# mcg, mg, mL, units and IU: what each one means

> The difference between micrograms, milligrams, millilitres, syringe units and international units, and how to convert between the ones that can be converted.

Source: https://peptidetracks.com/guides/mcg-mg-units-iu-explained
Last updated: 2026-10-08

**mcg and mg measure amount, mL measures volume, syringe units are a volume scale (100 units = 1 mL on a U-100 syringe), and IU measures biological activity.** You can convert mcg to mg directly. You can convert an amount to a volume only if you know the concentration. You cannot convert IU to mg without a factor specific to that substance.

## Amount: mcg and mg

| | Equals |
| --- | --- |
| 1 mg | 1,000 mcg |
| 0.5 mg | 500 mcg |
| 0.25 mg | 250 mcg |
| 0.1 mg | 100 mcg |

To go from mg to mcg, multiply by 1,000. To go from mcg to mg, divide by 1,000. The symbol µg means the same as mcg.

## Volume: mL and cc

A millilitre (mL) is a volume. 1 mL and 1 cc are the same thing.

## Syringe units

An insulin syringe is marked in units instead of millilitres. On a U-100 syringe:

| Units | Volume |
| --- | --- |
| 100 units | 1 mL |
| 50 units | 0.5 mL |
| 30 units | 0.3 mL |
| 10 units | 0.1 mL |
| 1 unit | 0.01 mL |

These units describe how much liquid is in the syringe. They say nothing about how much substance is in that liquid.

## Linking amount and volume: concentration

Concentration tells you how much substance is in each millilitre, for example 2.5 mg/mL.

- **Volume = amount ÷ concentration**
- **Amount = volume × concentration**

At 2.5 mg/mL (2,500 mcg/mL), 250 mcg is 250 ÷ 2,500 = 0.1 mL, which is 10 units. The [mcg to units converter](https://peptidetracks.com/tools/mcg-to-units-converter) does this in both directions.

## International units (IU)

An IU is a measure of biological effect, agreed separately for each substance. One IU of one substance is a different mass from one IU of another. Two consequences:

1. There is no general IU to mg conversion.
2. IU are not the same thing as the volume marks on a syringe. The exception is U-100 insulin itself, which the syringe was designed around.

If a label gives strength in IU, use the conversion supplied with that product or ask a pharmacist.

## The mix-ups to avoid

| Mix-up | Size of the error |
| --- | --- |
| mg read as mcg | 1,000 times |
| Syringe units read as mcg | Depends on concentration |
| mL read as units | 100 times |
| IU read as syringe units | Unpredictable |

Writing the unit next to every number in your log is the simplest protection. [PepVault](https://peptidetracks.com/features/dose-log) shows the unit on each entry.

## Common questions

### How many mcg are in a mg?

1,000.

### How many units is 0.5 mL?

50 units on a U-100 syringe.

### How many mcg is 10 units?

It depends on the concentration. Ten units is 0.1 mL, so it holds one tenth of the mcg/mL figure: 250 mcg at 2,500 mcg/mL, or 500 mcg at 5,000 mcg/mL.


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## About PepVault

PepVault is a free peptide tracker app for Android, iPhone, iPad and Mac. It keeps a personal log of doses, vial inventory, injection sites, schedules and reminders, body measurements and side effects, and exports the history as a CSV file.

- Website: https://peptidetracks.com
- Android (Google Play): https://play.google.com/store/apps/details?id=pepvault.peptide.tracker
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PepVault is for personal record keeping. It does not give medical advice or recommend doses.