Calculate Molecular Weight
Learn how to calculate molecular weight step by step. Enter any chemical formula to see the complete calculation process: element identification, atomic weight lookup, multiplication, and summation. This guide walks you through the exact method used by chemistry students and professionals to compute molecular weight from any formula.
Ingrese una fórmula química arriba para calcular el peso molecular
The Step-by-Step Calculation Process
See how molecular weight is calculated character by character as you type.
To calculate molecular weight, you need three pieces of information for each element: the element symbol, the number of atoms (from subscripts and group multipliers), and the standard atomic weight from the IUPAC periodic table.
The formula MW = Σ(Aᵢ × nᵢ) sums the products of atomic weight (Aᵢ) and atom count (nᵢ) for every element i. For H₂SO₄: H: 1.008×2 = 2.016, S: 32.065×1 = 32.065, O: 15.999×4 = 63.996. Total: 98.078 g/mol.
This calculator automates the entire process — handling parentheses, brackets, nested groups, and all 118 elements — so you can focus on understanding the method rather than manual arithmetic.
Standard Atomic Weights for Calculation
Every molecular weight calculation requires accurate atomic weights from the periodic table.
The second step in calculating molecular weight is looking up the standard atomic weight for each element. These values come from the IUPAC 2021 periodic table and represent weighted averages of natural isotope abundances.
For common elements used in organic chemistry: Carbon (12.011), Hydrogen (1.008), Nitrogen (14.007), Oxygen (15.999), Sulfur (32.065), and Phosphorus (30.974). Memorizing these six values lets you quickly estimate molecular weights of most organic compounds.
For inorganic and transition metal compounds, the atomic weights vary widely — from Beryllium (9.012) to Uranium (238.029). Explore the cards below to see atomic weights used in molecular weight calculations.
How to Calculate Molecular Weight Manually
The 3-step method to calculate molecular weight from any chemical formula.
Step 1: Write the Formula
Write out the chemical formula of your compound. Identify each element symbol and its subscript number. For Ca(OH)₂: you have Ca appearing once, O appearing twice (inside parentheses × 2), and H appearing twice (inside parentheses × 2). This step-by-step approach ensures no atoms are missed.
Molecular Weight Calculation Examples
Click any compound to see the step-by-step calculation in the calculator.
How to Calculate Molecular Weight — FAQ
Common questions about the molecular weight calculation method.