision decimal arithmetic, so results remain accurate even for very small or very large quantities.

Real-world examples

Caffeine (C₈H₁₀N₄O₂) — your morning coffee

Molecular weight: $194.19\ \mathrm{g/mol}$

A standard cup of coffee contains about $95\ \mathrm{mg}$ of caffeine. How many moles and molecules is that?

n = \frac{m}{M} = \frac{0.095}{194.19} \approx 4.89 \times 10^{-4}\ \mathrm{mol}

N \approx 4.89 \times 10^{-4} \times 6.022 \times 10^{23} \approx 2.95 \times 10^{20}\ \mathrm{molecules}

A single cup delivers roughly 2.95 × 10²⁰ caffeine molecules — less than a millimole, but enough to block adenosine receptors in your brain and keep you alert.

Glucose (C₆H₁₂O₆) — blood sugar

Molecular weight: $180.16\ \mathrm{g/mol}$

Your body maintains blood glucose at about $1\ \mathrm{g/L}$ . In $5\ \mathrm{L}$ of blood, that's $5\ \mathrm{g}$ of glucose. How many moles is circulating in your bloodstream?

n = \frac{m}{M} = \frac{5}{180.16} \approx 0.0278\ \mathrm{mol}

About 27.8 millimoles of glucose — a useful number for understanding why blood sugar is measured in mmol/L in many countries. Switch the mole unit to mmol in the calculator and you'll see the result directly.

Silver (Ag) — jewelry & electronics

Atomic weight: $107.87\ \mathrm{g/mol}$

A silver ring typically weighs about $5\ \mathrm{g}$ . How many silver atoms does that contain?

n = \frac{5}{107.87} \approx 0.0464\ \mathrm{mol}

N \approx 0.0464 \times 6.022 \times 10^{23} \approx 2.79 \times 10^{22}\ \mathrm{atoms}

A 5-gram ring contains nearly 28 sextillion silver atoms. Each atom contributed one free electron that gives silver its exceptional electrical conductivity — which is why it's used in high-end electronics and contacts.

Tips & best practices

Match your unit to your data

If your balance reads in milligrams, switch the mass unit to mg before typing the number. This avoids manual conversion errors — the calculator handles all unit math internally.

Molecular weight is not atomic weight

For diatomic elements like O₂ or N₂, use twice the atomic weight: O₂ = 32 g/mol, not 16. For hydrated compounds like CuSO₄·5H₂O, include the water molecules in the molecular weight.

Use the molecules section for very small quantities

When working with micrograms or nanomoles, the molecule count can be more intuitive than a tiny mole value. Expand the "Number of molecules" section and pick a convenient ×10ⁿ scale.

Verify with known values

A good sanity check: 1 mole of water (M = 18.015 g/mol) weighs exactly 18.015 g. If your calculation doesn't match this, double-check the molecular weight you entered.

Limitations

Pure substances only. The mass–mole relationship assumes you are working with a pure compound. For mixtures or impure samples, additional information is needed before this calculation applies.
You must provide the molecular weight. The calculator does not look up chemical formulas from a database. Use a periodic table or our molar mass calculator to compute it from the formula.
All values must be positive. Mass, molecular weight, moles, and molecule count are all physical quantities that cannot be zero or negative in this context.
Standard SI definitions. The calculator uses the exact 2019 SI value of Avogadro's constant ( $6.02214076 \times 10^{23}\ \mathrm{mol}^{-1}$ ). It does not model temperature-dependent effects on molar volume or gas behaviour — for those, use a dedicated gas law calculator.

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