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What is testosterone (TRT)? a plain-English guide to dosing
Testosterone (TRT) is a prescribed treatment that adds testosterone back when your body does not make enough — a condition called hypogonadism confirmed by blood tests — with the aim of restoring testosterone to the normal physiological range, not above it. It is most commonly given as a weekly or twice-weekly oil-based injection of testosterone cypionate or enanthate. This guide explains the common esters and injection schedules, works through the maths that converts an mg dose and vial concentration into a syringe draw, and answers the questions people ask most.
Key takeaways. TRT restores low testosterone to normal range. Draw (mL) = dose (mg) ÷ vial mg/mL; units = mL × 100 on a U-100 syringe. Splitting the weekly dose steadies blood levels. Know your vial’s concentration before every injection — the calculator does the arithmetic for you.
Open TRT Calculator →What TRT is — and is not
TRT replaces a hormone the body is no longer making in sufficient amounts. It is diagnosed from a low morning total-testosterone reading (usually confirmed on two separate tests) alongside symptoms, and the Endocrine Society recommends treating only when both are present. It is not the same as supraphysiological steroid use for performance: therapeutic dosing targets the middle of the normal range, typically 100–200 mg of testosterone per week for men, often split into smaller injections.
The two injectable esters you will see most are cypionate (standard in North America) and enanthate (common internationally). An “ester” is a fatty chain bolted onto the testosterone molecule that slows its release from the oil depot — longer chains release more slowly, which is why these are dosed weekly rather than daily. Both arrive as oil in a multi-dose vial with a concentration printed on the label.
If you are about to start, the starting TRT practical checklist covers baseline labs, supplies and your first dose in order.
Testosterone reference ranges in ng/dL and nmol/L
Testosterone results are usually reported as total testosterone, and the number depends on the laboratory method, time of collection, and reference interval used by that lab. The values below reproduce one commonly cited adult male interval from the source guide; they are reference points, not treatment targets or a diagnosis. A result should be read alongside symptoms, repeat morning testing, the laboratory's own interval, and a prescriber's assessment.
| Percentile | Total testosterone (ng/dL) | Total testosterone (nmol/L) |
|---|---|---|
| 2.5th | 264 | 9.2 |
| 5th | 303 | 10.5 |
| 50th | 531 | 18.4 |
| 95th | 852 | 29.5 |
| 97.5th | 916 | 31.8 |
To compare units, divide ng/dL by 28.84 to get nmol/L; rounding to one decimal place explains small differences between displayed values. For example, 852 ng/dL is about 29.54 nmol/L, displayed as 29.5. The conversion changes units only. It does not change the underlying result or tell you whether treatment is appropriate.
Reference intervals differ among laboratories and populations. Total testosterone can also vary from one day to another, so clinicians interpret it with the collection time, health context, symptoms, and repeat measurements. Free testosterone and sex hormone-binding globulin may be considered when total testosterone does not fit the clinical picture, but they are separate measurements with their own methods and ranges. Do not compare a result directly with a range printed by a different laboratory without checking the units and assay.
A number near the low end is not by itself a diagnosis, and a number inside a listed interval does not rule out every cause of symptoms. The Endocrine Society guideline describes diagnosis as symptoms or signs together with consistently low concentrations, confirmed with repeat morning fasting measurements. Use the interval supplied with your lab report and discuss results with your prescriber.
Why the vial concentration drives everything
Every testosterone vial states a concentration such as 200 mg/mL — each milliliter of oil holds 200 mg of testosterone. The Depo-Testosterone label, for instance, is supplied as both 100 mg/mL and 200 mg/mL. The same prescribed mg can therefore mean very different volumes in the syringe, so the label number is non-negotiable.
Dose: 100 mg/week
On 200 mg/mL: 100 ÷ 200 = 0.50 mL
On 250 mg/mL: 100 ÷ 250 = 0.40 mL
Same dose, different draw. Always use your label’s mg/mL.
How this is calculated
Converting a milligram dose to a syringe reading is two steps of arithmetic. First divide, then scale to units:
Draw (mL) = Dose (mg) ÷ Concentration (mg/mL)
Units on a U-100 syringe = Draw (mL) × 100 (because 1 unit = 0.01 mL)
100 ÷ 200 = 0.50 mL; 0.50 × 100 = 50 units
Half a milliliter, half a 1 mL insulin syringe.
50 mg per shot on 200 mg/mL: 50 ÷ 200 = 0.25 mL
0.25 mL = 25 units, twice a week.
200 ÷ 250 = 0.80 mL; 0.80 × 100 = 80 units
A single weekly shot of 0.8 mL.
Common dose reference chart
Draw volumes (and U-100 units) for typical weekly doses at the three concentrations you are most likely to be handed. Verify against your own vial.
| Dose | 100 mg/mL | 200 mg/mL | 250 mg/mL |
|---|---|---|---|
| 50 mg | 0.50 mL (50 U) | 0.25 mL (25 U) | 0.20 mL (20 U) |
| 100 mg | 1.00 mL (100 U) | 0.50 mL (50 U) | 0.40 mL (40 U) |
| 125 mg | 1.25 mL (125 U) | 0.63 mL (63 U) | 0.50 mL (50 U) |
| 150 mg | 1.50 mL (150 U) | 0.75 mL (75 U) | 0.60 mL (60 U) |
| 200 mg | 2.00 mL (200 U) | 1.00 mL (100 U) | 0.80 mL (80 U) |
Injection frequency: why splitting helps
A long-ester oil shot peaks a day or two after injection, then tapers until the next one. Inject the whole week’s dose at once and you get a bigger peak and a lower trough; split it into smaller, more frequent shots and the line flattens. Steadier levels are why many protocols favor twice-weekly or every-other-day dosing, and a study of subcutaneous testosterone found total and free testosterone stayed within the normal range between injections.
