How to Calculate Molar Mass

Editorial Team · 2 min read

Molar mass is the mass of one mole of a substance. It is usually written in grams per mole. This guide explains how to calculate molar mass in plain language, with formula steps, examples, a quick reference table, and common mistakes to avoid.

Last updated: June 2026.

Quick answer

Formula: Molar mass = sum of each element atomic mass x number of atoms in the formula.

Example: Water, H2O, has molar mass about 18.02 g/mol: 2 x 1.008 + 16.00.

How to calculate it step by step

1. Step 1: Write the chemical formula.
2. Step 2: Find each element atomic mass.
3. Step 3: Multiply by the subscript.
4. Step 4: Apply parentheses multipliers.
5. Step 5: Add all element contributions.

If you need to handle decimal atomic masses, the Scientific Calculator can keep the arithmetic tidy.

Example table

Common mistakes

• Mixing units, such as inches with feet, percentages with decimals, or sample data with population data.
• Skipping the formula and copying a result without checking whether the inputs match the question.
• Rounding too early, which can change the final answer when several steps are involved.
• Using an estimate for a decision that needs an official source, professional review, lab instruction, medical advice, or accounting records.

When to use a calculator

A calculator is most useful when the formula is clear but the arithmetic could distract you. Use it to check multiplication, division, powers, square roots, percentages, fractions, and repeated scenarios. For learning, write the formula first, then use the calculator to confirm the final number.

Search variations this answers

People search this topic in different ways, including molar mass formula, molecular weight calculation, grams per mole. Instead of creating separate thin pages for each variation, this article groups the shared intent into one complete explanation.

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