Question 1

What is molecular weight (molar mass)?

Accepted Answer

The mass of one mole of a substance, expressed in grams per mole (g/mol).

Question 2

Which atomic weights are used?

Accepted Answer

Standard atomic weights from IUPAC; isotopic composition can cause small variations.

Question 3

How do I enter a formula?

Accepted Answer

Use element symbols with counts (e.g., C6H12O6). Parentheses and hydrates like CuSO4*5H2O are supported.

Question 4

Can I calculate mass percent?

Accepted Answer

Yes—mass percent of element = (element mass / total molar mass) * 100%.

Question 5

What precision should I use?

Accepted Answer

Report g/mol with appropriate significant figures for your data; 2-4 decimals are common.

Molecular Weight Calculator