| Schedule | Example (100 mg/wk) | Trade-off |
|---|---|---|
| Once weekly | 100 mg every 7 days | Simplest; widest peaks/troughs. |
| Twice weekly | 50 mg every 3.5 days | Common; noticeably steadier. |
| Every other day | ~29 mg every 2 days | Very steady; more injections. |
| Daily | ~14 mg daily | Steadiest; usually subcutaneous. |
100 mg ÷ 3.5 shots/week ≈ 29 mg per every-other-day shot
On 200 mg/mL: 29 ÷ 200 ≈ 0.145 mL ≈ 15 units.
Injecting every other day or every 3.5 days? The TRT calculator splits your weekly dose and returns the exact per-shot draw.
TRT & EOD Calculator →IM vs subcutaneous, and needle choice
Testosterone can go intramuscular (into muscle — glute, vastus lateralis, deltoid) or subcutaneous (into the fat layer). Both work; SubQ tends to give a lower, broader peak and lets you use a shorter, finer needle, which is why daily and EOD users often prefer it. Your prescriber specifies the route — don’t switch without guidance, as your level targets may need re-checking.
| Route | Typical site | Gauge | Length |
|---|---|---|---|
| IM | Glute / outer thigh | 23–25G | 1–1.5 in |
| SubQ | Abdomen / upper thigh | 27–29G | 0.5–1 in |
| Draw needle | (drawing thick oil only) | 18–21G | 1–1.5 in |
A common practice is to draw the thick oil quickly with an 18–21G needle, then swap to a finer one to inject. Higher gauge = thinner needle = less discomfort but slower draw. Never reuse a needle: single-use is the basic rule of safe injection.
If ~0.05 mL of oil stays in the needle hub each shot, that’s 0.05 × 200 = 10 mg lost per injection on a 200 mg/mL vial.
Low-dead-space insulin syringes minimize this.
10 mL × 200 mg/mL = 2000 mg. At 100 mg/week: 2000 ÷ 100 = 20 weeks.
Roughly five months from one vial.
Storing your vial
Per the prescribing label, store testosterone cypionate at controlled room temperature, 20–25°C (68–77°F), and protect it from light. Don’t refrigerate (cold oil turns cloudy and thick) or freeze it, and keep it in its carton. If the oil shows particles that don’t clear on warming, or an off color, don’t use it — ask your pharmacy.
Medical disclaimer
This guide is a maths and procedural reference and does not constitute medical advice. TRT is a prescription treatment: dose, ester, route, frequency, and monitoring are set by a licensed prescriber from your individual assessment and bloodwork. Do not self-prescribe or change your protocol without medical guidance, and contact your provider about any adverse effects.
So, what is testosterone (TRT)?
TRT is a prescribed therapy that restores testosterone to the normal physiological range when a person's body cannot produce enough on its own — confirmed by blood tests showing low levels alongside symptoms. The standard injectable form uses long-acting oil-based esters (cypionate or enanthate), and the dose-to-draw formula is straightforward: draw (mL) = dose (mg) divided by concentration (mg/mL), then multiply by 100 for U-100 syringe units. For the quickest result, enter your dose and vial strength into the TRT dose calculator.
Frequently asked questions
What is testosterone (TRT)?
How do I calculate my TRT draw from a vial?
What is the difference between cypionate and enanthate?
How often should I inject testosterone?
Can testosterone be injected subcutaneously instead of intramuscularly?
Sources
- Travison TG, et al. Harmonized Reference Ranges for Circulating Testosterone Levels in Men of Four Cohort Studies. J Clin Endocrinol Metab. 2017.
- Bhasin S, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2018;103(5):1715–1744.
- DailyMed, U.S. National Library of Medicine. Depo-Testosterone (testosterone cypionate injection) prescribing information — concentration and storage.
- McFarland J, et al. Serum Testosterone Concentrations Remain Stable Between Injections in Patients Receiving Subcutaneous Testosterone. J Endocr Soc. 2017;1(8):1095–1103.
- Campbell K, et al. Safety Aspects and Rational Use of Testosterone Undecanoate in the Treatment of Testosterone Deficiency. Drug Healthc Patient Saf. 2023;15:73–84.
- Centers for Disease Control and Prevention. Safe Injection Practices and Your Health. CDC, 2024.
- Mulhall JP, et al. Evaluation and Management of Testosterone Deficiency: AUA Guideline. J Urol. 2018;200(2):423–432.
- Sizar O, Schwartz J. Male Hypogonadism. StatPearls, NCBI Bookshelf. Updated 2023.
- Patel P, et al. Androgen Replacement. StatPearls, NCBI Bookshelf. Updated 2023.
- Schulte-Beerbühl M, Nieschlag E. Hormone kinetics after intramuscular testosterone cypionate (peak-and-trough release of the long-acting ester). Acta Endocrinol (Copenh). 1987;114(4):485–489.
- Wilson DM, et al. Pharmacokinetics, safety, and patient acceptability of subcutaneous versus intramuscular testosterone injection. Clin Ther. 2018;40(1):16–22.
- U.S. Food and Drug Administration. FDA issues class-wide labeling changes for testosterone products (approved use is treatment of confirmed hypogonadism). FDA, 2025.