CalcaTools

Molecular Weight Calculator | Molar Mass in g/mol & Moles

Computes the molar mass of any chemical formula. Enter a formula like H2O or C6H12O6, and the tool sums the atomic masses of every element present using standard atomic weights, returning the molar mass in g/mol, and converts between grams and moles for the given mass.

Last updated: June 2026 · Free · No sign-up required

Results

Enter values above and click Calculate to see your result instantly.

Quick reference

ElementAtomic mass (g/mol)
H1.008
C12.011
N14.007
O15.999
Na / Cl22.990 / 35.45

apps Small jobs, done in one click

Everyday calculators are the workshop drawer of the site — quick utilities for the moments when you need a number now and a phone calculator won't cut it. Age, date difference, GPA, fuel cost, time-to-decimal, password strength — pick a tool and you're one click from your answer.

speed Loads in under a second

Every tool is plain HTML + JavaScript with the calculation logic compiled in. No spinner, no "verifying browser" splash, no five-second wait while ads load. Hit the page, fill the form, get the answer. Slow tools waste your time and ours.

devices Works on every device

Responsive design tested down to a 320px-wide phone screen. The input fields use native number/date keyboards on iOS and Android, the calculate button is thumb-sized, and the result still reads big and bold on the smallest screen. No app to download, ever.

sentiment_satisfied No funny business

No newsletter pop-ups, no "create an account to see the answer", no fake countdown, no fake stock counter, no upsell. Two ad slots per page (clearly labelled as Advertisement) keep the site free — that's the whole business model.

Interpretation guide

CompoundMolar mass
H₂O18.02 g/mol
CO₂44.01 g/mol
NaCl58.44 g/mol
C₆H₁₂O₆ (glucose)180.16 g/mol

lightbulb Worked example

Let's say you are using the Molecular Weight Calculator. Computes the molar mass of any chemical formula. Enter a formula like H2O or C6H12O6, and the tool sums the atomic masses of every element present using standard atomic weights, returning the molar Enter the values that match your situation into the input fields and press calculate — using realistic numbers makes the result directly useful for you.

Result: The calculator instantly applies the formula Molar mass = sum over atoms of (atomic mass x count); moles = mass (g) / molar mass (g/mol) and returns the result with appropriate precision.

What this means: Read the result in the context of what you are measuring. The step-by-step breakdown lets you confirm the math and understand which input most affects the outcome.

Formula & methodology

Formula: Molar mass = sum over atoms of (atomic mass x count); moles = mass (g) / molar mass (g/mol)

The Molecular Weight Calculator is built on a well-established calculation method. It uses the formula Molar mass = sum over atoms of (atomic mass x count); moles = mass (g) / molar mass (g/mol) to turn your inputs into a reliable result. Computes the molar mass of any chemical formula. Enter a formula like H2O or C6H12O6, and the tool sums the atomic masses of every element present using standard atomic weights, returning the molar mass in g/mol, and The steps are shown on the page so you can follow the reasoning from input to output.

How molecular weight is calculated

Molecular weight (molar mass) is the sum of the atomic masses of every atom in the formula, in grams per mole.

Example: H₂O

2 hydrogen (2 x 1.008) + 1 oxygen (15.999) = 2.016 + 15.999 = 18.02 g/mol.

Example: glucose C₆H₁₂O₆

6 x 12.011 + 12 x 1.008 + 6 x 15.999 = 72.066 + 12.096 + 95.994 = 180.16 g/mol.

Once you have the molar mass, convert any sample: moles = mass / molar mass. So 36 g of water is 36 / 18.02 = 2.0 mol.

What is the Molecular Weight Calculator?

The Molecular Weight Calculator is a free, browser-based everyday calculator tool that helps you Computes the molar mass of any chemical formula. Enter a formula like H2O or C6H12O6, and the tool sums the atomic masses of every element present using standar. Instead of working through the math by hand or in a spreadsheet, you enter your values and the calculator returns an accurate result instantly — while still showing the formula and the steps so you can verify the reasoning. It is designed for quick everyday use: no sign-up, no installation, and everything runs locally in your browser for complete privacy.

How to use the Molecular Weight Calculator

  1. Enter the required values into the input fields.
  2. Press the calculate button — the result appears immediately, updated live as you change any value.
  3. Read the step-by-step breakdown below the result to see exactly how the calculation was performed.
  4. Use the interpretation guide to understand what the result means for your situation, and try different inputs to see how they change the outcome.

