CHEMISTRY, MADE CLEAR
Grams to moles.
From the mass you have to the amount you need.
Enter a formula. See the result. Understand the working.
Your conversion
FREE · NO SIGN-UP10 g of H₂O equals
0.555093 mol
555.093 mmol · 555093 µmol
The working
Amount = mass ÷ molar mass
10 g ÷ 18.015 g/mol
= 0.555093 mol
Rounding changes the display, not the calculation. Atomic-weight uncertainty and your measurement precision still apply.
LOOK INSIDE THE FORMULA
Every element, accounted for.
| Element | Atoms | Atomic weight | Contribution (g/mol) | Mass share |
|---|
Using the central values from CIAAW's 2024 abridged standard atomic weights. No isotope mass numbers are substituted for missing standard weights.
MORE THAN ONE VALUE?Convert a batch
Use the substance, direction, and units selected above. Enter up to 250 values separated by new lines, commas, or semicolons. Do not use thousands separators.
| Mass (g) | Amount (mol) |
|---|
THE METHOD
A mole connects
the measurable
to the molecular.
Grams measure mass. Moles measure the amount of a substance. The bridge between them is that substance's molar mass.
For a sample with mass m in grams and molar mass M in grams per mole, the amount n is n = m / M. To go the other way, use m = n × M. Because different substances have different molar masses, there is no single grams-to-moles conversion factor.
Start with the right chemical formula
The calculator adds the atomic weights for every atom in your formula. For water, H2O means two hydrogen atoms and one oxygen atom: (2 × 1.008) + 15.999 = 18.015 g/mol. A 10 g sample therefore contains approximately 0.555093 mol of water.
Parentheses multiply a group: Ca(OH)2 contains one calcium, two oxygen, and two hydrogen atoms. A hydrate dot adds another component: CuSO4·5H2O includes five water molecules per copper sulfate formula unit. Include that water when weighing a hydrate.
Units and precision, made explicit
One kilogram is 1,000 grams; one milligram is 0.001 grams. One mole is 1,000 millimoles or 1,000,000 micromoles. The app handles these factors before displaying your result. Choose the significant figures appropriate to your starting measurement. Extra displayed digits do not improve the accuracy of the sample mass or the atomic-weight data.
A few useful reference points
Mass of 1 moleSelect a substance to load it into the calculator. These values describe the named formula, not the purity of a real sample.
GOOD QUESTIONS
A little more clarity.
How do I convert grams to moles?
Divide the mass in grams by the substance's molar mass in g/mol. For example, 58.44 g of pure NaCl divided by 58.44 g/mol is 1 mol. Enter your formula to calculate its molar mass automatically, or provide a known molar mass in custom mode.
Why does the formula need capital letters?
Element symbols are case-sensitive. Co is cobalt; CO is carbon monoxide, with one carbon and one oxygen. The calculator preserves that distinction instead of guessing. Use the standard capital first letter and lowercase second letter, where applicable.
Can I enter hydrates, brackets, or subscripts?
Yes. Use formulas such as CuSO4·5H2O, Ca(OH)2, and K4[Fe(CN)6]. Unicode subscripts such as H₂O are accepted. A period is treated as a hydrate separator, so CuSO4.5H2O works too. Fractional atom counts, charges, isotope labels, state symbols such as (aq), and reaction equations are unsupported. Enter a formula without reaction coefficients. Use a custom molar mass when your material requires isotope-specific values.
What if my sample is a mixture or an impure chemical?
A mixture does not generally have one molecular formula. Calculate each component separately using its own mass and molar mass. If you know a compound's mass fraction in an impure sample, first multiply the total sample mass by that fraction. This calculator does not infer composition or purity.
Is molar mass the same as molecular weight?
Molar mass has units such as g/mol. Relative molecular mass is dimensionless; molecular mass may be expressed in daltons. For ordinary chemistry calculations their familiar numerical values are effectively the same, but the quantities and units are different. This tool uses molar mass in g/mol.
Where do the atomic weights come from?
The formula tool uses the central values from the Commission on Isotopic Abundances and Atomic Weights (CIAAW) 2024 abridged table. Natural isotope distributions vary, and the table includes uncertainties that this calculator does not propagate. Elements without a standard atomic weight are rejected; enter an appropriate molar mass in custom mode for those materials.
Are my calculations stored?
The calculation runs in your browser. This app does not send the entered formula, sample mass, or batch values to a calculation service and does not save them in local storage. Copying, printing, and downloading are actions you control.
OUR APPROACH
One job.
Every detail considered.
Grams to Moles exists to make this small, essential part of chemistry easier. A useful calculator should accept the formulas you actually work with, keep units visible, and show how it reached the answer. It should work just as comfortably on a phone as it does beside a lab notebook.
That's what we're building: a focused, full-featured chemistry tool, free to use. No account, no calculation limits hidden behind a paywall, and no black box between your question and its answer.
Method & sources
- CIAAW — Abridged Standard Atomic Weights 2024: the 84 supported elements and their abridged central values.
- CIAAW — Standard Atomic Weights: isotope variability and source uncertainties.
- BIPM — SI base units: the mole as the SI unit of amount of substance.
Data checked September 2026. Calculations are educational tools; verify material identity, purity, and required precision for your application.