Your result
Click Calculate
Enter your values, then click Calculate result.How this calculator helps
Calculate molecular weight and molar mass from a chemical formula, then inspect each element’s atom count, mass contribution and percentage by mass. Enter formulas such as H2O, C6H12O6, Ca(OH)2 or CuSO4·5H2O and press Calculate. The tool keeps this page focused on formula-based molecular-weight intent rather than mixing in separate protein, DNA, solution-preparation or stoichiometry calculators.
How to use it
- 1
Enter a case-sensitive chemical formula using standard element symbols, for example H2O or NaCl.
- 2
Use integer subscripts after an element or group. Parenthesized groups such as Ca(OH)2 and hydrate notation such as CuSO4·5H2O are supported.
- 3
Press Calculate. The result reports molar mass in g/mol, the numerically equivalent average molecular mass in daltons, and an element-by-element breakdown.
- 4
Check each element’s atom count, atomic weight, mass contribution and percentage by mass. Recheck the formula and hydration state before using the result in later chemistry work.
Formula and methodology
Molecular weight = Σ(standard atomic weight × atom count). Mass % = element contribution ÷ total molecular weight × 100.
The calculator applies the disclosed heuristic to values entered on this device. It does not load private admissions data or claim to reproduce an institution's review process.
Worked calculation example
H2O gives about 18.015 g/mol: two hydrogen atoms plus one oxygen atom. The result also shows each element’s contribution and mass percentage.
How to interpret your result
Calculate molecular weight and molar mass from a chemical formula with grouped atoms, hydrates, element breakdown and mass percentages. Read the main result together with the supporting values rather than treating one number as a guarantee. The disclosed method is: Molecular weight = Σ(standard atomic weight × atom count). Mass % = element contribution ÷ total molecular weight × 100.
Input guide
Enter a case-sensitive chemical formula using standard element symbols, for example H2O or NaCl.
Use integer subscripts after an element or group. Parenthesized groups such as Ca(OH)2 and hydrate notation such as CuSO4·5H2O are supported.
Press Calculate. The result reports molar mass in g/mol, the numerically equivalent average molecular mass in daltons, and an element-by-element breakdown.
Scenario comparison
| Scenario | What it demonstrates |
|---|---|
| Worked baseline | H2O gives about 18.015 g/mol: two hydrogen atoms plus one oxygen atom. The result also shows each element’s contribution and mass percentage. |
| Molecular weight, molecular mass and molar mass check | For a specified composition, the calculator reports the average formula mass from standard atomic weights. The numerical value expressed as molecular mass in Da is the same numerical value commonly used for molar mass in g/mol, but the quantities and units describe different scales. Ionic compounds are often described by formula mass rather than the mass of a discrete molecule. |
| Formula parsing and grouped atoms stress test | Subscripts multiply the element immediately before them, while a number after parentheses multiplies every atom in that group. For Ca(OH)2, the parser counts one calcium, two oxygen atoms and two hydrogen atoms. Nested parentheses are accepted when the notation remains unambiguous and every element symbol uses correct capitalization. |
Common mistakes to avoid
- Ignoring molecular weight, molecular mass and molar mass: For a specified composition, the calculator reports the average formula mass from standard atomic weights. The numerical value expressed as molecular mass in Da is the same numerical value commonly used for molar mass in g/mol, but the quantities and units describe different scales. Ionic compounds are often described by formula mass rather than the mass of a discrete molecule.
- Overlooking formula parsing and grouped atoms: Subscripts multiply the element immediately before them, while a number after parentheses multiplies every atom in that group. For Ca(OH)2, the parser counts one calcium, two oxygen atoms and two hydrogen atoms. Nested parentheses are accepted when the notation remains unambiguous and every element symbol uses correct capitalization.
- Failing to test hydrates need the water multiplier: A hydrate is not equivalent to its anhydrous salt. CuSO4·5H2O includes five waters of hydration, so leaving off ·5H2O changes the calculated molar mass substantially. The calculator accepts a middle dot and normalizes it for parsing. Verify the exact chemical form on the reagent label or in the problem statement.
Check the formula, weights and rounding method published by the relevant institution before using the result officially.
Search intent and calculator coverage
Molecular mass is the sum of each element's atomic mass multiplied by its atom count. The displayed result is only as accurate as the entered atomic masses and parsed formula.
