Conversion Calculators

Molecular Weight Calculator

Use this molecular weight calculator to convert compatible units or encoded values for molecular weight.

Primary answer: Molar mass
Inputs to verify: Chemical formula
Use type: Use as an estimate that depends on assumptions.
Keyword intent: molecular weight calculator

Result

Result reflects the current submitted inputs.

Risk B
Reviewed 2026-05-26
4 sources

Molar mass18.015 g/mol

Relative formula mass18.015

Total atoms3 atoms

Element countsH:2, O:1

Parsed formulaH2O

Breakdown

H: 11.1907%
O: 88.8093%

Atomic weights use an abridged standard atomic-weight table suitable for natural terrestrial samples.
Synthetic and radioactive elements use conventional mass-number style values where standard atomic weights are unavailable.
The parser supports integer subscripts, nested parentheses/brackets/braces, and hydrate dot notation.
Isotope-specific exact masses, charged species, structural formulas, and reaction balancing are out of scope.
Intermediate sums are not rounded; final raw masses are rounded to 6 decimals.

Accuracy notes

Risk level: B
Reviewed: 2026-05-26
Sources: 4
Primary result: Molar mass

Formula logic is kept in a pure calculator module with fixtures, source notes, and page-visible assumptions.

What the result means

Use Molar mass as the headline answer for molecular weight. Formula mass expressed as grams per mole. Read the converted value first, then verify the source unit, target unit, and factor before reusing the number. Use relative formula mass, total atoms, and element counts to explain why molar mass moved when an input changed. Keep the original value next to the converted value when using it in a workflow. Check source unit, target unit, dimension compatibility, exchange or conversion rate, and rounding precision before treating the result as final.

Molar massFormula mass expressed as grams per mole.

Relative formula massDimensionless relative formula mass using the same atomic-weight sum.

Total atomsTotal atom count after all subscripts and group multipliers.

Element countsElement counts in first-appearance order.

Use the result this way

Start with Molar mass, then use supporting outputs only to explain the primary answer.
Verify chemical formula before copying the result.
Check units, ranges, and rounding before comparing outputs.
Keep the original value next to the converted value when using it in a workflow.

User job

How to use this calculator

Use Molecular Weight Calculator when you need molar mass, then use relative formula mass and total atoms to check the context for unit checks, engineering notes, recipes, travel, shopping, and measurement cleanup.

Best for

Converting compatible units
Auditing the factor used for a repeated conversion
Reviewing a default example before entering your own chemical formula.

Check before relying

Make sure the source and target units measure the same kind of quantity.
Atomic weights use an abridged standard atomic-weight table suitable for natural terrestrial samples.
Synthetic and radioactive elements use conventional mass-number style values where standard atomic weights are unavailable.
Source context: International Union of Pure and Applied Chemistry, reviewed 2026-05-26.

Next useful step

Weight CalculatorUse next when the body metric task needs mass instead of molar mass.
Density CalculatorUse next when the unit conversion task needs mass instead of molar mass.
Lean Body Mass CalculatorUse next when the body metric task needs estimated lean body mass instead of molar mass.

Formula

Molar mass is the sum of each element's atomic weight multiplied by its count in the formula. Key assumptions: Atomic weights use an abridged standard atomic-weight table suitable for natural terrestrial samples. Synthetic and radioactive elements use conventional mass-number style values where standard atomic weights are unavailable. The parser supports integer subscripts, nested parentheses/brackets/braces, and hydrate dot notation.

Molar mass is the sum of each element's atomic weight multiplied by its count in the formula.
Atomic weights use an abridged standard atomic-weight table suitable for natural terrestrial samples.
Synthetic and radioactive elements use conventional mass-number style values where standard atomic weights are unavailable.
Primary source context: International Union of Pure and Applied Chemistry.

Inputs

Enter chemical formula for unit checks, engineering notes, recipes, travel, and measurement cleanup. Chemical formula: Supports element symbols, integer subscripts, (), [], {}, and hydrate dot notation such as CuSO4·5H2O.

Chemical formulaSupports element symbols, integer subscripts, (), [], {}, and hydrate dot notation such as CuSO4·5H2O.

Example

Using the default inputs, Molecular Weight Calculator returns molar mass of 18.015 g/mol. Adjust chemical formula to match your own scenario.

FAQ

How is molar mass calculated here?

Molar mass is the sum of each element's atomic weight multiplied by its count in the formula. The first assumption to check is: Atomic weights use an abridged standard atomic-weight table suitable for natural terrestrial samples.

What does Molar mass mean for molecular weight?

Read the converted value first, then verify the source unit, target unit, and factor before reusing the number. Secondary values such as relative formula mass, total atoms, and element counts are there to explain the primary answer, not to replace it.

What should I enter for Chemical formula?

Supports element symbols, integer subscripts, (), [], {}, and hydrate dot notation such as CuSO4·5H2O. Check the label, unit, and allowed range before comparing outputs.

What can make the molecular weight answer change?

The answer can change when inputs, units, rounding, or source assumptions change. Compare source unit, target unit, dimension compatibility, exchange or conversion rate, and rounding precision.

Why does the molecular weight example show 18.015 g/mol for molar mass?

The default inputs produce 18.015 g/mol for molar mass. Treat that as a format and scale check, then replace every default value with your own inputs.

How do I avoid a molecular weight unit-direction mistake?

Keep the original value beside the converted value, confirm both units measure the same quantity, and check whether rounding is acceptable for the task.

Sources

Last reviewed: 2026-05-26

Reviewed 2026-05-26
IUPAC Gold Book - relative molecular massInternational Union of Pure and Applied Chemistry. Definition context for summing relative atomic masses by chemical formula.
Scope
Terminology for relative molecular mass and molecular-weight-style calculations.
Supports
Definition context for summing relative atomic masses by chemical formula.
Reviewed 2026-05-26
Chemistry LibreTexts - Molar MassChemistry LibreTexts. Use of the atomic-weight sum as molar mass in grams per mole.
Scope
Educational chemistry reference for molar mass and formula-mass arithmetic.
Supports
Use of the atomic-weight sum as molar mass in grams per mole.
Reviewed 2026-05-26
CIAAW Standard Atomic WeightsIUPAC Commission on Isotopic Abundances and Atomic Weights. Atomic-weight source hierarchy and annual review cadence.
Scope
Standard atomic weights and interval/abridged values for the elements.
Supports
Atomic-weight source hierarchy and annual review cadence.
Reviewed 2026-05-26
NIST Chemistry WebBook - D-GlucoseNational Institute of Standards and Technology. Independent comparison for representative molecular-weight fixture.
Scope
Authoritative formula and molecular-weight comparison record for a common compound.
Supports
Independent comparison for representative molecular-weight fixture.

Disclaimer

This calculator is an educational estimate based on the inputs and assumptions shown on the page.

Molecular Weight Calculator