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 calculate molar mass in grams per mole.
Inputs explained Result checks Example values Runs in your browser
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.
What people use it for
Find molar mass for common formulas.
Check element counts in parentheses.
Estimate mass percentage by element.
Use the result in the Molarity Calculator.
Quick examples
Water
H2OAbout 18.015 g/mol: two H atoms plus one O atom
Glucose
C6H12O6About 180.156 g/mol for the full formula unit
Calcium hydroxide
Ca(OH)2About 74.092 g/mol, with the OH group counted twice
Copper sulfate pentahydrate
CuSO4.5H2OHydrate waters included in the total molar mass
Need the guide or a nearby tool?
Need a slower walkthrough, a related calculator, or the full library? These links keep you close to the task you started.
- How to use the Molecular Weight Calculator See slower examples, input meanings, formula notes, result limits, and mistakes to avoid.
- School & Study Browse related calculators and utilities in the same category.
- Calculator and utility guides Find more guides that use real tool inputs and example numbers.
- All free tools Search every live tool, converter, calculator, AI helper, and browser utility.
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 measurements, amounts, units, or options 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. For H2O, it adds two hydrogen atoms and one oxygen atom for about 18.015 g/mol. The examples on the page are there so you can compare your inputs with a worked example before copying the answer.
What do the main Molecular Weight Calculator inputs mean?
Chemical formula: element symbols and counts, such as H2O, C6H12O6, Ca(OH)2, or CuSO4.5H2O. Subscripts: the numbers after element symbols or parentheses that multiply atom counts. Dot hydrates: formula parts separated by a period, where a leading number multiplies the following hydrate group. Mass share: the percentage of the total molar mass contributed by each element.
How should I read the Molecular Weight Calculator answer?
Read the headline answer, then check the supporting lines and examples to understand how the calculator got there. If one input changes, rerun the tool and compare the new answer instead of guessing.
What should I double-check before trusting the answer?
The atomic-weight table is rounded and supports common classroom elements. Isotopes, charges, exact masses, structural formulas, and unsupported elements need reference data. Also check the unit, scale, mode, and result limit because small input changes can change the answer.
Why does capitalization matter in a formula?
Element symbols use one capital letter and sometimes one lowercase letter. CO means carbon and oxygen, but Co means cobalt. The calculator reads capitalization as part of the chemistry symbol.
Is molecular weight the same as molar mass?
For classroom formula work, people often use the terms together. The calculator returns grams per mole, so the result is the molar mass you can use in stoichiometry or in the Molarity Calculator.
How are parentheses handled?
A number after parentheses multiplies everything inside the group. Ca(OH)2 counts one calcium, two oxygens, and two hydrogens before the atomic weights are added.
Can I enter hydrates like CuSO4.5H2O?
Yes. Use a period between the main formula and hydrate part. The leading 5 multiplies the H2O group, so the calculator includes five waters of hydration in the total.
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.
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