Molecular Weight Calculator.

Formula or algorithm and variables.

Equation, units, and population

relative molecular mass = Σ(atomic weight × atom count). Element symbols are case-sensitive. Parenthetical groups and whole-number subscripts are expanded before atomic weights are summed. This page names the equation rather than presenting an unexplained score. Check that every value uses the displayed unit and that you belong to the population for which the method is described. The calculation retains full precision internally and rounds only the visible result. A reproducible estimate should let another reader use the same inputs and reach the same arithmetic answer, while still recognizing that mathematical reproducibility does not prove medical suitability.

Worked example

H₂O contains two hydrogen atoms and one oxygen atom: 2 × 1.008 + 15.999 = 18.015. The relative molecular mass is 18.015 and the corresponding molar mass is approximately 18.015 g/mol. Work through the example by writing the equation, substituting each labeled input, and preserving units at every step. The example demonstrates arithmetic only; it is not a recommended body measurement, intake, exercise level, laboratory value, or date. Replace every example input with the values from the situation being considered, and retain those inputs with any result you copy. Small differences can arise from rounding, equation versions, atomic-weight conventions, or date boundaries.

Interpreting the estimate

Relative molecular mass is dimensionless; the numerically corresponding molar mass is shown in g/mol for a mole of entities with the entered formula. Health calculations compress complex biology into a few inputs, so the result should be read as context rather than a verdict. Do not compare two people as though the higher or lower number is automatically better. Look for changes over time only when the method, units, and conditions are consistent. If a result conflicts with symptoms, a laboratory report, a clinician’s instructions, or a validated measurement, rely on the appropriate professional evidence rather than this calculator.

Validation and edge cases

The formula must use supported element symbols, balanced parentheses, positive whole-number subscripts, and no unsupported charge, hydrate, or punctuation notation. Blank, malformed, nonfinite, and out-of-domain inputs fail explicitly without producing NaN or infinity. The bounds prevent obviously implausible values from being mistaken for meaningful answers, but passing a range check does not make an input medically correct. Recheck dates, decimal separators, unit conversions, coefficient choices, and whether a laboratory value uses the expected assay and unit. Contact a qualified professional when a result could affect treatment, medication, pregnancy care, nutrition therapy, or exercise safety.

Limitations and responsible use

Displayed standard atomic weights are conventional rounded values and isotopic composition can change an exact mass. Hydrates separated by dots, charges, isotopes, and structural formulas are outside this parser. This chemistry calculation identifies formula mass only. It does not verify a substance identity, purity, concentration, reaction, or laboratory safety. FigureNest processes these inputs locally in the browser and does not send them to a calculation service. The page does not create a medical record, assess symptoms, or know personal history. Avoid using estimates to shame a body, pursue unsafe restriction, delay care, determine legal fitness, or replace contraception. Authoritative source links are provided so readers can check the equation version and current guidance before making a consequential decision.

Check assumptions and sources.

Displayed standard atomic weights are conventional rounded values and isotopic composition can change an exact mass. Hydrates separated by dots, charges, isotopes, and structural formulas are outside this parser.

IUPAC Gold Book — Relative Molecular Mass

NIST Atomic Weights and Isotopic Compositions