Percent Composition Calculator
Mass percent of each element, or of a solute in a solution.
Enter your values
Enter the mass of the element or solute in g or g/mol.
Enter the number of atoms of that element you are working with.
Enter the total mass of the compound in g or g/mol.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Percent composition
- 27.2921 %
- Mass contributed
- 12.011 g
- Remaining mass
- 31.998 g (72.7079%)
Working
- 1Mass of element = 12.011 × 1 = 12.011
- 2Percent = 12.011 ÷ 44.009 × 100 = 27.2921%
Quick answer
Percent composition is the mass of a component divided by the total mass of the compound, times 100: % = (mass of part / total mass) × 100.
% composition = (mass of element / molar mass of compound) × 100
At a glance
| What it does | Mass percent of each element, or of a solute in a solution. |
|---|---|
| Category | Science |
| Inputs needed | Mass of the element or solute, Number of atoms of that element, Total mass of the compound |
| Main output | Percent composition |
| Formula | % composition = (mass of element / molar mass of compound) × 100 |
| Cost | Free — no sign-up, no download |
How to use the Percent Composition Calculator
- 1Enter the atomic or molar mass of the element and how many atoms appear in the formula.
- 2Enter the molar mass of the whole compound.
- 3Read the mass percent.
Inputs explained
- Mass of the element or solute(g or g/mol)
- Enter the mass of the element or solute in g or g/mol.
- Number of atoms of that element
- Enter the number of atoms of that element you are working with.
- Total mass of the compound(g or g/mol)
- Enter the total mass of the compound in g or g/mol.
Worked example
Using the values the calculator loads with:
Inputs
- Mass of the element or solute12.011 g or g/mol
- Number of atoms of that element1
- Total mass of the compound44.009 g or g/mol
Results
- Percent composition27.2921 %
- Mass contributed12.011 g
- Remaining mass31.998 g (72.7079%)
- Mass of element = 12.011 × 1 = 12.011
- Percent = 12.011 ÷ 44.009 × 100 = 27.2921%
Frequently asked questions
How do you find percent composition?
Divide the total mass of the element in one mole of the compound by the compound's molar mass, then multiply by 100.
What is the percent carbon in CO₂?
Carbon contributes 12.011 g/mol out of 44.009 g/mol, so CO₂ is 27.29% carbon by mass and 72.71% oxygen.
What do I need to enter into the Percent Composition Calculator?
Just 3 values: mass of the element or solute, number of atoms of that element, total mass of the compound. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Percent Composition Calculator work out the answer?
Percent composition is the mass of a component divided by the total mass of the compound, times 100: % = (mass of part / total mass) × 100. It applies the formula % composition = (mass of element / molar mass of compound) × 100 and shows the working so you can check each step by hand.
Is the Percent Composition Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.