Toolarithm

Science Calculator

Molar Mass Calculator

Count atoms. Check the adopted mass.

Read a chemical formula

Count atoms. Check the adopted mass.

Case-sensitive symbols, integer subscripts, matched brackets and hydrate dots. No reaction coefficient, spaces, charge or isotope label.

View results

Calculation and report options

Three through ten; display precision does not improve physical atomic-weight certainty.

One UTF-8 formula in a text file up to 4 KiB; exported report CSV is not a formula template.

Worked examples

Up to 500 characters, twelve nested bracket levels, twelve adduct parts, integer multipliers through one million and one trillion expanded atoms. A period always separates adducts; it is never a fractional subscript. Subscript digits are normalized, while element capitalization is preserved.

Nominal molar mass

Ca(OH)2\mathrm{Ca}(\mathrm{O}\mathrm{H})_{2}M=74.0920 g mol−1M=74.0920\,\mathrm{g\,mol^{-1}}

Based on CIAAW 2024 abridged nominal values. Display uses 6 significant figures. Atomic-weight variability and measurement uncertainty are not propagated.

Composition summary

Adopted-decimal sum before rounding

Madopted=74.092 g mol−1M_{\mathrm{adopted}}=74.092\,\mathrm{g\,mol^{-1}}

The arithmetic is exact for the decimal weights selected here. The physical molar mass is an estimate based on those adopted data.

Atoms per molecule or formula unit

Natoms/entity=5N_{\mathrm{atoms/entity}}=5

All bracket and adduct multipliers are included. No reaction coefficient is treated as part of a species molar mass.

Aggregated formula in Hill order

CaH2O2\mathrm{Ca}\mathrm{H}_{2}\mathrm{O}_{2}

Carbon first and hydrogen second when carbon is present; remaining symbols alphabetically. Without carbon all symbols sort alphabetically. This is an aggregate composition, not a structural formula.

Simplest whole-number atom ratio

CaH2O2\mathrm{Ca}\mathrm{H}_{2}\mathrm{O}_{2}gcd⁡(atom counts)=1\gcd(\text{atom counts})=1

Reducing counts does not change which original formula was used for the reported molar mass. It does not identify a different real chemical species.

Element counts and mass contributions

Multiply each expanded atom count by its adopted nominal atomic weight. Element mass percentages use the unrounded sum; separately rounded percentages need not add to exactly one hundred. Published reference uncertainty is shown for context and is not propagated.

Element page 1 of 1. Distinct elements: 3. All rows remain in copy and CSV.

Calcium

nCa=1n_{\mathrm{Ca}}=1Aadopted(Ca)=40.078A_{\mathrm{adopted}}(\mathrm{Ca})=40.0781⋅40.078 g mol−1=40.078 g mol−11\cdot40.078\,\mathrm{g\,mol^{-1}}=40.078\,\mathrm{g\,mol^{-1}}wCa≈54.0922%w_{\mathrm{Ca}}\approx54.0922\%

CIAAW 2024 abridged nominal value.

Quoted reference uncertainty: ±0.004\pm0.004.

Hydrogen

nH=2n_{\mathrm{H}}=2Aadopted(H)=1.0080A_{\mathrm{adopted}}(\mathrm{H})=1.00802⋅1.0080 g mol−1=2.016 g mol−12\cdot1.0080\,\mathrm{g\,mol^{-1}}=2.016\,\mathrm{g\,mol^{-1}}wH≈2.72094%w_{\mathrm{H}}\approx2.72094\%

CIAAW 2024 abridged nominal value.

Quoted reference uncertainty: ±0.0002\pm0.0002.

Oxygen

nO=2n_{\mathrm{O}}=2Aadopted(O)=15.999A_{\mathrm{adopted}}(\mathrm{O})=15.9992⋅15.999 g mol−1=31.998 g mol−12\cdot15.999\,\mathrm{g\,mol^{-1}}=31.998\,\mathrm{g\,mol^{-1}}wO≈43.1868%w_{\mathrm{O}}\approx43.1868\%

CIAAW 2024 abridged nominal value.

Quoted reference uncertainty: ±0.001\pm0.001.

Step-by-step composition check

First expand each local bracket or adduct multiplier, then combine repeated elements. The count attached to a local group precedes any enclosing multiplier. Finally sum the decimal-exact contributions. These are composition steps, not a reaction mechanism or a test of chemical stability.

Group page 1 of 1. Total local expansions: 1.

