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Formula Mass Calculator

Find the empirical formula from percent composition.

About Formula Mass Calculator

The empirical formula for Formula Mass converts percent composition to moles by dividing each percentage by the element's molar mass, then reduces to a simple ratio. The empirical formula is the smallest whole-number ratio, which is what spectroscopy and combustion data provide.

Formula

Formula Mass

Mole ratio = (percent / molar mass) for each element

empirical formula
The simplest whole-number ratio of elements

Worked example

With the default values below, Formula Mass Calculator returns Mole Ratio of 0.252. Change any input above and every figure here is recalculated in your browser.

Inputs used

Element 1 percentaccepts 0–100 %
74.87 %
Element 2 percentaccepts 0–100 %
25.13 %
Element 1 molar massminimum 0 g/mol
12.01 g/mol

Results

Mole Ratio
0.252
Element 2 Moles
1.571 mol
Simplified Ratio
0.252

Step by step

  1. 1Values used
  2. 2Formula Mass
  3. 3Mole Ratio= 0.252
  4. 4Element 2 Moles= 1.571 mol
  5. 5Simplified Ratio= 0.252

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Formula Mass calculated?

Mole ratio = (percent / molar mass) for each element The empirical formula for Formula Mass converts percent composition to moles by dividing each percentage by the element's molar mass, then reduces to a simple ratio.

Why does Formula Mass matter?

The empirical formula is the smallest whole-number ratio, which is what spectroscopy and combustion data provide.

What values do I need to enter?

This calculator takes 3 inputs: Element 1 percent, Element 2 percent, Element 1 molar mass. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

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