# How to convert molar to millimolar?

Converts molar (M) to millimolar (mM) and back, with the exact unit definitions.

- Page: https://www.acalculator.org/convert/molar-to-millimolar
- JSON spec: https://www.acalculator.org/convert/molar-to-millimolar.json
- Version: 92b27fc600c4

## Default answer

Example with the default inputs (Molar (M) 1): 1 M = 1,000 mM.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| value | Molar (M) | The amount in molar to convert. |
| result | Millimolar (mM) | The same amount in millimolar. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| value | Molar (M) | The amount in molar to convert. |
| result | Millimolar (mM) | The amount in millimolar. |

## Method

mM = M × 1000 (the same as M ÷ 0.001)

## Assumptions

- 1 molar = 1000 millimolar, from the exact definitions in NIST SP 811.
- Exact on the typed decimals: at most 6 decimal places (6 significant digits below 0.0001), rounded half up.

## Worked examples

1. value = 1 gives result = 1,000. Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8.
2. value = 0.15 gives result = 150. Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8.
3. result = 150 gives value = 0.15. Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8.

## FAQ

### How many millimolar are in a molar?

1 molar is 1,000 millimolar, from the exact unit definitions (NIST SP 811).

### How do I convert molar to millimolar?

Multiply by 1,000: mM = M × 1000 (the same as M ÷ 0.001). For example, 1 M × 1,000 = 1,000 mM.

### How do I convert millimolar back to molar?

Multiply by 0.001, or type the millimolar into the second box and the converter works it out. 1 millimolar is 0.001 molar.

### What does molar (M) mean?

Moles of a substance per liter of solution: 1 M = 1 mol/L (IUPAC, amount concentration). Millimolar is a thousandth of that: 1 mM = 1 mmol/L.

### What is 0.15 M in mM?

0.15 × 1,000 = 150 mM. Normal saline (9 g of NaCl per liter) is about 0.154 M, or 154 mM.

### Do I need the molar mass?

No. M to mM only moves the decimal point three places. To go from grams per liter to molar you need the molar mass; the molarity calculator does that.

## Sources

- NIST SP 811 (2008), Guide for the Use of the International System of Units, Table 5 (SI prefixes) and Appendix B.8 (factors for units listed alphabetically), retrieved 2026-10-05. https://www.nist.gov/pml/special-publication-811
- IUPAC Compendium of Chemical Terminology (Gold Book), amount concentration: unit mol dm⁻³ or mol L⁻¹, sometimes written M, retrieved 2026-10-05. https://goldbook.iupac.org/terms/view/A00295