  1. Local expansion 1

    (OH)2(\mathrm{O}\mathrm{H})_{2}nO=2,nH=2n_{\mathrm{O}}=2,\quad n_{\mathrm{H}}=2

Sum adopted contributions before rounding

Madopted=[1⋅40.078+2⋅1.0080+2⋅15.999] g mol−1=74.092 g mol−1M_{\mathrm{adopted}}=\left[1\cdot40.078+2\cdot1.0080+2\cdot15.999\right]\,\mathrm{g\,mol^{-1}}=74.092\,\mathrm{g\,mol^{-1}}

Long expression: full composition and adopted values remain in the on-screen mathematics, complete copy and CSV.

What Can You Create?

Create a traceable composition and nominal mass record

Expanded atom and mass contributions

Read each recognized element, its final atom count, the adopted nominal atomic weight and its contribution to the total. This exposes the multiplication hidden inside nested groups and repeated symbols. The source formula remains distinct from the aggregate composition, so reordering element cards cannot silently turn a structural grouping into a different chemical interpretation.

Mass percentages and sample conversions

Compare element mass percentages calculated from the unrounded adopted sum, then optionally convert a stated sample mass to amount or an amount to mass. Explicit unit choices prevent a milligram input from being interpreted as grams. Molecule or formula-unit counts are identified as bulk-amount estimates, with the total atom count based on the expanded formula.

An inspectable adopted-weight report

Keep the atomic-weight edition and every active override alongside the answer. Complete exports retain all contribution rows and local expansions even when the screen displays one page. A printed report focuses on the chosen view and makes long-expression limits visible, while copied and downloaded data preserve the full composition and arithmetic needed to reproduce the result.

Molar mass formulas and worked composition examples

For an ordinary chemistry estimate, sum the adopted relative atomic weights with their expanded atom counts: Madopted=∑iniAr,i g mol−1M_{\mathrm{adopted}}=\sum_i n_i A_{r,i}\,\mathrm{g\,mol^{-1}}. This is a stated numerical convention based on adopted nominal data, not an assertion that a physical sample or the atomic-weight reference is exact. Natural isotope composition can vary. Chemical formulas below describe composition; they are not balanced reaction equations.

Expand a hydroxide group

The outside subscript multiplies both oxygen and hydrogen inside the parentheses. Calcium has no explicit subscript, so it occurs once. Sum the adopted contributions only after these counts have been established.

Ca(OH)2:nCa=1,nO=2,nH=2\mathrm{Ca(OH)_2}:\quad n_{\mathrm{Ca}}=1,\quad n_{\mathrm O}=2,\quad n_{\mathrm H}=2

Sum before display rounding

Use the published nominal decimal values selected in this model. The sum remains available independently of the display significant figures, which helps explain differences from another atomic-weight table or a more coarsely rounded classroom answer.

Madopted=[40.078+2(15.999)+2(1.0080)] g mol−1=74.092 g mol−1M_{\mathrm{adopted}}=\left[40.078+2(15.999)+2(1.0080)\right]\,\mathrm{g\,mol^{-1}}=74.092\,\mathrm{g\,mol^{-1}}

Include the water in a hydrate

The adduct coefficient multiplies the entire water composition. Add its oxygen and hydrogen to the anhydrous part before forming mass fractions. The combined formula unit is the entity used for a subsequent amount conversion.

CuSO4⋅5H2O:nCu=1,nS=1,nO=9,nH=10\mathrm{CuSO_4\cdot5H_2O}:\quad n_{\mathrm{Cu}}=1,\quad n_{\mathrm S}=1,\quad n_{\mathrm O}=9,\quad n_{\mathrm H}=10

Convert a water sample with matching units

The sample converter uses the unrounded adopted water mass, not the displayed rounded value. The resulting amount is conditional on that nominal mass model and the stated sample input.

n=18.015 g18.015 g mol−1=1 moln=\frac{18.015\,\mathrm g}{18.015\,\mathrm{g\,mol^{-1}}}=1\,\mathrm{mol}
wi=niAr,i∑jnjAr,j×100%,N=nNAw_i=\frac{n_i A_{r,i}}{\sum_j n_j A_{r,j}}\times100\%,\qquad N=nN_A

The dimensional relationships are n=m/Mn=m/M and m=nMm=nM. The defined constant is NA=6.02214076×1023 mol−1N_A=6.02214076\times10^{23}\,\mathrm{mol^{-1}}. A sample entity may be a molecule or a formula unit, and the total atom estimate multiplies its entity count by the expanded atoms per entity. A reduced atom ratio, such as HO\mathrm{HO} from H2O2\mathrm{H_2O_2}, is a composition ratio only; the original peroxide formula still determines the molar mass in that calculation.

The distinction between arithmetic and measurement is practical. Exact decimal arithmetic prevents avoidable binary rounding during the adopted-weight sum, and rational arithmetic preserves a repeatable sample conversion before presentation rounding. Neither operation supplies missing information about isotope abundance, sample purity, balance calibration or physical uncertainty. Keep those assumptions with any result used outside a worked educational example.

