What is the volume in milliliters (mL) equivalent to one unit of insulin, specifically U-100 (100 units per milliliter) insulin?

Insulin Unit to Volume Conversion

One unit of insulin is equal to 0.01 milliliters (mL) in standard U-100 insulin formulations. 1

Understanding Insulin Concentration

• Standard insulin concentration in the U.S. and most countries is U-100, which means 100 units of insulin per milliliter (100 units/mL) 2
• This standardized concentration means that 1 unit of insulin equals 0.01 mL of solution 1
• For example, 10 units of U-100 insulin equals 0.1 mL, and 50 units equals 0.5 mL 3

Special Insulin Formulations

• Concentrated insulin formulations have different unit-to-volume ratios:
  • U-500 insulin: 500 units/mL (1 unit = 0.002 mL) 2
  • U-300 insulin (Toujeo): 300 units/mL (1 unit = 0.0033 mL) 2
  • U-200 insulin: 200 units/mL (1 unit = 0.005 mL) 4

Clinical Implications

• Understanding the correct volume per unit is critical for:
  • Proper dosing when using syringes 3, 5
  • Interpreting insulin pump settings, which deliver precise volumes 3
  • Converting between different insulin concentrations 2

Accuracy Considerations

• At very low doses (1-2 units), accuracy becomes a significant concern:
  • Syringes have been shown to be less accurate than pens or pumps when delivering 1-2 units 3, 5
  • Studies show that 1-unit doses with standard syringes can have error rates of 23% 5
  • Doses below 2 units (0.02 mL) may have unacceptably large errors with standard syringes 6

Practical Applications

• When calculating insulin doses in clinical examples:
  • In basal-bolus regimens, the volume can be calculated by dividing the total units by 100 4
  • For example, 11 units of rapid-acting insulin equals 0.11 mL of U-100 insulin 4
• When transitioning between insulin concentrations:
  • Dose adjustments may be needed when switching between formulations 7, 8
  • The volume administered will change even if the unit dose remains the same 2

Common Pitfalls to Avoid

• Confusing different insulin concentrations can lead to serious dosing errors 2
• Using inappropriate devices for low-dose insulin administration can result in significant inaccuracy 3, 6
• When administering very small doses (<2 units), consider using insulin pens or pumps rather than syringes for greater accuracy 3, 5