H2O
- Atoms counted
- 3
- Elements
- H, O
- Largest mass share
- O
Composition: H 2 (11.190674438%), O 1 (88.809325562%)
Molecular Weight Calculator
Use this free molecular weight calculator to parse common chemical formulas and estimate molar mass in grams per mole.
Research-backed assumptions Formula steps Examples included Private in-browser use
Formula steps
- Parse element symbols, subscripts, and parentheses in the formula.
- Multiply each element count by its rounded atomic weight.
- Add the element masses to estimate molar mass.
How to use the molecular weight calculator
- Enter a chemical formula such as H2O, C6H12O6, or Ca(OH)2.
- Press Calculate molecular weight to see estimated g/mol and element composition.
- Use dot hydrate notation with a period, such as CuSO4.5H2O.
- Use isotope-specific references when exact mass matters.
Common uses
Find molar mass for common formulas.
Check element counts in parentheses.
Estimate mass percentage by element.
Use the result in the Molarity Calculator.
Examples
About 18.015 g/mol
About 180.156 g/mol
Parentheses parsed
Frequently asked questions
Plain-language answers about when to use the tool, what it does with your inputs, what to double-check, and how privacy works.
When should I use the Molecular Weight Calculator?
Use it when your task matches one of these common needs: Find molar mass for common formulas. Check element counts in parentheses. It works best when you already know the values, dates, units, or settings the page asks for.
What is the Molecular Weight Calculator doing with my inputs?
In plain language: The calculator parses element symbols, subscripts, parentheses, and dot hydrate parts, then adds each element count times its rounded atomic weight. The examples on the page are there so you can compare your inputs with a filled-out calculation before copying the answer.
What should I double-check before trusting the answer?
The atomic-weight table is rounded and supports common classroom elements. Isotopes, charges, exact masses, and unsupported elements need reference data. Also check that you used the right unit, date, scale, or mode because small input changes can change the result.
Does the site save what I enter?
No. The calculator runs in your browser tab. Your recent answers stay only on the page while you use it, and they are not sent to a server.
Related tools
Molarity Calculator Calculate molarity from moles and liters or from grams, molar mass, and liters. Open Scientific Calculator A free scientific calculator for trig, logs, roots, powers, and constants. Open Conversion Calculator Convert length, mass, volume, and temperature units with clear formula steps. Open