Pedplot

TRT injection calculator

Converts a prescribed testosterone dose into mL and insulin-syringe units, and shows how long a vial lasts.

Unit conversion for the dose on your prescription. It does not suggest a dose.

Example values for the arithmetic only. Replace them with the numbers you want converted.

Per injection

0.5 mL

U-100 syringe

50 units

Per week

100 mg · 100 mg each

Vial lasts

20 injections · 140 days

See the curve Test C, 100 mg, Weekly.

By Austin Witherow and Mason Calvert · Last updated · Sources

How the conversion works

  • mL per injection = mg per injection ÷ concentration (mg/mL)
  • U-100 units = mL × 100
  • mg per week = mg per injection × injections per week
  • Injections per vial = vial mL × concentration ÷ mg per injection, rounded down to whole injections
  • Days a vial lasts = injections per vial × 7 ÷ injections per week

Example 1: 100 mg at 200 mg/mL is 0.5 mL, which is 50 units on a U-100 syringe. A 10 mL vial holds 20 of those injections, 140 days at once a week.

Example 2: 150 mg a week split into 2 injections at 250 mg/mL is 75 mg each, 0.3 mL or 30 units. A 5 mL vial holds 16 injections, 56 days.

Units are rounded to the nearest half unit, and mL is that unit count ÷ 100, so both show the same volume. The result may not land exactly on a syringe mark. A volume under 0.05 mL or over 3 mL gets a note to double-check the numbers entered.

Units vs mL

Insulin syringes are marked in units, not mL. On a U-100 syringe, 100 units is 1 mL (Humulin R label), so 1 unit is 0.01 mL. The units here are only a volume scale: they say nothing about the strength of the testosterone.

This conversion is for U-100 syringes only. Other scales exist, such as U-500 syringes made for concentrated insulin. Mixing scales changes the volume drawn: the Humulin R U-500 instructions warn that a U-100 syringe used with U-500 insulin can give 5 times the intended dose. Check the scale printed on the syringe.

Limits

  • This calculator converts the numbers you enter. It does not suggest a dose, and what anyone does with the result is their own decision.
  • The mg/mL on a vial counts the ester. PubChem's molecular weights put testosterone at 70% of testosterone cypionate (PubChem CID 441404), so 200 mg/mL of the ester is about 140 mg of testosterone per mL. See ester weight.
  • The days a vial lasts ignore what stays in the needle and the vial.

Questions

How many units is 100 mg of testosterone cypionate at 200 mg/mL?

0.5 mL, which is 50 units on a U-100 syringe. At 100 mg/mL the same 100 mg is 1 mL (100 units). See how the conversion works.

How many mL is 140 mg at 200 mg/mL?

0.7 mL, or 70 units on a U-100 syringe.

How long does a 10 mL vial last?

It depends on the dose and concentration. At 140 mg a week from a 200 mg/mL vial, it holds 14 whole injections, which is 98 days.

Is 1 unit the same as 1 mg?

No. A unit on a U-100 syringe is 0.01 mL. How many mg that holds depends on the concentration: at 200 mg/mL, 1 unit holds 2 mg. See units vs mL.

Sources

  1. FDA label. Humulin R (insulin human) FDA label, section 3: 100 units/mL (U-100); carton: Use only with a U-100 syringe
  2. FDA label. Humulin R U-500 FDA label, Instructions for Use: always inject with a U-500 syringe; using a U-100 syringe can give a 5 times overdose
  3. Computed (PubChem). PubChem, testosterone cypionate (CID 441404): molecular weight 412.6 g/mol; testosterone 288.4 g/mol (CID 6013)

The model and its limits are on the methodology page.