Last updated: October 2026
How to find the empirical formula
Short answer: turn each element into moles, divide by the smallest mole value, then scale the ratios to whole numbers. The calculator above shows every step in the mole table.
- Convert to moles. Divide each element's value by its atomic weight: moles = value ÷ atomic weight.
- Find the smallest. Look at the mole values and note the smallest one.
- Divide everything by the smallest. This gives the mole ratio, with at least one value exactly 1.
- Scale to whole numbers. Multiply all ratios by the smallest integer (1–12) that makes them integers — e.g. 1.5 → ×2, 1.33 → ×3. Those integers are the subscripts.
The empirical formula is the simplest whole-number ratio of atoms in a compound — glucose is C₆H₁₂O₆ but its empirical formula is CH₂O. Read the background on Wikipedia's empirical formula article.
Empirical formula from percent composition
Short answer: read each percentage as grams in a 100 g sample — 40% carbon is 40 g of carbon — then run the standard moles method. Use the calculator's Percent mode.
This is the most common homework setup, and it's why this query gets searched 200 times a month. The trick is just the 100 g assumption: percentages convert directly to grams, and from there the method is identical to the mass version. The calculator's Percent mode applies exactly this logic — try the "Glucose analysis" preset above to see it in action.
From mass to moles: the conversion that makes it work
Short answer: moles = mass ÷ atomic weight. A gram of hydrogen is ~1 mole; a gram of oxygen is ~0.0625 moles — mass alone tells you nothing about atom counts until you convert.
moles = mass (g) ÷ atomic weight (g/mol)
ratio = moles ÷ smallest mole value
subscript = round(ratio × k), smallest k in 1..12
Mass is what you can weigh; moles are what chemistry counts in. The calculator carries the standard atomic weights (IUPAC 2021) for all 118 elements, so it converts any element automatically.
Mole ratios: where the whole numbers come from
Short answer: dividing every mole value by the smallest one turns raw moles into a clean ratio like 1 : 2 : 1 — those numbers become the formula subscripts.
Atoms combine in whole-number ratios, so the ratio step is where the chemistry happens. If dividing gives 1.5, the true ratio is probably 3:2 — multiply everything by 2. The calculator tries multipliers 1 through 12 and picks the cleanest fit; if nothing fits well it warns you instead of silently rounding.
Empirical vs molecular formula
Short answer: the molecular formula is the empirical formula multiplied by a whole number n, found from the molar mass: n = round(molar mass ÷ empirical formula mass).
Empirical CH₂O could be formaldehyde (30 g/mol), glucose (180.16 g/mol) or anything in between — the molar mass decides. Enter it in the optional field and the calculator multiplies the subscripts for you. Try the "Glucose + 180.16 g/mol" preset: CH₂O × 6 → C₆H₁₂O₆.
Every element on the periodic table works
Short answer: type any element symbol — H to Og, all 118 — and the calculator knows its atomic weight. Symbols are case-insensitive (na, NA and Na all work).
Most online tools only cover a dozen common elements. This one embeds the full standard atomic-weight table, including the lanthanides, actinides and synthetic elements (using the most stable isotope's mass where no standard weight exists). No external lookups, no network calls — it's all in the page.
More chemistry calculators coming soon
Short answer: this page is the first of our chemistry cluster. A molecular formula calculator, a molar mass calculator and a stoichiometry calculator are next.
Bookmark this page — the chemistry series is growing, and these tools are designed to link to each other, so related calculations stay one click away. For now, our scientific calculator and significant figures calculator cover the math around chemistry homework.
Frequently asked questions
What is the empirical formula calculator?
It's a free tool that finds a compound's empirical formula — the simplest whole-number ratio of atoms — from percent composition or element masses. Enter each element and its value, and it converts to moles, divides by the smallest, and scales to whole numbers, showing every step.
How do I calculate the empirical formula?
Convert each element's mass (or percent) to moles by dividing by its atomic weight, divide every mole value by the smallest, then multiply by a small whole number (1–12) until the ratios become integers. The calculator above does all three steps and shows its working.
How do I find the empirical formula from percent composition?
Treat the percentages as grams in a 100 g sample — 40% carbon is 40 g of carbon. Then follow the usual steps: grams ÷ atomic weight = moles, divide by the smallest mole value, scale to whole numbers. Use the Percent mode on the calculator and it handles the conversion.
How do I find the empirical formula given percentages?
Same thing as percent composition: read each percentage as grams per 100 g, convert to moles with each element's atomic weight, divide all mole values by the smallest, and round to whole numbers. The calculator's Percent mode is built exactly for this.
What is a compound formula calculator in chemistry?
It's the same class of tool: a chemistry calculator that works out a compound's formula from composition data. This page is one — it computes the empirical formula from percent or mass data, and the molecular formula when you also give it the molar mass.
How do I go from empirical to molecular formula?
Divide the molar mass by the empirical formula mass and round to a whole number n, then multiply every subscript in the empirical formula by n. For example, CH2O has an empirical mass of about 30 g/mol; with a molar mass of 180.16 g/mol, n = 6, giving C6H12O6. Enter the molar mass on the calculator and it does this automatically.
Is this the same as an empirical rule formula calculator?
No — that's a different topic. This page is about the empirical formula in chemistry (simplest atom ratio in a compound). The 'empirical rule' is a statistics concept (the 68-95-99.7 rule for normal distributions). Similar names, unrelated tools.
Is my data private?
Completely. Every calculation runs locally in your browser with JavaScript — your numbers are never sent to a server, stored, or tracked.
