Elemental composition
| Element | Mass (mono, Da) | Percent (mono) |
|---|---|---|
| C | 72 | 39.9859% |
| H | 12.0939 | 6.7165% |
| O | 95.969488 | 53.2976% |
Show term-by-term mass breakdown (monoisotopic)
| Term | Base element | Count | Mass each (Da) | Subtotal (Da) |
|---|---|---|---|---|
| C | C | 6 | 12 | 72 |
| H | H | 12 | 1.007825032 | 12.0939 |
| O | O | 6 | 15.99491462 | 95.969488 |
Example data table
| Formula | Example | Average (g/mol) | Exact (Da) |
|---|---|---|---|
| C6H12O6 | Glucose | 180.156 | 180.063388 |
| H2O | Water | 18.015 | 18.010565 |
| Fe2(SO4)3 | Iron(III) sulfate | 399.858 | 399.725062 |
| CuSO4·5H2O | Copper(II) sulfate pentahydrate | 249.677 | 248.934151 |
| C8H10N4O2 | Caffeine | 194.194 | 194.080376 |
| [13C]6H12O6 | Glucose labeled (6×13C) | 186.110129 | 186.083517 |
Formula used
- Average molar mass: \( M = \sum n_i \times \bar{m}_i \) (using standard atomic weights)
- Exact mass: \( m_{\text{exact}} = \sum n_i \times m_{i,\text{mono}} \) (using monoisotopic masses)
- Elemental percent: \( \%_i = \frac{m_i}{M}\times 100 \)
- m/z (adduct): \( m/z = \frac{M + \Delta}{|z|} \) where \(z\) is charge and \(\Delta\) is adduct mass shift
- ppm error: \( \text{ppm} = \frac{m/z_{\text{obs}} - m/z_{\text{theory}}}{m/z_{\text{theory}}}\times 10^6 \)
How to use this calculator
- Enter a chemical formula (e.g., C8H10N4O2).
- Use parentheses for grouped atoms (e.g., Fe2(SO4)3).
- Use a centered dot for hydrates/solvates (e.g., CuSO4·5H2O).
- Optional: label isotopes with brackets (e.g., [13C]6H12O6).
- Select an adduct to compute theoretical m/z, and optionally enter observed m/z to get ppm error.
- Download results as CSV or a simple PDF report.
FAQs
1) What is the difference between molecular weight and exact mass?
Molecular weight uses average atomic weights based on natural isotope abundance. Exact (monoisotopic) mass uses the most abundant isotope of each element, matching common high-resolution mass spectrometry workflows.
2) Why is m/z calculated from monoisotopic mass?
For high-resolution spectra, the primary peak often corresponds to the monoisotopic composition. That’s why the calculator uses monoisotopic mass as the base for theoretical m/z.
3) How do hydrates like CuSO4·5H2O work?
The dot indicates an additional formula unit. This calculator splits dot parts, applies any leading multiplier (like 5), then adds all atom counts together before computing masses.
4) Can I include isotopes like 13C or 2H?
Yes. Use bracket notation such as [13C] or [2H]. If that isotope mass is known to the calculator, it replaces the default mass for those labeled atoms.
5) What does ppm error mean?
ppm error reports how far your observed m/z is from the theoretical m/z, scaled by one million. Smaller absolute ppm values generally indicate a closer match.
6) What if my element is not recognized?
The calculator includes a broad set of common elements. If you see “Unknown element,” expand the element list in the code tables or use a supported symbol (capital letter plus optional lowercase).