Skip to main content

Millimolar to Micromolar Converter
↔ Convert µM to mM instead

Common Conversions

mM µM
0.001 1
0.005 5
0.01 10
0.05 50
0.1 100
0.25 250
0.5 500
1 1000
2 2000
5 5000
10 10000
100 100000

Why this conversion matters in chemistry

Multiplying by 1000 sounds like the kind of arithmetic that shouldn't deserve its own conversion page, and yet this is one of the most consequential factor-of-1000 errors in bench chemistry. Assay plates run at micromolar; substrate and cofactor concentrations are quoted in micromolar in the literature; but if you grab a 1 mM reading off a reagent label and treat it as 1 µM without thinking, your working concentration lands a thousand-fold too low and a reaction that should have gone in minutes doesn't detectably happen. A 1 mM ATP stock is 1000 µM — so a 100 µM working ATP in a kinase reaction takes 10 µL of stock per 100 µL of reaction, not the 100 µL you'd add if you confused the units.

Formula

µM = mM × 1000

Worked Examples

1 mM = 1000 µM

A standard ATP stock. Most kinase reactions pull from something close to this and dilute a hundred-fold into the working mix.

0.1 mM = 100 µM

A common substrate working concentration — roughly where many enzymes sit at or above their Km.

0.001 mM = 1 µM

The kind of IC50 you'd look at and think the inhibitor is worth developing further.

5 mM = 5000 µM

Fasting blood glucose in a healthy person is right around here — a useful mental anchor for the scale.

Frequently Asked Questions

How do I convert mM to µM?
Multiply by 1000. So 0.5 mM becomes 500 µM, and 2 mM becomes 2000 µM. The milli and micro prefixes are three orders of magnitude apart (10⁻³ and 10⁻⁶), so the factor is the same every time.
When is it natural to use mM versus µM?
Millimolar tends to show up for bulk things you prepare — buffer components, electrolyte concentrations, clinical metabolites. Micromolar is more common once you're dosing: drug IC50s, enzyme Km values, working-strength reagents. Most benches keep stocks in mM and do the division when they set up an experiment.
How do I prepare a µM solution from a mM stock?
C₁V₁ = C₂V₂ does all the work. For 10 mL of 100 µM from a 10 mM stock, you need (100 µM × 10 mL) / 10,000 µM = 0.1 mL of stock, topped up with diluent to 10 mL. Keeping everything in the same units before you start the arithmetic saves a surprising number of mistakes.
How do mM and µM fit into the full molarity scale?
1 M is 1000 mM, which is a million µM, which is a billion nM. So 1 mM is 10⁻³ M and 1 µM is 10⁻⁶ M. Each prefix is a clean factor of 1000 — the reason the scale is so forgiving to move around on once you're used to it.