Molecular weights of common lab chemicals

Updated November 8, 2026

Formula weights for 57 reagents used in molecular biology, cell culture and protein work. Click Calculate on any row to open the molarity calculator with that molecular weight filled in.

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Check the hydrate on your bottle

Many salts are sold in several hydrated forms, and the water of crystallisation counts toward the weight. Magnesium chloride hexahydrate (MgCl₂·6H₂O, 203.30 g/mol) weighs more than twice as much per mole as anhydrous MgCl₂ (95.21 g/mol). Using the wrong one gives a solution at less than half or more than double the intended concentration. Always use the formula weight printed on the label of the bottle you are weighing from.

Liquids

For liquid reagents such as glycerol, DMSO and β-mercaptoethanol it is easier to measure volume. Convert using density: grams = mL × density. For example, 1 mL of glycerol weighs about 1.26 g, which is 13.7 mmol.

Antibiotics and salts with variable potency

Antibiotic working concentrations are usually given as µg/mL rather than molarity, and some antibiotics (such as G418 or kanamycin) are sold with lot-specific potency. Follow the supplier's certificate of analysis when exact concentration matters.