Unit Conversion Guide: mg, mcg, mL and Syringe Units

Most calculation errors come from units, not from the formulas. This guide shows the four conversions used on this site. It covers arithmetic only and is not medical advice.

1. Mass: mg and mcg

1 mg = 1000 mcg. To go from mg to mcg, multiply by 1000. To go from mcg to mg, divide by 1000. Examples: 2.5 mg = 2500 mcg; 250 mcg = 0.25 mg.

2. Concentration: mg/mL and mcg/mL

The same factor applies. 1 mg/mL = 1000 mcg/mL. So 2.5 mg/mL = 2500 mcg/mL.

3. Volume and syringe units

On a U-100 syringe, 100 units = 1 mL, so 1 unit = 0.01 mL. Units = mL × 100, and mL = units ÷ 100. Examples: 0.1 mL = 10 units; 25 units = 0.25 mL.

4. Syringe capacity

A 0.3 mL syringe holds 30 units, a 0.5 mL syringe holds 50 units, and a 1 mL syringe holds 100 units. A volume larger than the syringe cannot be measured in one draw.

Worked example (mathematical example only)

A vial of 5 mg in 2 mL is 2.5 mg/mL = 2500 mcg/mL. A target of 0.25 mg is 250 mcg. Volume = 250 ÷ 2500 = 0.1 mL = 10 units.

Common mistakes

Mixing mg and mcg in the same formula.
Treating syringe units as mL, or mL as units.
Assuming every syringe is U-100. These formulas are for U-100 only.

mg to mcg converter · mcg to mg converter · Syringe units calculator

Mathematical calculation only. Not medical advice.