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Chemistry Tools · Updated October 21, 2026 · Reviewed by FormatFlow Editorial

Molar Mass Calculator

You can calculate the molar mass of a chemical formula in g/mol, see how much each element contributes and what percentage of the total it makes up, with nested brackets and hydrate notation supported.

Runs in your browserFree · No sign-up · No watermark
FORMULA → MASSRuns in your browser
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Everything runs locally in this tab. No file is uploaded while the tool loads.

This tool runs in your tab. Nothing is uploaded and no copy is stored.

How files are handled

At a glance

Works with
FORMULA → MASS
Processing
In your browser
Price
Free, no account
Updated
October 21, 2026
All Chemistry Tools

About Molar Mass Calculator

Molar mass is the mass of one mole of a substance, numerically equal to its formula mass in atomic mass units but written in grams per mole. Getting it right is the first step in almost every stoichiometry problem: without it you cannot turn a weighed mass into moles, and without moles you cannot use a balanced equation.

This calculator parses the formula you type, including nested brackets such as Al2(SO4)3 and hydrate notation such as CuSO4·5H2O. It works through the element totals, multiplies each by its standard relative atomic mass and adds the results, then shows the contribution and percentage of every element so a mistyped subscript is easy to spot.

What this tool does

The details that matter when you use Molar Mass Calculator for real work.

  • Nested brackets and hydrates

    Round, square and curly brackets can be nested, and hydrate dots accept an integer coefficient such as the 5 in CuSO4·5H2O.

  • Per-element breakdown

    Each element gets its atom count, relative atomic mass, mass contribution and percentage of the total, which is the data needed to check a formula or find a mass fraction.

  • Step-by-step working

    The calculation is written out with each atomic mass multiplication and the final sum, so the result can be followed by hand or copied into notes.

  • 118-element table

    All 118 elements are supported with standard atomic weights, and the full table is available on the page for checking a value.

  • Strict formula validation

    Unknown symbols, unbalanced or mismatched brackets, zero subscripts and stray numbers are reported with a specific message instead of being guessed at.

  • Local and instant

    Parsing and arithmetic run in the browser as you type, so formulas from coursework or lab work never leave the device.

How to use Molar Mass Calculator

No account, no installation — the whole job happens in this browser tab.
  1. 01

    Type the formula

    Enter the formula with normal digits for subscripts, for example Ca(OH)2 or Al2(SO4)3; Unicode subscripts such as H₂O are accepted too.

  2. 02

    Use brackets for groups

    Wrap repeating groups in (), [] or {} and put the multiplier after the closing bracket, as in Ca(OH)2.

  3. 03

    Add hydrate water

    Write hydrate dots as a middle dot or period, for example CuSO4·5H2O, and put the water coefficient after the dot.

  4. 04

    Read the breakdown

    Check the headline molar mass, then the element table for atom counts, contributions and percentages.

  5. 05

    Follow the working

    Use the step-by-step panel to check each atomic mass multiplication and the final addition.

How this tool works

Works with
FORMULA → MASS
Processing
Client-side, in your browser. Nothing is uploaded.
Requirements
Chrome, Edge, Firefox or Safari · JavaScript enabled

Limitations worth knowing

  • Uses standard atomic weights only: isotope-specific masses and isotopic purity are not handled.
  • Neutral formulas only: charges, oxidation states and coefficients in front of a formula are rejected rather than parsed.
  • Fractional subscripts, as used in some mineral formulas, are not supported, and results are rounded to three decimal places.
  • Elements with no stable isotope use the mass number of their longest-lived isotope, so those molar masses are approximate.

Privacy and file handling

Formulas are parsed and the molar mass is calculated in your browser tab. Nothing you type is uploaded, stored or logged, and the calculator makes no network request.

Read the full privacy policy

Molar Mass Calculator FAQ

Short, direct answers to the questions people ask before using this tool.
What is the difference between molar mass and molecular weight?
Molar mass is the mass of one mole in grams per mole; molecular weight is a dimensionless ratio relative to one twelfth of a carbon-12 atom. The numbers are numerically the same for ordinary compounds, so a molecular weight of 18.015 corresponds to a molar mass of 18.015 g/mol.
How do hydrates like CuSO4·5H2O work?
The dot separates the salt from the water of crystallization, and the number before the water formula multiplies that part. Copper(II) sulfate pentahydrate therefore contributes one CuSO4 unit plus five H2O units, and the calculator shows both part masses separately.
Why does my textbook value differ from this result?
Textbooks often round atomic masses to one or two decimals or use older values, while this calculator uses standard IUPAC atomic weights. The difference is usually in the second or third decimal place, and for coursework either result is normally accepted if you show the values you used.
Are square and curly brackets supported?
Yes. Round, square and curly brackets can all be used for groups and can be nested, so a formula written as K4[Fe(CN)6] parses correctly. The brackets must be balanced and each closing type must match its opening type.
Why does CO give a different result from Co?
Element symbols are case-sensitive: Co is cobalt, while CO is one carbon atom plus one oxygen atom, which is carbon monoxide. The parser rejects impossible symbols, so a lowercase start such as h2o produces an error instead of a wrong mass.
Does it handle isotopes or ionic charges?
No. The calculation uses standard relative atomic masses and neutral formulas only, so isotope labels such as 13C, ionic charges such as SO4 2- and coefficients in front of a formula are not accepted. Use isotope masses from a data table when you need them.
How precise is the molar mass result?
The total is rounded to three decimal places and each contribution is shown to three decimals, with percentages to two decimals. That is more than enough for coursework and routine lab calculations, but it is not intended for analytical metrology.
Why is my formula rejected when it looks correct?
The usual causes are an unbalanced bracket, a number placed where an element symbol should be, a lowercase letter at the start, or a stray space inside a symbol. The error message names the problem so it can be fixed in the formula box.

Background reading

Format guides that explain the trade-offs behind Molar Mass Calculator.