DMSO Molar Mass: 78.13 g/mol and Conversions

DMSO (dimethyl sulfoxide, C₂H₆OS) has a molar mass of about 78.13 g/mol. NIST lists 78.133, PubChem lists 78.14 and the ILO-WHO International Chemical Safety Card lists 78.1; all describe the same compound (CAS 67-68-5), and the differences are rounding.

Short answer

Use 78.13 g/mol for routine bench work. One mole of DMSO weighs about 78.13 g, so 7.813 g is 0.1 mol. Because DMSO is a liquid at room temperature, measuring it by volume needs its density as well (below).

Definition and scope

Molar mass is the mass of one mole of a substance, expressed in grams per mole. For a small molecule such as DMSO it is the same number as the molecular weight, which NIST reports without units for the same formula. The formula is C₂H₆OS and the IUPAC name given by PubChem is methylsulfinylmethane. The NIST Chemistry WebBook lists the InChIKey IAZDPXIOMUYVGZ-UHFFFAOYSA-N, and the ICSC spells the name dimethyl sulphoxide. The CAS Registry Number is 67-68-5.

How the number is used in practice

The molar mass converts between the mass of a substance and the amount in moles: moles = mass in grams / 78.13 g/mol. For a liquid, a second conversion links volume to mass through density. PubChem lists a density of 1.100 at 20/4 C and 1.101 at 25 C, and the ICSC gives a relative density of 1.1 (water = 1).

Worked conversions (arithmetic from the sourced values)

Mass to moles: 7.813 g / 78.13 g/mol = 0.1000 mol.
Volume to moles: 10.0 mL x 1.100 g/mL = 11.0 g; 11.0 g / 78.13 g/mol = 0.141 mol.
Moles to volume: 0.100 mol x 78.13 g/mol = 7.813 g; 7.813 g / 1.100 g/mL = 7.10 mL.
Concentration of the neat liquid: 1.100 g/mL x 1000 mL/L / 78.13 g/mol = about 14.1 mol/L.

These use the 20 C density; at another temperature the density, and therefore the volume figures, shift slightly. The general method for turning moles into a target molarity is in Molarity and Solution Calculations for the Lab.

Values reported by each source

Source	Molar mass / molecular weight	Other values listed
NIST Chemistry WebBook	78.133	Formula C2H6OS; CAS 67-68-5
PubChem (CID 679)	78.14 (exact mass 78.01393598)	Density 1.100 at 20/4 C; IUPAC name methylsulfinylmethane
ILO-WHO ICSC 0459	78.1	Melting point 18.5 C; boiling point 189 C; flash point 87 C (closed cup)

Exact mass (78.0139) is a different quantity from molar mass: it is the mass of the molecule built from the most abundant isotopes, and is the figure relevant to mass spectrometry. Molar mass is the abundance-weighted average used for weighing and solution work.

Where it matters for labs and supply decisions

It freezes near room temperature. The ICSC gives a melting point of 18.5 C, so DMSO stored in a cool room can be solid. Check that it is fully liquid and mixed before measuring a volume.
It is hygroscopic. The ICSC describes DMSO as a colourless hygroscopic liquid, so an open container takes up water, and a stock solution made by mass from a long-open bottle contains less DMSO per gram than the table assumes.
It passes through skin. The ICSC states it can be absorbed through the skin, by inhalation and by ingestion, and that it may accelerate skin absorption of other materials. It adds that special attention is needed when toxic materials are dissolved in DMSO because of enhanced skin absorption. Handling therefore calls for protective gloves and eye protection as set out by your institution’s safety data sheet and chemical hygiene plan.

For a related low-temperature use of DMSO, see CASRAI’s cryopreservation of cells guide. For solvent choice more broadly, see the green chemistry lab guide.

Common misunderstandings

Molar mass is not density. 78.13 g/mol converts moles to grams; 1.100 g/mL converts grams to millilitres. Using one in place of the other gives a volume about 71 times too large or too small.
Different decimal places are not different compounds. 78.133, 78.14 and 78.1 are one substance reported at different precision. Choose the number of significant figures your measurement can support and keep it consistent across a protocol.
Molar mass is not exact mass. Use 78.01394 only when interpreting a mass spectrum.

FAQ

What is the molar mass of DMSO?

About 78.13 g/mol (NIST: 78.133; PubChem: 78.14).

What is the chemical formula of DMSO?

C₂H₆OS, CAS 67-68-5.

Is the molar mass of DMSO the same as its molecular weight?

Numerically yes, for a small molecule such as DMSO; molar mass carries units of g/mol and molecular weight is dimensionless.

How many millilitres of DMSO are in one mole?

About 71.0 mL at 20 C (78.13 g / 1.100 g/mL).

Sources

All three records were checked on 2026-10-29.

NIST Chemistry WebBook, dimethyl sulfoxide: https://webbook.nist.gov/cgi/cbook.cgi?ID=C67685&Units=SI
PubChem compound record CID 679, dimethyl sulfoxide: https://pubchem.ncbi.nlm.nih.gov/compound/679
ILO-WHO International Chemical Safety Card 0459, dimethyl sulphoxide: https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0459

Ask about DMSO Molar Mass: 78.13 g/mol, Formula and Conversions

Ask your first 2 questions free below. Subscribers get 150 a day for $29 a month.

An AI assistant specialized in research administration. It cites the sources behind every answer, labels web answers and says when it can't answer.

Answers draw on CASRAI's guides and dictionary plus the federal and funder documents we index: Federal Register, Grants.gov, Regulations.gov and UKRI.

Everything CASRAI publishes — this page, the dictionary, the guides and the news — stays free to read, with no account and no card.