Last updated: May 2026
This guide covers how to calculate your testosterone dose, draw up correctly from any vial concentration, choose the right syringe and needle, inject safely, store your medication, and understand injection frequency. It is a mathematical and procedural reference — not medical advice. Always follow your prescriber's specific instructions.
Know your dose in mg? Use the TRT calculator to get your exact draw volume in mL and syringe units for any vial concentration.
Open TRT Calculator →Testosterone replacement therapy (TRT) is the medical treatment of hypogonadism — a condition where the body produces insufficient testosterone. It involves the administration of exogenous testosterone to restore levels to the physiological range. TRT is prescribed by a doctor following blood tests that confirm low testosterone, and the dose, ester, and injection schedule are determined by the prescriber based on clinical assessment.
TRT is not the same as anabolic steroid use for performance enhancement. Therapeutic doses are intended to bring testosterone into the normal physiological range — not above it. This guide deals exclusively with TRT as a prescribed medical treatment.
The most common forms of injectable TRT are testosterone cypionate and testosterone enanthate, both supplied as oil-based solutions in multi-dose vials. A vial label will state the concentration — most commonly 200 mg/mL in the United States, or 250 mg/mL for some international preparations. The number on your vial is critical: you need it to calculate every injection correctly.
Every testosterone vial has a concentration printed on the label — for example, 200 mg/mL. This means each millilitre of oil in the vial contains 200 mg of testosterone. The same dose in mg will require a different draw volume depending on this concentration.
Prescribed dose: 100 mg/week
200 mg/mL vial: 100 ÷ 200 = 0.5 mL
250 mg/mL vial: 100 ÷ 250 = 0.4 mL
Same dose. Different draw volumes. Always use your vial's label concentration.
Never assume a standard concentration. Compounding pharmacies in particular may supply testosterone at custom concentrations such as 100 mg/mL, 150 mg/mL, or 250 mg/mL. Check your vial label before every calculation. If the label is unclear, contact your pharmacy.
Converting a milligram dose to a millilitre draw volume is a single division:
Draw (mL) = Dose (mg) ÷ Concentration (mg/mL)
To convert millilitres to units on a U-100 insulin syringe, multiply by 100. This is because a U-100 syringe treats 1 unit as 0.01 mL.
Draw volume: 0.5 mL
0.5 mL × 100 = 50 units on a U-100 syringe
Use the TRT calculator to instantly convert any prescribed mg dose to your exact draw volume and syringe units.
TRT Dose Calculator →The table below shows draw volumes for the most common prescribed doses at typical vial concentrations. Use it as a quick reference — always verify using your specific vial label.
| 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) |
| 75 mg | 0.75 mL (75 U) | 0.38 mL (38 U) | 0.30 mL (30 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) |
Units shown are for U-100 syringes. If your syringe is a 1 mL standard syringe (not a U-100), the graduation marks are in tenths of a millilitre — read the mL column directly. If you are unsure which type of syringe you have, read the markings on the barrel: a U-100 insulin syringe labels up to 100 units; a 1 mL standard syringe labels up to 1.0 mL.
TRT doses are often split across multiple injections per week rather than given as a single weekly injection. Splitting your weekly dose into smaller, more frequent injections produces more stable testosterone blood levels over time — smaller peaks and higher troughs — which many patients find reduces side effects such as mood swings, elevated haematocrit, and oestradiol fluctuations.
| Schedule | Example | Notes |
|---|---|---|
| Once weekly | 100 mg every 7 days | Simple. Wider peaks and troughs. |
| Twice weekly | 50 mg every 3.5 days | More stable levels. Common protocol. |
| Every other day (EOD) | ~33 mg every 2 days | Most stable. Good for short esters. |
| Daily | ~14 mg daily | Very stable. Typically subcutaneous. |
If your prescriber has given you a weekly dose and you inject twice weekly, each injection is half the weekly dose. For example, 100 mg/week split twice weekly = 50 mg per injection. The InjectBuddy EOD calculator helps you calculate per-injection volumes for every-other-day protocols.
Injecting every other day? The EOD calculator splits your weekly dose and gives you the exact draw volume per injection.
EOD Calculator →Two types of syringes are commonly used for TRT: U-100 insulin syringes and standard 1 mL or 3 mL syringes. The right choice depends on your draw volume, injection route (intramuscular or subcutaneous), and personal preference.
U-100 insulin syringes are available in 0.3 mL (30 units), 0.5 mL (50 units), and 1 mL (100 units) barrel sizes. They come with ultra-fine attached needles (typically 28–31 gauge, 8–12.7 mm) that make them well-suited for subcutaneous injections. The main advantage is minimal dead space — very little medication is left in the hub after injection. The main limitation is that for intramuscular injections, the attached needle may be too short to reliably reach muscle in all body areas.
