---
title: "Molar mass calculator — free, runs in your browser"
description: "Molecular weight from a chemical formula, with the per-element breakdown. Free, no sign-up, and nothing you enter leaves your browser."
url: https://atoneplace.net/tools/molar-mass-calculator/
site: "At One Place"
---

# Molar mass calculator

Molecular weight from a chemical formula, with the per-element breakdown.

## How it works

Parses a chemical formula and returns its molar mass, showing each element’s contribution. Handles nested brackets and hydrates, so Ca(OH)₂ and CuSO₄·5H₂O both work.

Molar mass in grams per mole is numerically equal to the molecular mass in atomic mass units, which is the whole point of the mole — it is defined so that the bridge between the atomic scale and the laboratory bench is a factor of one rather than Avogadro’s number.

Case matters in formulas and is the commonest input error. Co is cobalt; CO is carbon monoxide. There is no way for a parser to guess which you meant, so it takes the case literally.

Values use the IUPAC standard atomic weights, which are averages weighted by natural isotopic abundance. For elements whose abundance varies measurably by source — notably carbon, hydrogen and lithium — IUPAC publishes an interval rather than a single value, and the conventional single figure is used here.

> This tool runs entirely in your browser. Nothing you enter is sent to a server, logged or stored, and the page keeps working with the network disconnected.

## Common questions

### What is molar mass?

The mass of one mole of a substance, in grams per mole. It is numerically equal to the molecular mass in atomic mass units.

### Why does CO give a different answer from Co?

Because they are different things — carbon monoxide versus cobalt. Chemical formulas are case-sensitive and the parser takes them literally.

### How do I enter a hydrate?

Use a dot or an asterisk, as in CuSO4.5H2O. The parser multiplies the water portion correctly.

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## Sources

- Calculated on this page — At One Place (/about/)