How to use the Molecular Weight Calculator

Enter the chemical formula using element symbols and subscripts, such as H2O for water or C6H12O6 for glucose, and press calculate. The tool looks up each element's atomic mass from the periodic table, multiplies it by the subscript, and sums the results to give the molar mass in grams per mole. For hydrated compounds, include the water of crystallization — CuSO4·5H2O — and the tool accounts for the five water molecules.

Interpreting your result

The molar mass tells you the mass of one mole of the substance — Avogadro's number of molecules. It converts between mass and moles with moles = mass (g) ÷ molar mass (g/mol), which is the first step in nearly every stoichiometry calculation. For example, glucose has a molar mass of about 180.16 g/mol, so 36 grams of glucose is about 0.2 moles. When a formula has parentheses, like Ca(OH)2, remember the subscript applies to everything inside the parentheses.

Common mistakes to avoid

The most frequent error is adding the atomic mass of an element without multiplying by its subscript — oxygen in H2O counts twice. Second, forgetting that some elements appear as diatomic molecules in reactions (O2, N2, H2) while the formula may list them differently. Third, using the wrong precision: atomic masses from the periodic table are weighted averages, so use the standard values the tool provides. Finally, don't confuse molecular weight (a molecule's mass) with molar mass (one mole's mass) — numerically they match, but the units differ.

Tips for best results

Double-check capitalization — CO is carbon monoxide but Co is cobalt, a 100× difference in mass. Use the periodic table's standard atomic weights, and for calculations that need high precision, round only at the end. When balancing reactions, convert every reactant to moles first, then compare mole ratios — the tool's molar mass is the conversion factor you need. For gases at STP, remember one mole occupies 22.4 L, which lets you move between mass, moles, and volume in one chain.

Authoritative source: timeanddate.com

Frequently asked questions

How do you calculate molecular weight?
Add up the atomic masses of all the atoms in the chemical formula. Multiply each element's atomic mass (from the periodic table) by how many of that atom appear, then sum the results. For water (H₂O): 2 x 1.008 + 15.999 = 18.02 g/mol.
What is the difference between molecular weight and molar mass?
Numerically they are the same for a given substance. Molecular weight (or molecular mass) is technically a relative, unitless ratio to one-twelfth of a carbon-12 atom, while molar mass carries the unit grams per mole (g/mol). In everyday chemistry the terms are used interchangeably.
How do I convert grams to moles?
Divide the mass in grams by the molar mass in g/mol: moles = mass / molar mass. For example, 58.44 g of NaCl (molar mass 58.44 g/mol) is exactly 1 mole. To go the other way, multiply moles by molar mass to get grams.
What is the molar mass of water?
Water (H₂O) has a molar mass of about 18.02 g/mol: two hydrogen atoms at 1.008 each (2.016) plus one oxygen at 15.999, totaling 18.015 g/mol. This means one mole of water — about 6.022 x 10²³ molecules — weighs roughly 18 grams.
Do I include the subscripts and parentheses in the formula?
Yes. Subscripts multiply the atom immediately before them, and a subscript outside parentheses multiplies everything inside. For Ca(OH)₂, you have one calcium, two oxygens, and two hydrogens: 40.08 + 2 x (15.999 + 1.008) = 74.09 g/mol. Counting atoms correctly is the key step.
What does the Molecular Weight Calculator do?
Computes the molar mass of any chemical formula. Enter a formula like H2O or C6H12O6, and the tool sums the atomic masses of every element present using standard atomic weights, returning the molar mass in g/mol, and converts between grams and moles for the. The calculator takes your inputs, applies the standard calculation, and returns a clear result so you can make an informed decision without doing the math by hand.
What formula does the Molecular Weight Calculator use?
The Molecular Weight Calculator applies the standard formula: Molar mass = sum over atoms of (atomic mass x count); moles = mass (g) / molar mass (g/mol). The tool walks through each step of the calculation so you can verify the numbers yourself.
Is the Molecular Weight Calculator free and private?
Yes — the Molecular Weight Calculator. There is no sign-up, no paywall, no trial, and no limit on how many calculations you can run. CalcaTools covers its costs with non-intrusive display advertising, so the calculator itself never asks for payment or restricts any feature.
How accurate is the Molecular Weight Calculator?
The Molecular Weight Calculator applies the standard formula: Molar mass = sum over atoms of (atomic mass x count); moles = mass (g) / molar mass (g/mol). It is tested against published worked examples before launch and uses native double-precision arithmetic, so results are accurate to typical precision for the values you enter — with no intermediate rounding that could distort the answer.

Explore the full everyday toolkit

Every CalcaTools everyday calculator — dates, time, age, measurements, home projects, and lifestyle tools — ready when you need a quick answer.