There are two types of Humulin R insulin available: Humulin R U-100 and Humulin R U-500.
Humulin R U-100:

• Humulin R U-100 contains 100 units of insulin in each 1 mL of liquid.
• It comes in two vial sizes:
• A 3 mL vial contains 300 units of insulin.
• A 10 mL vial contains 1,000 units of insulin.

Humulin R U-500:

• Humulin R U-500 contains 500 units of insulin in each 1 mL of liquid.
• It is available in a 20 mL vial, which contains a total of 10,000 units of insulin.

So, in simple terms, there are two strengths of Humulin R insulin: U-100 and U-500. U-100 comes in 3 mL and 10 mL vials, while U-500 comes in a 20 mL vial. Each vial contains a specific amount of insulin, either 100 units per 1 mL or 500 units per 1 mL, depending on the type of insulin and vial size.