Standard 1 mL and 3 mL syringes with a Luer-lock or slip-tip allow you to attach separate needles. A common TRT practice is to draw using a larger needle (18–21 gauge) to pull the thick oil through quickly, then swap to a smaller injection needle (23–25 gauge, 1–1.5 inch) for the actual injection. This approach is particularly useful for intramuscular injections into the glute or thigh where a longer needle is needed to penetrate adequately.
| Injection Type | Site | Gauge | Length |
|---|---|---|---|
| Intramuscular (IM) | Glute | 23–25G | 1–1.5 inch |
| Intramuscular (IM) | Outer thigh (vastus lateralis) | 23–25G | 1–1.5 inch |
| Subcutaneous (SubQ) | Abdomen / love handle | 27–29G | 0.5–1 inch |
| Subcutaneous (SubQ) | Upper outer thigh | 27–29G | 0.5–1 inch |
Gauge refers to needle diameter: a higher number means a thinner needle. Thinner needles (higher gauge) cause less discomfort but draw thick oil more slowly. Shorter needles reduce how deep the injection goes. Your prescriber or pharmacist will recommend the appropriate gauge and length for your injection method and body composition.
Testosterone can be administered either intramuscularly (into muscle) or subcutaneously (into the fat layer beneath the skin). Both routes deliver the medication into the body effectively, though with slightly different absorption characteristics.
The traditional and most studied route for testosterone. IM injections deposit the oil into muscle tissue, where it is absorbed into the bloodstream from the oil depot. Common IM sites for TRT are the gluteus medius (upper outer quadrant of the buttock), the vastus lateralis (outer thigh), and the deltoid (upper arm). Peak absorption tends to be faster than subcutaneous.
SubQ injections deposit the oil into the fat layer just beneath the skin. The absorption is generally slower and the resulting testosterone peak is lower and broader compared to IM. Many patients on daily or every-other-day protocols prefer SubQ because it is easier to self-administer, causes less discomfort, and uses shorter finer needles. Some patients also report lower oestradiol levels with SubQ, though this is not universally observed.
Both routes are used in clinical practice. Your prescriber will specify which route to use. Do not switch injection routes without medical guidance, as pharmacokinetics differ and your blood level targets may need to be reassessed.
Testosterone is supplied as an oil-based solution. Oil is thicker than water and requires a few extra steps to draw accurately.
Rotating injection sites between and within areas is essential to prevent the formation of scar tissue, lipohypertrophy (lumpy fat under the skin), and localised pain. Repeatedly injecting into the same small area causes the tissue to thicken, which impairs absorption and causes discomfort.
If you inject twice weekly, alternate between two distinct sites — for example, left glute Monday, right glute Thursday. If you inject more frequently (EOD or daily), map out a rotation across four or more sites: both glutes, both thighs, and optionally both deltoids or abdomen. Allow each site at least 7 days of recovery before reusing it.
Avoid injecting into skin that is bruised, tender, has active lumps or hardness, is infected, scarred, or covered by a rash. If you notice persistent hardness, swelling, warmth, or redness at a site, contact your prescriber.
Some discomfort during and after TRT injections is normal, particularly in the first few weeks. Several practical steps can reduce pain:
If you experience severe, spreading pain, significant swelling, fever, or discharge at an injection site, seek medical attention promptly — these may indicate infection.
A small amount of oil tracking back up the needle channel and appearing on the skin surface after an IM injection is common, especially with thicker oil bases. This can mean a small amount of medication is lost. The Z-track technique — pulling the skin slightly to one side before injecting and releasing after withdrawal — helps seal the needle track and prevents this leakback. Pausing 3–5 seconds after fully depressing the plunger before withdrawing also allows the oil to disperse away from the needle tip.
Injectable testosterone cypionate and enanthate are stored at controlled room temperature. The typical storage recommendation is 20–25°C (68–77°F), protected from light and moisture. Keep the vial in its original carton when not in use.
If your oil has changed colour significantly (beyond the pale yellow that is normal for testosterone oil), contains visible particles that do not clear on warming, or appears separated or chunky, do not use it — contact your pharmacy.
When travelling, keep your testosterone vial and syringes in your carry-on bag (with airline size restrictions in mind for liquids) or in a secure bag in your checked luggage — check airline and destination country regulations in advance. Carry your prescription documentation and pharmacy label with the vial. At airport security, declare your medication and syringes. Most countries with a valid prescription allow personal-use quantities of testosterone for medical travellers, but requirements vary — research the specific rules for your destination.
Testosterone vials should not be left in a hot car or exposed to excessive heat during travel. Carry them in an insulated bag if ambient temperatures are likely to exceed 30°C (86°F) for extended periods.
This guide is a mathematical and procedural reference only. It is not medical advice. TRT is a prescription treatment — doses, esters, injection routes, frequency, and monitoring are determined by a licensed prescriber based on individual clinical assessment and blood test results. Do not self-prescribe, adjust your dose, or change your injection schedule without medical guidance. Always follow your prescriber's specific instructions. If you experience adverse effects, contact your healthcare provider promptly.
The clinical pharmacokinetics of testosterone esters cited in this guide are consistent with the published prescribing information for testosterone cypionate and testosterone enanthate. The Endocrine Society's Clinical Practice Guideline for Testosterone Therapy in Men with Hypogonadism (2018) provides the clinical framework for TRT prescribing. Injection technique guidance is consistent with standard clinical nursing and pharmacy references.
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.