A tuberculin syringes holds 1ml filled to the maximum. If you are using U-100 insulin, then
if you fill the TB syringe to the maximum, that is 100 units of insulin (100 units of insulin per ml of liquid
volume).
On some TB syringes I have, the first numbered mark is "0.1"....that' s 1/10th of a ml. And 0.1 ml of
U-100 insulin is 10 (ten) units of insulin.
I"M ASSUMING YOU ARE USING U-100 INSULIN !!!!! (If U-40 or U-50, these calculations will be different).
To get ONE unit of insulin in a TB syringe, remember that the very first mark next to the needle is "zero", then
each tiny little line is 0.01 ml or one unit of insulin, up to the first numbered mark (0.1ml), which is ten units of insulin.
It will be almost impossible to measure 1/2 unit of insulin in a TB syringe. You really need to get some insulin syringes.
The best for U-100 insulin are 3/10 cc capacity, 30 or 31 gauge, with 1/2-unit marks. Be sure to look at the
box of syringes for the words "1/2-unit marks" or something similar. Some pharmacists will insist that no such
thing exists, and will try to sell you syringes with 1/2cc capacity, instead. They are NOT the same thing.