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Micromolar to Millimolar Converter
↔ Convert mM to µM instead

Common Conversions

µM mM
1 0.001
5 0.005
10 0.01
25 0.025
50 0.05
100 0.1
250 0.25
500 0.5
1000 1
2000 2
5000 5
10000 10

Why this conversion matters in chemistry

Stock bottles and working plates rarely share units, and that's most of the story here. A reagent gets prepared at millimolar for shelf stability, then diluted into the assay at micromolar — and somewhere in between, every protocol sheet has to reconcile the two. For 500 µM EDTA in a buffer, that's 0.5 mM, which tells you to pull a thousand-fold dilution from the 500 mM master stock. The arithmetic is dividing by 1000, but the real value is developing the reflex to convert without thinking, because you'll do it two or three times before a single experiment starts.

Formula

mM = µM / 1000

Worked Examples

500 µM = 0.5 mM

Common EDTA concentration in a chelation buffer — enough to lock up divalent cations without interfering with most downstream assays.

1000 µM = 1 mM

A clean round number where a lot of enzyme substrates end up at saturation.

100 µM = 0.1 mM

Working range for many fluorescent probes in live-cell imaging — bright enough to detect, dilute enough not to perturb.

50 µM = 0.05 mM

Roughly the free calcium concentration you'd see in a briefly stimulated cell. Not something you prepare — something you measure.

Frequently Asked Questions

How do I convert µM to mM?
Divide by 1000. One millimolar is exactly a thousand micromolar, so 2500 µM simplifies to 2.5 mM. It's one of the conversions where the arithmetic is genuinely trivial — the mental load is remembering which direction you're going.
When does this conversion come up in practice?
Mostly when tying together two halves of the same experiment: an assay concentration that's expressed in µM and a stock bottle labeled in mM. Also common when preparing a dilution series and trying to work out how many thousand-fold steps you need.
How do I figure out how much to weigh for a mM solution?
The working formula is mass (mg) = concentration (mM) × volume (mL) × MW (g/mol) / 1000. For 100 mL of 2.5 mM NaCl (MW 58.44), that's 2.5 × 100 × 58.44 / 1000, which works out to 14.6 mg. For bigger volumes or higher concentrations the number scales linearly, which is why it's worth getting comfortable with the structure.
What's the full molarity prefix ladder?
M → mM → µM → nM → pM → fM, each step a factor of 1000. That's mol/L, 10⁻³, 10⁻⁶, 10⁻⁹, 10⁻¹², 10⁻¹⁵ respectively. Most benchwork happens somewhere in the mM to nM band; the ends of the ladder show up mostly in trace analysis (fM) or macromolecule storage (M).