How Are Insulin Syringes Calibrated?

U100 Syringe With Typical Orange Cap
U100 Syringe With Typical Orange Cap (Image: Image by, courtesy of Melissa Wiese)

Insulin, a human hormone, is taken by diabetics to control blood glucose levels. Insulin can not be swallowed because it will not survive digestion, and is most commonly injected subcutaneously (under the skin) in the abdomen.

Available in a number of strengths, it is very important to match the calibration of the syringe with the type of insulin you are taking. Incorrect dosages of insulin can lead to unconsciousness, coma and death.

Insulin Dose

Insulin is dosed in units, not by volume as most other drugs. Your health care provider will typically provide a dosage schedule of a certain number of units per day.

Insulin Strengths

There are three strengths of insulin typically available. They are U40, U100 and U500. Of these, U100 is the most commonly used for humans, while U40 is typically used in pets. U500 is used only for very high insulin doses.

The difference between these strengths is the number of units of insulin per milliliter (ml) of insulin liquid. U100 has 100 units of insulin per ml, while U40 contains only 40. U500, with 500 units of insulin per ml, allows high dosages to be given in a single injection.

These insulin ratings are independent of insulin types. All insulin types (long acting, short acting, etc.) are available in multiple strengths.

Matching the Syringe

One ml of insulin can contain a different number of units of insulin. Therefore insulin syringes must be matched to the insulin strength.

U100 syringes typically have an orange cap on the needle.

All insulin syringes will have their associated insulin type clearly marked on the barrel of the syringe. Insulin will also be clearly marked. Use only the proper syringe for the type insulin you are injecting.

Measuring the Injection

With the syringe and insulin properly matched, there is no conversion required. The numbers on the barrel of the syringe represent the number of units of insulin in that dose.


Injecting too little or too many units of insulin can have serious consequences.

The most commonly reported mishap occurs when humans and pets are being treated with different strengths of insulin at the same time.

Keep different insulin strengths and associated syringes separate, and inquire about color coded needles with your pharmacist.

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