Why Users Love This Tool

Separate a valid formula, adopted data and display precision

Strict composition handling

  • Every bracket must match and every written multiplier must be a positive bounded integer. Empty adduct parts and incomplete formulas are errors instead of being skipped or assigned a mass of zero.
  • Element capitalization is preserved, and unknown symbols or unsupported labels are identified before exporting a result. Parentheses, square brackets and braces can be nested within the declared depth limit.
  • Published standard weights and explicitly supplied adopted values have separate labels. A missing standard atomic weight cannot silently become a guessed isotope mass or an unexplained zero contribution.

A reproducible numerical model

  • The report names the CIAAW edition and retains the nominal decimals actually summed. Quoted reference uncertainties remain contextual rather than being combined into an unsupported compound uncertainty estimate.
  • Percentages and sample conversions start from the unrounded adopted sum. Significant-figure choices affect the displayed representation and do not overwrite the source counts or imply improved physical precision.
  • Paging, row ordering and hidden panels do not discard data from complete copies or CSV. Strict share links omit inactive buffers, while invalid imports preserve the existing calculation and later edits take precedence over delayed file reads.
Perfect For

For chemistry learning, composition checks and transparent estimates

Chemistry students

Practice translating subscripts and brackets into atom counts before multiplying by atomic weights. Compare an anhydrous formula with a hydrate, inspect the contribution of each element and follow a mass-to-amount conversion with units that cancel correctly.

Educators and laboratory learners

Prepare worked composition examples with the adopted reference data visible. Explain why natural isotope variation, a measured sample and extra printed digits are different issues. The tool supports educational checks rather than certifying a preparation, material identity or analytical method.

Readers comparing reference tables

Reproduce a nominal result using its recorded data edition, or enter a clearly identified adopted value for a specific comparison. The presence of every recognized element does not imply a published standard atomic weight exists for each one, and custom entries require their own external justification.

How It Works

How it works in three quick steps.

1

Enter and verify the chemical formula

Enter case-sensitive element symbols with positive integer subscripts. Match every parenthesis, square bracket or brace and use a middle dot between hydrate or adduct parts. Review the typeset formula and expanded atom counts before interpreting the mass. A leading reaction coefficient, charge, isotope label, fractional subscript or phase label is not part of the supported formula grammar and should not be silently reinterpreted.

2

Inspect adopted weights and contributions

Read the nominal molar mass together with the element contribution cards. Published values use the CIAAW 2024 abridged table. If you deliberately select adopted overrides, keep each replacement visible and supply your own reference for it. Elements without a published standard atomic weight require such an explicit value. Adjust display significant figures without assuming that additional printed digits improve the physical certainty of the atomic-weight data.

3

Convert a sample and retain the working

Optionally choose mass to amount or amount to mass, enter a nonnegative sample value and select a compatible unit. The conversion uses the unrounded adopted molar mass and reports molecules or formula units as appropriate. Copy the complete report or formula LaTeX, download all composition and exact adopted-input certificates as CSV, share active settings, or print the visible report after selecting the element and group pages you want to explain.

Download & Print

Keep the adopted data with the mathematical answer

Copy the report or LaTeX

Copy summary preserves every element and local expansion, the nominal mass before rounding and the active sample calculation. Copy LaTeX supplies the safely generated chemical formula and complete adopted-contribution sum. This retains actual mathematical notation for a compatible document editor without inserting the raw editable formula as trusted LaTeX.

Download complete composition CSV

The four-column report stores element counts, adopted weights, data-source labels, exact decimal contributions and rational mass-percentage certificates in separate rows. Active sample conversions retain exact numerator and denominator certificates for the adopted input model. Long integer cells are marked as text to protect their digits in spreadsheets; generated report headings are not a one-formula import template.

Print the selected report pages

Choose the element and group pages you need, then use Print / Save PDF. Input controls and unrelated navigation are removed while the adopted-data scope remains. Long chemical expressions receive explicit print notices rather than clipped digits. The on-screen mathematics and complete copy or CSV preserve full composition when a small sheet cannot show it conveniently.

