Molecular Weight Calculator
Calculate the molar mass of any chemical compound from its formula
Frequently Asked Questions
Calculating the molar mass of a chemical compound from its formula means summing the atomic weights of every atom in the formula, weighted by how many times each element appears — a calculation that requires correctly parsing the formula's subscripts and any grouped/parenthesized portions, since a misread formula produces a systematically wrong molar mass.
Why molar mass is a sum, not a lookup
Every element has a standard atomic weight (average, accounting for natural isotope abundance) — molar mass of a compound is calculated by multiplying each element's atomic weight by its subscript count in the formula, then summing across every element present. A formula like a compound containing parenthesized groups (common in more complex compounds) requires the subscript inside the parentheses to be multiplied by the group's own outer multiplier as well — getting this nested multiplication wrong is one of the most common sources of an incorrect molar mass calculation, since it's easy to apply a group's multiplier to only part of the formula rather than the entire parenthesized group.
A worked example
A compound formula with a multi-atom group in parentheses, followed by a subscript outside the parentheses, requires multiplying every atom count inside the parentheses by that outside subscript before summing atomic weights — treating the parenthesized group as if its internal atom counts were final (without applying the outer multiplier) undercounts several atoms' contribution to the total molar mass.
How this connects to your other science calculations
Molar mass is the direct conversion factor between a compound's mass (grams) and its amount in moles — this conversion is typically the necessary first step before a Molarity Calculator calculation, since molarity is defined in terms of moles of solute, not grams, and grams need converting to moles via molar mass first.
Common mistakes
Misapplying (or forgetting entirely) a parenthesized group's outer multiplier to every atom inside that group is the most common formula-parsing error — always double-check that every element's effective count accounts for both its own subscript and any group multiplier it's nested inside, rather than reading subscripts in isolation from the formula's overall structure.