TRT Math: What mg/mL Actually Means (and How to Get Your Dose Right)

Concentration is a rate, not a total. Mixing that up is the single most common TRT arithmetic mistake, especially coming from peptides. One formula, worked examples, and a reference table.

When I switched from peptides to TRT, my first vial of testosterone cypionate almost got me. I’d run peptides for a couple of years, where the number on the vial is the total amount in it: a 5 mg BPC-157 vial holds 5 mg. So I read my testosterone label the same way, did the math, and it didn’t add up. Testosterone isn’t labeled by total. It’s labeled by concentration, in milligrams per milliliter, and reading the two the same way is the single most common mistake there is. It took me longer than I’d like to admit to untangle, mostly because I couldn’t find one place that just laid it out. So here it is.

Quick answer

Volume to draw (mL) = your dose (mg) ÷ the concentration on the vial (mg/mL). The concentration is a rate, not a total. A “250 mg/mL” vial does not contain 250 mg total unless it happens to be exactly 1 mL. Your dose itself is set by your prescriber; this is the arithmetic to turn that dose into a volume.

What “mg/mL” means

Concentration is how much testosterone is dissolved in every milliliter of oil in the vial. “200 mg/mL” means each milliliter you draw contains 200 mg. It is a rate, like miles per hour, not a fixed total. The same rate applies whether the vial is 1 mL or 10 mL; what changes with vial size is the total amount of testosterone in the whole container, not the concentration.

The mix-up this post exists to kill

Total mg in a vial is not the same number as the concentration on the label. A vial labeled “250 mg/mL” does not mean 250 mg total in the vial. Total mg = concentration × vial volume. A 10 mL vial at 250 mg/mL holds 2,500 mg total. This trips people up specifically because peptides are usually labeled by total mg in the vial (a “5 mg BPC-157 vial” really does mean 5 mg total), while injectable testosterone is labeled by concentration (mg/mL). Coming from peptides into TRT and reading the two labels the same way is exactly where this mistake happens.

The one formula

Everything below comes from a single relationship, rearranged:

Volume to draw (mL) = your dose (mg) ÷ concentration (mg/mL)

Divide the milligrams you need by the milligrams packed into each milliliter, and the result is the milliliters you draw. Everything else in this post (worked examples, the reference table, and splitting a weekly number across injections) is this same formula applied to different numbers.

Worked examples across common concentrations

Injectable testosterone ships at a handful of common concentrations: 100, 200, and 300 mg/mL are typical, and 250 mg/mL shows up often too. The same dose draws a different volume depending which one is on your vial:

200 mg ÷ 100 mg/mL = 2.0 mL
200 mg ÷ 200 mg/mL = 1.0 mL
200 mg ÷ 250 mg/mL = 0.8 mL
200 mg ÷ 300 mg/mL ≈ 0.67 mL

Same dose, four different volumes, because the concentration is different each time. A higher concentration always means a smaller volume for the same dose, and vice versa.

Reading it in syringe units

Standard insulin syringes are marked in units, where a U-100 syringe defines 100 units as 1 mL. So units = mL × 100. The 0.8 mL draw above is 80 units on a U-100 syringe. One gotcha worth flagging separately: “cc” (cubic centimeter) and “mL” are the same volume. Some syringes and older vial labels use “cc” instead of “mL,” and it is not a different unit that needs its own conversion.

Splitting a weekly number across injections

Most TRT protocols are prescribed as a weekly total, then split across two or more injections. To get from a weekly number to what you draw each time:

Per-shot dose (mg) = weekly dose (mg) ÷ injections per week, then apply the volume formula to that per-shot number.

Example: a 200 mg/week target, split into two injections (say, Monday and Thursday), is 100 mg per shot. At 200 mg/mL, that's 100 ÷ 200 = 0.5 mL per injection, or 50 units on a U-100 syringe.

Reference table: concentration × dose

Volume in mL, with syringe units in parentheses, for common per-injection doses:

Dose per injection	100 mg/mL	200 mg/mL	250 mg/mL	300 mg/mL
50 mg	0.50 mL (50u)	0.25 mL (25u)	0.20 mL (20u)	0.17 mL (17u)
100 mg	1.00 mL (100u)	0.50 mL (50u)	0.40 mL (40u)	0.33 mL (33u)
150 mg	1.50 mL (150u)	0.75 mL (75u)	0.60 mL (60u)	0.50 mL (50u)
200 mg	2.00 mL (200u)	1.00 mL (100u)	0.80 mL (80u)	0.67 mL (67u)
250 mg	2.50 mL (250u)	1.25 mL (125u)	1.00 mL (100u)	0.83 mL (83u)

mL needed for a 100 mg dose

Volume needed to draw a 100 mg dose at three common concentrations. Higher concentration, less volume, same dose.

How I run it now

My own protocol is 150 mg a week, split between Monday and Thursday, so 75 mg a shot (the tradeoffs of splitting a weekly dose into more or fewer shots are their own post, on injection frequency). Once the concentration math clicked, I’ve never drawn a wrong dose. But getting there meant cross-referencing three or four different sources until the numbers finally agreed, because I couldn’t find a single one that just laid it out. That is most of why this post exists.

Doing this without a doctor watching over your shoulder is stressful. I still get a flash of “did I get that right?” every time I draw. The arithmetic is one of the few parts you can make completely certain, so I made certain: I built this exact calculation into the app so I never have to trust my own math half-asleep before a shot. You can run it here for free too, in the Dosing Calculator's HRT tab. Give it your concentration and weekly dose and it returns the per-injection volume and syringe units, split across whatever frequency you inject on. It’s the same engine inside the app, so the numbers match what you see when you log a shot.

Frequently asked questions

What does "mg/mL" actually mean on a vial label?

It is a concentration: milligrams of testosterone dissolved in every one milliliter of oil. It is a rate, not a total amount in the vial. A "200 mg/mL" vial and a "100 mg/mL" vial can hold the exact same total mg if their volumes differ; the mg/mL number alone doesn't tell you how much is in the whole vial.

Does a 250 mg/mL vial contain 250 mg total?

Only if the vial happens to be exactly 1 mL. Total mg in the vial = concentration × vial volume. A 10 mL vial at 250 mg/mL holds 2,500 mg total, not 250 mg. This is the exact mix-up that trips people coming from peptides, which are usually labeled by total mg instead.

How do I convert my weekly dose into a per-injection volume?

Divide your weekly mg target by the number of injections per week to get the per-shot dose in mg, then divide that by your concentration in mg/mL to get the volume. A 200 mg/week target split into two injections is 100 mg per shot; at 200 mg/mL, that's 0.5 mL per injection.

Is "cc" the same as "mL"?

Yes. A cubic centimeter (cc) and a milliliter (mL) are the same volume, different names for it. Some syringes and older labels use "cc" instead of "mL." There is no conversion factor between them; you can read one as the other directly.

Can Stackeddd do this math for me?

Yes. The HRT tab of the Dosing Calculator takes your concentration and weekly (or per-injection) dose and returns the volume and syringe units automatically. This is the same engine used inside the Stackeddd app, so the numbers match what you see when you log a shot.

Sources

The arithmetic here is definitional: a concentration in mg/mL divided into a dose in mg gives a volume in mL. Every worked example on this page was re-checked against that relationship.
Depo-Testosterone (testosterone cypionate) prescribing information — the 100 mg/mL and 200 mg/mL strengths used in the examples are real labeled concentrations, not illustrative numbers. FDA.

This is educational information, not medical advice. Your dose is set by your prescribing physician. This post only explains the arithmetic for turning a prescribed dose into a volume to draw.