FAQ

Frequently Asked Questions

Which atomic weights does this molar mass calculator use?
The default library contains the CIAAW Abridged Standard Atomic Weights 2024 nominal values for eighty-four elements and identifies all one hundred eighteen named elements. The table's nominal decimals and quoted reference uncertainties remain distinct. This calculator does not propagate those uncertainties into a compound uncertainty estimate. For an element without a published standard atomic weight, supply an explicit adopted value rather than expecting the tool to invent a standard weight or choose an isotope automatically.
How do parentheses, square brackets and hydrates affect atom counts?
A positive integer after a bracket group multiplies every atom inside that group, including counts already expanded from nested groups. An adduct coefficient multiplies the entire part following the separator. The element cards combine repeated symbols across all parts before calculating contributions. Local expansion steps show each group before any enclosing multiplier, while the final composition summary includes every multiplier. Hydrate water is therefore included in the total molar mass and mass percentages.
Why should I use a middle dot rather than a period for a hydrate?
A middle dot makes the intended separation between adduct parts clear. A period is accepted for compatibility, but it always means an adduct separator in this grammar and never a decimal subscript. The tool displays a notice and renders the resulting composition so that this interpretation can be checked. Fractional stoichiometric subscripts are unsupported. If a pasted formula was intended to contain a fractional count, rewrite the problem with an appropriate model instead of treating that period as a decimal point here.
Does a reaction coefficient change the molar mass of the species?
A reaction coefficient changes how much of a species participates; it does not change that species' per-mole molar mass. This tool rejects a leading coefficient on the first formula part so that a reaction amount cannot be mistaken for a different compound composition. Put the desired amount in the sample conversion controls instead. Coefficients after adduct separators have a different role: they describe the relative composition of the combined hydrate or adduct formula unit.
Can I calculate charged ions, isotope patterns or radioactive elements?
Charge notation, electron-mass corrections, isotope labels and isotope-distribution calculations are outside this formula parser. Explicit adopted weights can replace the nominal value of any recognized element, including one without a standard atomic weight, but doing so does not identify an isotope or validate the supplied data. A formula with an unsupported label receives an error. The calculator also does not check oxidation states, reaction balance, chemical stability or whether a written composition corresponds to an isolable substance.
Why can mass percentages or rounded outputs differ from another calculator?
Calculators can use different atomic-weight editions, nominal values, isotope assumptions or rounding policies. This report keeps its adopted weights visible and sums their decimal contributions before rounding the display. Element percentages use that unrounded sum and are then rounded independently, so their displayed total can differ slightly from one hundred percent. Increasing display significant figures changes presentation rather than the underlying adopted weights, their variability or the precision of a measured sample.
How are grams, moles and entity counts connected?
The sample converter divides mass by the adopted molar mass to find amount, or multiplies amount by it to find mass. It then uses the defined Avogadro constant to estimate the number of molecules or formula units and the total number of atoms. Unit conversions are explicit, and the unrounded adopted mass is used throughout. The exact definition of the Avogadro constant does not remove uncertainty in a measured sample or natural isotope composition.
What do copying, sharing, importing and printing retain?
Complete text and CSV reports retain every element contribution and local group expansion beyond the current visual page. Sample CSV rows include exact rational certificates for arithmetic on the adopted input decimals. Shared links contain only active sample values and active adopted overrides; unused editing buffers stay local. Local text import accepts one complete formula and leaves existing inputs intact when invalid or oversized. Printing follows the current visible element and group pages, with explicit notices replacing expressions too long for the sheet.
About This Tool

About this Molar Mass Calculator

The Molar Mass Calculator connects a chemical composition to a transparent nominal mass estimate. Its starting point is the formula grammar: case-sensitive element symbols, whole-number subscripts, matched nested groups and explicitly separated adduct parts. Parsing establishes the atom counts before any weight is applied. This makes a malformed bracket, a reaction coefficient or an unsupported charge label a visible input problem rather than a source of plausible but incorrect arithmetic.

The default numerical basis is the CIAAW Abridged Standard Atomic Weights 2024 table. Published nominal decimals are retained as strings and summed with exact decimal arithmetic inside the adopted model. The library also recognizes elements for which the table gives no standard atomic weight. Those entries require an explicit adopted value, and every active replacement is identified in the report. Quoted reference uncertainties, natural isotope variability and measurement uncertainty are not silently converted into a fabricated precision claim. Optional sample conversions keep their unit choices and use the unrounded adopted sum.

The result distinguishes the written formula, the aggregate Hill-order composition and the simplest whole-number atom ratio. These representations help inspect counts without claiming structural identity or changing the original species used for molar mass. Element cards, group expansions and complete exports support a reviewable explanation on a small screen. Shared settings contain active numerical choices, while visual page positions remain local browsing choices. The tool is intended for ordinary educational composition checks and explicitly adopted-data comparisons; it does not balance reactions, identify isotopes, calculate isotope patterns, infer purity or certify a physical sample.

Editorial Transparency

Who maintains this page

Ownership and review

Written and maintained by the Toolarithm editorial team. No review date is shown without a maintained editorial record. No independent professional review is claimed.

Methodology

The method identifies the governing relationship, units, significant assumptions, and educational scope. SI terminology is checked against the BIPM reference.

Read the editorial methodology

Dates and sources

Review dates change only after a substantive method or content check.

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