Molar Mass Calculator
Calculate Molecular Weight From Chemical Formulas
Use the Molar Mass Calculator to find the mass of a chemical formula in grams per mole. See every element, atom count and contribution, including examples with brackets and parentheses.
Enter a chemical formula
Editable inputsImportant β chemical symbols are case-sensitive: The first letter must be uppercase. If there is a second letter, it must be lowercase: H, O, Fe, Na, Cl. Write FeβOβ, not fe2o3 or FE2O3.
Results & explanation
Your calculated result will appear here.
Results use a fixed approximate atomic-weight table. Check substance identity, significant figures and measurement assumptions before practical use.
How to Calculate Molar Mass: Step-by-Step Guide
Molar mass joins two ideas: a chemical formula specifies how many atoms are in one formula unit, and each element has an atomic mass reference value. Multiply each atomic mass by the number of its atoms and add the contributions. The result, in grams per mole, is the mass of one mole of that compound.
Step 1: Read the element symbols accurately
Symbols must start with an uppercase letter; the second letter of a two-letter symbol is lowercase. H is hydrogen, O is oxygen, Fe is iron, and Ca is calcium. The calculator does not silently reinterpret improperly capitalized symbols.
Step 2: Expand subscripts and brackets
HβO contains two H atoms and one O atom. Ca(OH)β contains one Ca, two O and two H atoms. The group multiplier outside the parentheses applies to everything within it.
Step 3: Sum the weighted atomic masses
For water, calculate (2 Γ 1.008) + (1 Γ 15.999) = 18.015 g/mol. For a larger compound, keep adding one contribution per element until the complete formula is accounted for.
Worked Examples: Molar Mass Calculations
Use any button to load that example into the calculator above on this page. Its calculation and explanation will update automatically.
How do I solve HβO: water, the basic formula?
Select this preset to inspect the given chemical formula or equation, the intermediate calculations and the final numerical result. Try changing one input afterward and observe which step changes.
How do I solve Ca(OH)β: parentheses?
Select this preset to inspect the given chemical formula or equation, the intermediate calculations and the final numerical result. Try changing one input afterward and observe which step changes.
How do I solve Alβ(SOβ)β: nested counting?
Select this preset to inspect the given chemical formula or equation, the intermediate calculations and the final numerical result. Try changing one input afterward and observe which step changes.
Learn More About Molar Mass and Atomic Weights
For equation-based exercises, first learn how to balance chemical equations, then practice the balancing method. Accurate coefficients are essential whenever you calculate product yields from a reaction.
Methodology
The tool first parses the formula and multiplies the atoms within each bracketed group by the following subscript. A hydrate such as CuSOβΒ·5HβO includes five water units, so the 5 multiplies both H and O in the hydrate part. A subscript of 1 is implied where no number appears.
For every element, the contribution is element atom count Γ atomic-weight value. The total molar mass is M = Ξ£(nα΅’ Γ Aα΅’) in g/mol. For water, HβO, the calculation is 2 Γ 1.008 + 15.999 = 18.015 g/mol using the calculator’s rounded reference values.
The atomic-weight values are a fixed teaching table in this JavaScript. They are approximate and not fetched live; for naturally variable elements, an atomic-weight interval or a sample-specific isotopic composition can produce a different answer. The calculator uses representative mass numbers for certain radioactive elements without standard atomic weights and marks those answers approximate.
Assumptions and Limitations
Element-symbol capitalization is enforced; use Ca, not CA. Values are based on rounded atomic weights embedded in the source code, not a live database. Isotopic enrichment, naturally variable atomic-weight intervals, radionuclides and advanced coordination notations can require more specialized data or parsing. The result describes the entered formula, not substance purity or concentration.
Questions People Ask
Open any question for a detailed explanation, an example, and the underlying chemical principle.
What is molar mass, and how is it different from molecular mass?
Molar mass is the mass of one mole of a chemical substance, normally reported in grams per mole (g/mol). The molar mass of water is about 18.015 g/mol. That means a sample containing one mole of water molecules has a mass of approximately 18.015 g. Molecular mass usually refers to the mass of one molecule in atomic mass units (u), whereas molar mass is an amount-of-substance conversion factor.
