TRT 100mg Per Week: How Much to Draw Up (Worked Example)

100mg testosterone per week is how many ml?

The millilitres you draw depend entirely on the strength printed on the vial. The dose in milligrams stays the same; the volume changes because a stronger vial packs more milligrams into each millilitre. The formula is the same every time:

Volume (ml) = dose (mg) ÷ concentration (mg/ml)

Testosterone cypionate and enanthate for injection are most commonly supplied at 200mg/ml, and some compounded or international products are 250mg/ml. For a once-weekly 100mg dose:

• At 200mg/ml: 100 ÷ 200 = 0.5 ml
• At 250mg/ml: 100 ÷ 250 = 0.4 ml

So the same 100mg prescription is half a millilitre from a 200mg/ml vial and four-tenths of a millilitre from a 250mg/ml vial. If you are unsure why the volume moves, the relationship is explained in Dose vs Volume Explained and How mg/ml Works.

Converting ml to syringe units

Many people inject testosterone with a U-100 insulin syringe because the fine markings make a small volume easier to read. On a U-100 syringe, the scale runs 0 to 100 units across 1 ml, so 1 ml = 100 units and 0.1 ml = 10 units. To convert, multiply millilitres by 100:

The unit marks are a length scale on the barrel, not a measure of how much drug is present. The same 50-unit mark holds a different number of milligrams depending on vial strength. This is covered in U-100 Syringe Units Explained and What Are Syringe Units?.

Once-weekly: the full reference numbers

This table sets out the complete once-weekly draw for a fixed 100mg dose at both common strengths.

Read the strength off the label, not the box, and confirm it before every draw. A common error is assuming 200mg/ml when the vial is actually 250mg/ml, which would make 50 units deliver 125mg rather than 100mg.

Splitting 100mg into two injections a week

Some protocols split the weekly total into two smaller injections, for example every 3.5 days, rather than one larger weekly shot. Splitting does not change the weekly milligram total; it halves the amount per injection. For 100mg/week split into two, each injection is 50mg.

Run the same formula on the per-injection dose of 50mg:

• At 200mg/ml: 50 ÷ 200 = 0.25 ml = 25 units
• At 250mg/ml: 50 ÷ 250 = 0.20 ml = 20 units

Whether to split a dose is a clinical decision, not a maths one. The mechanics of splitting are described in What Is a Split Dose? and the timing options in Daily vs Twice Weekly vs Every 3.5 Days.

Once-weekly vs twice-weekly side by side

The table below shows both schedules so the per-injection draw is easy to compare. Note the weekly total is identical in every row.

A smaller per-injection volume is one reason some people report finding twice-weekly injections more comfortable, but comfort and absorption are individual and should be discussed with a prescriber.

Checking your numbers and avoiding errors

A quick way to sanity-check any draw is to multiply back: units ÷ 100 gives millilitres, and millilitres × concentration gives milligrams. If the result does not return your prescribed dose, recheck the strength you entered.

• Confirm vial strength first. 200mg/ml and 250mg/ml look similar on a label but change the draw by 20 percent.
• Match the syringe to the scale. The unit conversions here assume a U-100 syringe. A different syringe type may be marked only in millilitres.
• Account for the syringe you can read. A 0.5 ml or 1 ml insulin syringe shows these volumes clearly; the trade-offs are in 0.3ml vs 0.5ml vs 1ml Syringes.

To confirm the figures for your exact strength, enter your dose and vial concentration in the TRT dose calculator. This page is a measurement and education tool and does not recommend any dose; dosing decisions belong with a qualified prescriber.

FAQs