Type or draw
Enter a formula like C8H10N4O2, Ca(OH)2 or CuSO4·5H2O in the calculator, or draw the molecule or paste its SMILES.
WAVESPEED AI MOLECULAR WEIGHT CALCULATOR Structures stay on your device
100% FREE
Molecular Weight CalculatorFrom a formula or a drawing.
Type a formula, with brackets and hydrates, or draw the structure to get its average molecular weight, exact (monoisotopic) mass and elemental composition.
Drawn structures also show logP, TPSA, H-bond counts and Lipinski's rule of five.
Average and exact massElemental compositionFormula or structure
No sign-up No upload Nothing to install
Loading the structure editor…
Drawings and files are processed in your browser and never uploaded.The chemistry engine downloads once (about 3 MB) and is then cached.
THREE SIMPLE STEPS
How to use the Molecular Weight Calculator
Read the masses
See the molecular weight in g/mol, the exact mass in Da and the mass percentage of each element.
Go further
For drawn structures, copy the SMILES or InChIKey, check Lipinski's rule of five and export images or files.
WaveSpeed AI
Make visuals for your chemistry.
Turn molecules into illustrations, cover art and explainer clips for slides, papers and lessons with WaveSpeed AI.
Image Generator
Create journal-cover style art and lab illustrations from a description.
Video Generator
Animate an illustration into a short explainer clip.
3D Generator
Make a 3D model of lab equipment or a stylised molecule.
- 1,000+ AI models
- Image, video and 3D
- Pay as you go
$1 in free credits for eligible new accounts. No card needed. Generators have separate account and credit requirements. The structure drawer is free.
/filters:quality(82)/media/images/1791123751656780930_IfFPY7R0.webp){kind=small}
/filters:quality(82)/media/images/1791123737177812425_RjKT3cku.webp){kind=small}
/filters:quality(82)/media/images/1791123748309870128_xlkNgK8N.webp){kind=small}
/filters:quality(82)/media/images/1791123738630744263_oR09R0aj.webp){kind=small}
/filters:quality(82)/media/images/1791177033162457776_uQ09OY7g.webp){kind=small}
/filters:quality(82)/media/images/1791123734319125607_JdnwGPY7.webp){kind=small}
/filters:quality(82)/media/images/1791123746355630206_udnxGPY7.webp){kind=small}
/filters:quality(82)/media/images/1791123744771362580_yC0sPezZ.webp){kind=small}
/filters:quality(82)/media/images/1791123738606970169_5KIR1ais.webp){kind=small}
/filters:quality(82)/media/images/1791123748197655725_EUmuFNW6.webp){kind=small}
Molecular Weight Calculator FAQ
Is the molecular weight calculator free?
Yes, with no account and no limits.
Which atomic weights are used?
Standard atomic weights for the average molecular weight and the most abundant isotope for the exact mass, the same values used by the RDKit cheminformatics toolkit.
Can I enter hydrates and charged ions?
Yes. Use a dot or · for hydrates (CuSO4·5H2O), brackets for groups (K3[Fe(CN)6]) and a trailing charge such as SO4-2 or SO4^2-. D and T stand for deuterium and tritium.
What is the difference between molecular weight and exact mass?
Molecular weight averages over natural isotope abundances and is used for weighing out compounds; exact mass uses the most abundant isotope of each element and is what a high-resolution mass spectrometer measures.
More free tools like this
All Free Tools
Molecular Weight Calculator
Average and exact mass · Elemental composition · Formula or structure