For compounds such as NaCl that form an ionic lattice rather than discrete molecules, we still calculate the molar mass of the formula unit. The numerical values are related, but the physical descriptions and units are different.
How do I calculate molar mass from a chemical formula step by step?
First, write the formula with valid element symbols, for example HβO. Second, count the atoms: two hydrogens and one oxygen. Third, find the atomic masses from the reference values being used. Using approximate values H = 1.008 and O = 15.999, multiply to get 2 Γ 1.008 = 2.016 for hydrogen and 1 Γ 15.999 = 15.999 for oxygen. Finally add 2.016 + 15.999 = 18.015 g/mol.
The process is the same for more complex formulas, except you must multiply any bracketed group by its outside subscript and include any hydrate water groups.
How do parentheses change the calculated molecular weight?
Parentheses multiply the entire group. For Ca(OH)β, the single Ca contributes one calcium atom. The β applies to both O and H in the OH group, giving two oxygen and two hydrogen atoms. The formula therefore has CaβOβHβ, not CaβOβHβ.
The calculator expands the group and shows separate mass contributions. Working this way helps prevent the common error of multiplying only the final element in a bracket. You can inspect this expansion in the loaded example and verify the approximate molar mass of 74.092 g/mol using the selected atomic mass table.
How is molar mass related to grams, moles and stoichiometry?
Molar mass is the bridge between a measured mass and an amount of substance. The two main conversions are moles = grams Γ· molar mass and grams = moles Γ molar mass. For example, about 36.03 g of water corresponds to approximately two moles because 36.03 Γ· 18.015 β 2.
Once the quantities are in moles, the coefficients in a balanced chemical reaction allow you to relate reactants and products. This is why molar mass is an essential preliminary calculation for stoichiometry, theoretical yield and limiting-reactant problems.
Why are some atomic weights decimal values rather than whole numbers?
Periodic-table atomic weights for many elements are averages associated with isotope masses and abundances. For instance, the approximate atomic mass of chlorine is 35.45, not exactly the mass number of a single chlorine nucleus. It reflects naturally occurring isotopic composition rather than fractional protons or neutrons.
The values here are convenient classroom approximations. For some radioactive or synthetic elements with no standard atomic weight, a representative isotope mass number is substituted and marked as approximate. For measurements requiring traceable laboratory precision, verify the element mass values and isotopic composition appropriate to your sample.
Sources and Further Reading
The calculation algorithms and educational explanations are implemented directly for CalcTypes; the following sources support chemistry definitions, chemical symbols and atomic-weight conventions. These references do not endorse this website or its particular algorithm.
- OpenStax Chemistry 2e β Writing and Balancing Chemical Equations β
- CIAAW β Standard Atomic Weights β
- ElementLookup β Balancing Equations Lesson β
- ElementLookup β Relative Atomic Mass Lesson β
The molar-mass data inside this JavaScript is a fixed rounded teaching table, not a full copy of the latest CIAAW standard atomic-weight table. Some standard weights are given as intervals; results may differ from high-precision reference calculations. The Avogadro constant used in mole conversions is 6.02214076 Γ 10Β²Β³ molβ»ΒΉ.
Important Disclaimer β Educational Use Only
Educational approximation only. Molar masses are calculated from a fixed table of rounded atomic-weight values. Isotopic composition, radioactive elements, chemical composition, hydration state and measurement precision can change the appropriate mass to use. A mathematically correct sum does not confirm the identity, purity or composition of a material.
Verify before real-world use. Do not use these outputs as the sole basis for preparing reagents, dosing chemicals, manufacturing, clinical work, regulated analysis or safety-critical procedures. Verify the chemical formula, reference atomic masses and sample specification against current authoritative data and relevant laboratory procedures, preferably with a qualified chemistry professional.
CalcTypes provides general educational calculations and explanations, not a guarantee of accuracy, safety, suitability or professional certification. Users remain responsible for checking inputs and interpreting results for their own circumstances.