Micromolar to Molar Converter
Common Conversions
| µM | M |
|---|---|
| 0.1 | 1e-7 |
| 1 | 0.000001 |
| 10 | 0.00001 |
| 100 | 0.0001 |
| 1000 | 0.001 |
| 10000 | 0.01 |
| 50000 | 0.05 |
| 100000 | 0.1 |
| 500000 | 0.5 |
| 1000000 | 1 |
| 5000000 | 5 |
Why this conversion matters in chemistry
Pharmacology and biochemistry assays live in micromolar — drug screening hits at 5 µM, enzyme substrates dosed at 100 µM. Stocks are stored in molar — typically a 10 mM DMSO master from a solid sample. Going from µM to M is dividing by a million, the bookkeeping that lets the working concentration in a well meet the dilution math from the stock. A 5 µM IC50 in mol/L is 5 × 10⁻⁶ M; getting the prefix right is what separates a confident structure-activity comparison from one off by three orders of magnitude.
Formula
Where the factor comes from
Since 2019 the mole has been defined by fixing the Avogadro constant at exactly 6.02214076 × 10²³ entities per mole. It is no longer tied to twelve grams of carbon-12; that former anchor became a measured quantity, still 12 g/mol to within roughly a part in a billion but no longer exact. Worth knowing and, for this pair, beside the point — the mole appears identically on both sides and cancels, as does the liter of solution underneath. One prefix is left standing: micro, defined as 10⁻⁶. So 1 µM is 10⁻⁶ mol/L, and going from µM to M is a division by exactly one million. No density, no molar mass and no temperature correction enters, so the factor contributes nothing to the uncertainty of the result.
Precision and significant figures
A factor of 10⁶ moves the decimal six places and does nothing else: 25 µM is 2.5 × 10⁻⁵ M, two significant figures either way. The practical hazard is decimal form rather than rounding. Written out, 0.000025 M invites a miscounted zero in a way that 25 µM never does, which argues for scientific notation on any molar value below about 10⁻³. Actual precision is set far upstream. Micromolar concentrations are usually reached by serial dilution from a concentrated stock, and each transfer adds its own pipetting error, so two or three significant figures is what such a chain honestly supports. An exact factor launders none of that.
Worked Examples
The conversion anchor — one molar is exactly one million micromolar.
A typical screening-assay starting concentration before a dose-response titration begins.
One micromolar — a respectable potency for a kinase or GPCR ligand at the early-discovery stage.
Ten millimolar written in µM — the kind of value that shows up when assay sheets and stock-solution math collide on the same page.
Common mistakes
A decade lost among six zeros
Six places is more than the eye counts reliably, and the commonest error in this pair is a single misplaced decade: 5 µM written as 5 × 10⁻⁵ M rather than 5 × 10⁻⁶. Neither form looks wrong in a table of potency values. Convert by rewriting the exponent rather than by counting zeros, and sanity-check that a single- to triple-digit µM figure lands between 10⁻⁶ and 10⁻³ M.
Logarithmic quantities fed micromolar values
pH, pKa, pIC50 and pKd are all negative base-10 logarithms of a concentration in mol/L, so the conversion to M has to happen first. A compound active at 5 µM has a pIC50 of 5.30, from −log₁₀(5 × 10⁻⁶). Feeding the bare number 5 into the logarithm returns −0.70, and feeding 5 × 10⁻⁵ returns 4.30 — plausible-looking values that are simply the wrong compound.
Molarity treated as fixed with temperature
Both µM and M are per liter of solution, and solutions expand when warmed. Water alone loses about half a percent of its density between 20 °C and 37 °C, so a buffer prepared at the bench is slightly less concentrated once it reaches an incubator. The conversion factor is exact; the quantity it converts is temperature-dependent, which is the argument for molality wherever that matters.