The one rule
The prefix "milli" means one thousandth and "micro" means one millionth, so one milligram is exactly 1,000 micrograms.[2] Everything else on this page follows from that.
Watch the symbolMicrograms are written mcg, µg or ug. In handwriting µg can be misread as mg, which is a thousandfold error. This site always writes "mcg" for that reason.
mg to mcg conversion chart
Multiply mg by 1,000 to get mcg; the chart lists the common values.
| mg | mcg |
|---|---|
| 0.01 mg | 10 mcg |
| 0.025 mg | 25 mcg |
| 0.05 mg | 50 mcg |
| 0.1 mg | 100 mcg |
| 0.125 mg | 125 mcg |
| 0.2 mg | 200 mcg |
| 0.25 mg | 250 mcg |
| 0.3 mg | 300 mcg |
| 0.5 mg | 500 mcg |
| 0.75 mg | 750 mcg |
| 1 mg | 1,000 mcg |
| 1.5 mg | 1,500 mcg |
| 2 mg | 2,000 mcg |
| 2.5 mg | 2,500 mcg |
| 5 mg | 5,000 mcg |
| 10 mg | 10,000 mcg |
How many mcg are in one unit?
On a U-100 insulin syringe, one unit is 0.01 mL.[1] So the micrograms in one unit depend only on the concentration of the solution:
| Concentration | mcg per unit | mcg per 10 units | Units per 100 mcg |
|---|---|---|---|
| 0.5 mg/mL | 5 | 50 | 20 |
| 1 mg/mL | 10 | 100 | 10 |
| 1.5 mg/mL | 15 | 150 | 6.67 |
| 2 mg/mL | 20 | 200 | 5 |
| 2.5 mg/mL | 25 | 250 | 4 |
| 3 mg/mL | 30 | 300 | 3.33 |
| 4 mg/mL | 40 | 400 | 2.5 |
| 5 mg/mL | 50 | 500 | 2 |
| 10 mg/mL | 100 | 1,000 | 1 |
Read it both ways. At 2.5 mg/mL one unit holds 25 mcg, so 100 mcg is 4 units. At 1 mg/mL one unit holds 10 mcg, so 100 mcg is 10 units.
Common vial and diluent pairs
If you know the vial size and the liquid added, find the concentration and the mcg in one unit here.
| Vial | 1 mL | 2 mL | 2.5 mL | 3 mL |
|---|---|---|---|---|
| 1 mg | 10 | 5 | 4 | 3.33 |
| 2 mg | 20 | 10 | 8 | 6.67 |
| 5 mg | 50 | 25 | 20 | 16.67 |
| 10 mg | 100 | 50 | 40 | 33.33 |
| 15 mg | 150 | 75 | 60 | 50 |
| 20 mg | 200 | 100 | 80 | 66.67 |
Values are mcg per unit on a U-100 syringe. A 5 mg vial with 2 mL of liquid holds 25 mcg in each unit.
Where mg and mcg get mixed up
Most mix-ups happen because labels and papers use different units.
- Labels and papers use different units. A vial may say "5 mg" while a study reports amounts in mcg or in mcg per kilogram of body weight.
- Per-kilogram amounts are not totals. "30 mcg/kg" means 30 mcg for every kilogram of body weight. It is not 30 mcg.
- International units (IU) are a different thing. IU measure biological activity and have no fixed conversion to mg. Syringe "units" are volume marks, not IU. The glossary defines each of these terms.
Keep going
- Peptide calculatorEnter your vial, diluent and amount in mcg
- Units chartsmcg amounts converted to syringe units
- Reconstitution guideHow the diluent volume sets mcg per unit
Frequently asked questions
How many mcg are in 1 mg?
1,000 mcg. So 0.25 mg is 250 mcg, and 2 mg is 2,000 mcg.
How many mg is 500 mcg?
0.5 mg. Divide micrograms by 1,000 to get milligrams.
How many mcg is 10 units of a peptide?
It depends on the concentration. 10 units is 0.1 mL. At 2.5 mg/mL that holds 250 mcg; at 5 mg/mL it holds 500 mcg. Multiply mg/mL by 100 to get the mcg in 10 units.
Is a syringe unit the same as an IU?
No. A unit on a U-100 syringe is a volume mark of 0.01 mL. An international unit (IU) measures biological activity and is defined separately for each substance.