mcg, mg, mL, units and IU: what each one means
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 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:
- There is no general IU to mg conversion.
- 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 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.
This guide is about record keeping and unit arithmetic. It is not medical advice. See the medical disclaimer.
