Mass to Moles Converter
Convert between mass and moles.
About Mass to Moles Converter
Moles = mass/molar mass. This conversion connects macroscopic measurements to the molecular scale.
$$n = \frac{m}{M_w}$$
How to use this calculator
- Enter the mass of the substance in grams, using the value you want to convert.
- Enter the molar mass, or molecular weight, in grams per mole, 1g/mol.
- Click calculate to get the amount in moles.
- If needed, use the result to compare substances or plug it into a reaction calculation.
The formula explained
The formula n = rac{m}{M_w} computes the number of moles n by dividing the mass m by the molar mass M_w. It works because molar mass tells you how many grams make up one mole of a substance.
- n = number of moles
- m = mass of the substance in grams
- \(M_w\) = molar mass of the substance in grams per mole
Step by step method
- Start with the given mass in grams and the molar mass in grams per mole.
- Substitute the values into n = rac{m}{M_w}.
- Divide to find the number of moles.
Worked example
Problem. Find the number of moles in 24.0 g of water if the molar mass of water is 18.0 g/mol.
- Substitute the values into the formula: n = rac{24.0}{18.0}.
- Compute the division: n = 1.333....
- Round to a reasonable value: n 1.33 mol.
Answer. 1.33 mol
Tips and common mistakes
- Make sure the mass is in grams and the molar mass is in g/mol before calculating.
- A larger molar mass gives fewer moles for the same mass, so always check units carefully.
Frequently asked questions
How do I convert mass to moles with this calculator?+
Enter the mass of your sample and its molar mass, then the tool uses n = m / Mw to calculate moles. The mass should be in grams and the molar mass should be in grams per mole.
What does the formula n = m / Mw mean?+
In the formula, n is the amount of substance in moles, m is the mass of the sample, and Mw is the molar mass. It shows that moles equal mass divided by grams per mole, so heavier samples give more moles when the molar mass stays the same.
What should I do if I only know the chemical formula, not the molar mass?+
First calculate the molar mass from the formula using atomic masses from the periodic table, then enter that value into the converter. For example, water has a molar mass of about 18.015 g/mol.
Can I use this tool for very small or very large masses?+
Yes, the same equation works for any size value as long as the units are consistent. If the result is a decimal, that is normal, for example a small mass can correspond to less than 1 mole.
How is mass to moles conversion different from moles to mass?+
Mass to moles divides by molar mass, while moles to mass multiplies by molar mass. They are inverse calculations, so using the wrong direction will give the wrong unit and result.
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