Related questions this calculator covers
- molecular mass from atomic masses and atom counts
- molar mass calculation for a simple compound
- sum element contributions from a formula
Worked scenarios
| Scenario | What it shows |
|---|---|
| H₂O | two hydrogen atoms plus one oxygen atom |
| CO₂ | one carbon plus two oxygen atoms |
| Nested parentheses are supported; hydrates, charges, isotopes and lab-specific conventions need separate verification |
Common mistakes to avoid
- Omitting subscripts
- Confusing molecular mass with a sample's total mass
- Using rounded atomic masses for precision work
Compare the parsed element counts with the original chemical formula and verify masses against a current periodic table.
For laboratory or regulated work, follow the required atomic-weight convention and verify with a chemistry reference.What can affect the result?
Molecular weight, molecular mass and molar mass
For a specified composition, the calculator reports the average formula mass from standard atomic weights. The numerical value expressed as molecular mass in Da is the same numerical value commonly used for molar mass in g/mol, but the quantities and units describe different scales. Ionic compounds are often described by formula mass rather than the mass of a discrete molecule.
Formula parsing and grouped atoms
Subscripts multiply the element immediately before them, while a number after parentheses multiplies every atom in that group. For Ca(OH)2, the parser counts one calcium, two oxygen atoms and two hydrogen atoms. Nested parentheses are accepted when the notation remains unambiguous and every element symbol uses correct capitalization.
Hydrates need the water multiplier
A hydrate is not equivalent to its anhydrous salt. CuSO4·5H2O includes five waters of hydration, so leaving off ·5H2O changes the calculated molar mass substantially. The calculator accepts a middle dot and normalizes it for parsing. Verify the exact chemical form on the reagent label or in the problem statement.
Atomic-weight basis and precision
The calculator uses conventional abridged standard atomic-weight values for supported naturally occurring elements, consistent with the kind of IUPAC values used by established chemistry calculators. Standard atomic weights describe terrestrial isotope mixtures and are not exact monoisotopic masses. Display precision does not remove uncertainty in the underlying atomic-weight data.
Percent composition
Mass percent for an element equals that element’s total mass contribution divided by the compound’s total calculated mass, multiplied by 100. The displayed element rows make that arithmetic auditable instead of returning only one total.
What this calculator intentionally does not do
This page does not balance reactions, infer a compound name, calculate solution molarity, convert laboratory quantities, estimate protein or nucleic-acid sequence mass, or calculate exact isotope-specific mass. Those are different tasks with different inputs and should not be hidden behind a molecular-weight result.
Privacy and browser processing
Values entered on this page are processed in the current browser session. SolvePilot does not require an account and does not receive the values entered into the calculator. Refreshing or closing the page clears the working values unless the browser itself restores a previous session. Avoid entering identifying or account information because the calculation needs summary values only.
Accuracy and verification
Accuracy depends first on input quality. Confirm definitions, scales, dates and source information before entering a value. Keep an independent record of any result used for planning because this page does not create an official statement or retain a calculation history.
Limits of this estimate
This calculator is for average formula mass from supported chemical formulas. It does not calculate monoisotopic or exact mass, isotope-labelled compounds, polymers with molecular-weight distributions, reaction products, solution concentration, purity corrections or unknown mixtures. Element symbols are case-sensitive. Standard atomic weights can vary with isotopic composition, and highly precise analytical work should use the current IUPAC/CIAAW value and uncertainty appropriate to the sample.
Sources and review information
Frequently asked questions
How do I calculate molecular weight from a chemical formula?＋
Count the atoms of each element, multiply each count by that element’s standard atomic weight, and add the contributions. The calculator performs those steps and shows the contribution of every detected element.
Is molecular weight the same as molar mass?＋
They are closely related and have the same numerical value for a specified composition when average atomic weights are used, but their units and physical meanings differ. Molecular mass is commonly expressed in daltons (Da), while molar mass is expressed in grams per mole (g/mol).
Does the calculator support parentheses such as Ca(OH)2?＋
Yes. A multiplier after parentheses applies to every element inside the group, so Ca(OH)2 is parsed as Ca1, O2 and H2.
Can I calculate hydrates such as CuSO4·5H2O?＋
Yes. Use the hydrate dot and multiplier so the waters of hydration are included. Omitting the hydrate portion calculates the anhydrous compound instead.
Why can another molecular weight calculator give a slightly different answer?＋
Differences usually come from atomic-weight tables, rounding, isotope assumptions or formula interpretation. For high-precision work, verify the current IUPAC/CIAAW atomic-weight data and the exact chemical form.
Does this calculate exact or monoisotopic mass?＋
No. It uses average standard atomic weights. Exact monoisotopic mass requires isotope-specific masses and is a separate calculation.
Does SolvePilot upload or save my chemical formula?＋
No account is required and the calculation runs in the browser. The formula is used to produce the displayed result in the current session.