Insulin is a hormone that helps regulate blood sugar levels. For people with diabetes who require insulin injections, it is important to understand the relationship between insulin units and volume. This allows proper dosing of insulin for optimal blood sugar control.
The Short Answer
The short answer is:
1 mL of insulin contains 100 units of insulin.
So if someone’s insulin dose is 25 units, they would need to inject 0.25 mL of insulin to get that dose. The concentration of most insulin preparations is 100 units/mL (U-100).
What is Insulin?
Insulin is a hormone made by the pancreas that allows cells throughout the body to use glucose (sugar) for energy. Insulin helps move glucose from the blood into cells. When insulin is absent or cells become resistant to its effects, blood glucose levels rise resulting in diabetes.
People with type 1 diabetes don’t make any insulin at all. People with type 2 diabetes don’t make enough insulin or are insulin resistant. For these individuals, injecting insulin is necessary to regulate blood sugar. Insulin therapy replaces or supplements the body’s own insulin.
Types of Insulin
There are several types of insulin preparations available:
- Rapid-acting insulin – Starts working within 15 minutes, peaks in about 1 hour, and continues working for 2 to 4 hours.
- Short-acting insulin – Takes effect within 30 minutes, peaks in 2 to 3 hours, and lasts for 3 to 6 hours.
- Intermediate-acting insulin – Starts working in 1 to 3 hours, peaks 4 to 12 hours later, and lasts for up to 18 hours.
- Long-acting insulin – Takes 3 to 4 hours to start working, has no peak, and lasts up to 24 hours.
- Pre-mixed insulin – Combinations of rapid or short-acting insulin mixed with intermediate insulin.
The concentration of insulin is measured in units per milliliter (U/mL).
In the United States, most insulin preparations are U-100 insulins. This means there are 100 units of insulin in every 1 mL (100 U/mL).
The concentration of insulin may be different outside the US. For example, U-40 (40 units per mL) and U-500 (500 units per mL) insulin preparations are also available.
Insulin dosing is based on a person’s individual needs and prescribed in units. Common dosing for those with diabetes involves:
- Basal insulin – Long-acting insulin taken once or twice per day to maintain baseline blood sugar control.
- Bolus insulin – Rapid or short-acting insulin taken with meals to handle rises in blood sugar from carbohydrate intake.
For U-100 insulin, each 1 unit decrease in blood sugar is expected with every 1 unit injected. This 1:1 ratio allows easy conversion from prescribed insulin dose to volume required for injection.
For example, if a person’s prescribed insulin dose is 25 units, they would need 25 units/100 units per mL = 0.25 mL of U-100 insulin.
Common Insulin Doses
Some typical U-100 insulin doses and their corresponding volumes include:
|Prescribed Insulin Dose||Volume Needed|
|10 units||0.1 mL|
|15 units||0.15 mL|
|20 units||0.2 mL|
|25 units||0.25 mL|
|30 units||0.3 mL|
|35 units||0.35 mL|
|40 units||0.4 mL|
|45 units||0.45 mL|
|50 units||0.5 mL|
Insulin Pens, Syringes, and Pumps
Insulin is most commonly injected using:
- Syringes – Allow measurement of any insulin dose. Needle attaches directly to the syringe.
- Pens – Pre-filled with insulin and allow easy injection of common doses. Needle attaches to the pen.
- Pumps – Continuously deliver insulin throughout the day via a catheter placed under the skin. Allow programming of complex basal/bolus dosing.
Syringes are available with different graduations depending on the type of insulin used:
- U-100 syringes – Graduated every 1 unit up to 100 units.
- U-40 syringes – Graduated every 0.5 units up to 40 units.
- U-500 syringes – Graduated every 5 units up to 500 units.
Using the correctly graduated syringe is important to accurately measure and deliver small insulin doses.
Reading an Insulin Syringe
Insulin syringes have three parts:
- The needle attaches to the syringe barrel.
- The plunger is pulled to draw insulin into the barrel.
- Markings on the barrel indicate the insulin volume in units.
To read an insulin syringe:
- The syringe should be held with the needle pointing upwards.
- The marking on the plunger indicates the insulin volume drawn up.
- The line on the plunger is aligned with the marking on the syringe barrel to read the volume.
Drawing Up Insulin
To draw insulin into a syringe, these general steps are followed:
- Attach the needle to the syringe tip.
- Pull the plunger down to draw air into the syringe equivalent to the insulin dose.
- Inject air into the insulin vial and invert the vial.
- With the needle in the vial, slowly pull back the plunger to withdraw the prescribed insulin volume.
- Before removing the needle, check for air bubbles and tap them out.
- Confirm the correct volume by reading the marking on the plunger.
Adjusting Insulin Doses
Healthcare providers may adjust insulin doses based on an individual’s blood sugar trends and hemoglobin A1C levels. Reasons for dose adjustments include:
- Starting insulin therapy or changing the regimen
- Loss of blood sugar control or running persistently high/low
- Changes in diet, physical activity, medications, or health status
- Preparing for sick days or procedures
- During growth phases like puberty
- During pregnancy or lactation
Small, incremental dose changes are often made weekly until blood sugar targets are achieved. Larger dose changes may be warranted with significant lifestyle modifications or rapidly worsening control.
Example Insulin Dose Adjustments
|Original Dose||New Dose||Volume Change|
|10 units||12 units||+ 0.02 mL|
|25 units||22 units||– 0.03 mL|
|50 units||56 units||+ 0.06 mL|
- The standard insulin concentration is 100 units per 1 mL (U-100).
- Dosing is based on prescribed units of insulin, then converted to volume for injection.
- With U-100 insulin, 25 units requires 0.25 mL, 50 units is 0.5 mL, etc.
- Proper measuring devices (syringes, pens) must be used to accurately draw up and inject doses.
- Insulin doses are adjusted periodically based on an individual’s blood sugar trends.
The Bottom Line
For standard U-100 insulin preparations:
1 mL of insulin contains 100 units.
Knowing the units-to-milliliter relationship allows people with diabetes to accurately dose insulin for optimal blood sugar management. Proper education, measurement tools, and dose adjustments over time help ensure safe and effective insulin use.