# Molecular Formula Calculator

Find the molecular formula from an empirical formula and experimental molar mass. Calculates the multiplier, molecular formula, and molecular mass.

## What this calculates

Determine the molecular formula of a compound from its empirical formula and experimental molar mass. Enter the number of atoms of each element in the empirical formula and the experimentally determined molar mass to find the whole-number multiplier and true molecular formula.

## Inputs

- **Carbon (C) Atoms** — min 0, max 100 — Number of carbon atoms in the empirical formula.
- **Hydrogen (H) Atoms** — min 0, max 200 — Number of hydrogen atoms in the empirical formula.
- **Oxygen (O) Atoms** — min 0, max 100 — Number of oxygen atoms in the empirical formula.
- **Nitrogen (N) Atoms** — min 0, max 100 — Number of nitrogen atoms in the empirical formula.
- **Sulfur (S) Atoms** — min 0, max 50 — Number of sulfur atoms in the empirical formula (optional).
- **Experimental Molar Mass** (g/mol) — min 0 — Molar mass determined experimentally (e.g., by mass spectrometry).

## Outputs

- **Empirical Formula** — formatted as text — The empirical formula based on the input atom counts.
- **Empirical Formula Mass** (g/mol) — Molar mass of the empirical formula.
- **Multiplier (n)** — Whole number multiplier: n = experimental mass / empirical mass.
- **Molecular Formula** — formatted as text — The molecular formula (empirical formula × n).
- **Molecular Formula Mass** (g/mol) — Calculated molar mass of the molecular formula (should match experimental).

## Details

The empirical formula of a compound gives the simplest whole-number ratio of atoms, while the molecular formula gives the actual number of atoms in one molecule. The molecular formula is always a whole-number multiple of the empirical formula. For example, glucose has an empirical formula of CH₂O and a molecular formula of C₆H₁₂O₆ (n = 6).

To find the molecular formula, first calculate the molar mass of the empirical formula by summing the atomic masses: empirical mass = Σ(atoms × atomic mass). Then divide the experimental molar mass (determined by mass spectrometry, freezing-point depression, or other methods) by the empirical formula mass to get the multiplier n. Multiply each subscript in the empirical formula by n to obtain the molecular formula.

This calculator uses IUPAC 2021 standard atomic weights: C = 12.011, H = 1.008, O = 15.999, N = 14.007, and S = 32.06 g/mol. The multiplier is rounded to the nearest whole number, as molecular formulas must contain integer numbers of atoms.

## Frequently Asked Questions

**Q: What is the difference between empirical and molecular formulas?**

A: The empirical formula gives the simplest whole-number ratio of atoms in a compound (e.g., CH₂O), while the molecular formula gives the actual number of atoms per molecule (e.g., C₆H₁₂O₆ for glucose). The molecular formula is always a whole-number multiple of the empirical formula. Some compounds have the same empirical and molecular formula (e.g., H₂O, CO₂).

**Q: How do I find the empirical formula from percent composition?**

A: Convert each element's mass percentage to grams (assume 100 g sample), divide each by its atomic mass to get moles, then divide all mole values by the smallest to get the simplest ratio. If the ratios are not close to whole numbers, multiply all by the smallest integer that gives whole numbers.

**Q: Why might the multiplier not be exactly a whole number?**

A: Experimental molar mass measurements always have some degree of uncertainty. The raw ratio (experimental mass / empirical mass) may be something like 5.93 or 6.08 instead of exactly 6. The calculator rounds to the nearest whole number. If the ratio is far from any integer (e.g., 3.5), it may indicate an error in the empirical formula or experimental molar mass.

**Q: Can this calculator handle elements besides C, H, O, N, and S?**

A: This calculator supports the five most common organic elements: carbon, hydrogen, oxygen, nitrogen, and sulfur. For compounds containing other elements (halogens, phosphorus, metals), you would need to calculate the empirical formula mass manually and use the same principle: n = experimental mass / empirical mass.

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Source: https://vastcalc.com/calculators/chemistry/molecular-formula
Category: Chemistry
Last updated: 2026-04-21