TRT Dose Conversion for UK Patients: mL, mg, and Insulin Syringe Math

UK private TRT prescriptions almost always come in mg per week. UK testosterone vials (Sustanon 250, testosterone enanthate, testosterone cypionate) are labelled in mg/mL. And UK pharmacies typically issue 1 mL or insulin syringes marked in units, not mL. Three different units, one dose. This guide handles the conversions.

The Three Numbers You Need

1. Weekly mg: what your prescriber wrote on the script (e.g., 150 mg per week)
2. mg/mL: the concentration printed on the vial (Sustanon 250 = 250 mg/mL; testosterone enanthate is commonly 250 mg/mL in UK private prescribing)
3. Injection frequency: once weekly, twice weekly, every 3.5 days, or daily (microdosing)

0.5 mL of Testosterone Cypionate: How Much Is That in mg?

This is the most common UK Google search in this space. The answer depends on the concentration:

So if your UK private prescription is 100 mg/week of testosterone cypionate and you have a 200 mg/mL vial, that's 0.5 mL once weekly. Same dose at 250 mg/mL would be 0.4 mL once weekly.

0.25 mL on a 1 mL Syringe: Where Does That Mark Sit?

A standard 1 mL insulin or sub-Q syringe is marked in units (0 to 100). The conversion is direct:

• 0.1 mL = 10 units
• 0.15 mL = 15 units
• 0.2 mL = 20 units
• 0.25 mL = 25 units
• 0.3 mL = 30 units
• 0.5 mL = 50 units
• 1.0 mL = 100 units

So "0.25 mL on a 1 mL syringe" sits at the 25-unit mark, exactly one-quarter of the way up.

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1 mL of Testosterone Per Week: How Much Is That?

Again, depends on concentration:

250 mg/week is on the higher end for TRT and is more typical of optimised private TRT protocols (e.g., Mansmatters, Optimale, ConsultantCare) than NHS prescribing, which typically targets 100 to 150 mg per week.

Daily Microdosing: 0.15 mL Per Day Math

Daily microdosing splits the weekly dose across seven days. If your prescription is 140 mg/week:

• Weekly mg ÷ 7 days = daily mg → 140 ÷ 7 = 20 mg/day
• Daily mg ÷ concentration = daily mL → 20 ÷ 200 = 0.10 mL/day at 200 mg/mL
• Or 20 ÷ 100 = 0.20 mL/day at 100 mg/mL

A daily 0.15 mL injection at 200 mg/mL = 30 mg/day = 210 mg/week (closer to high-end TRT). Most UK daily microdose protocols sit between 0.07 mL and 0.15 mL per day.

200 mg of Testosterone Per Week, Split Daily: Insulin Syringe Math

This query appears in UK long-tail repeatedly. Here's the math at the common UK concentrations:

(200 ÷ 7 = 28.57 mg per day. Round to your preferred precision.)

Injection Frequency: Every 3 Days vs 7 Days vs 14 Days

Testosterone esters have different half-lives. Frequency affects how flat or peaky your blood levels are between injections:

NHS prescribing has historically defaulted to every 14 days for Sustanon 250 or testosterone enanthate. Most UK private TRT clinics now prescribe once or twice weekly because the blood-level swings on 14-day Sustanon are too large for many patients to tolerate.

Going from every 14 days to twice weekly does not change your weekly mg, it changes how that mg is distributed across the week. Smaller, more frequent injections produce flatter blood levels.

Common UK Vials and Their Math

Sustanon 250 (250 mg/mL): The most commonly prescribed testosterone in UK NHS and private practice. 1 mL ampule contains 250 mg. For a 125 mg/week protocol injected twice weekly, that's 62.5 mg = 0.25 mL twice weekly.

Testosterone enanthate 250 mg/mL (Rotexmedica, etc.): Common in UK private TRT. Same volume math as Sustanon at the same concentration.

Testosterone cypionate 200 mg/mL: Available through some UK private clinics and European imports. For 140 mg/week, that's 0.7 mL once weekly or 0.35 mL twice weekly.

Calculator and Tracker

The TRT Dose Calculator runs all of these conversions automatically for any UK concentration, weekly dose, and frequency. The same numbers inside the Regimen app (iPhone and Android) get logged into your protocol with half-life modelling and lab tracking.

What to Bring to Your UK Private TRT Consultation

If you're heading to a first appointment with Optimale, Mansmatters, ConsultantCare, or another UK private TRT prescriber:

• Recent total testosterone, free testosterone, SHBG, and oestradiol labs (within the last 3 months ideally)
• HbA1c and fasting glucose
• Lipid panel
• Full blood count (especially haematocrit, since TRT raises it)
• Any previous TRT history (doses, esters, frequencies tried)
• Your symptom pattern (libido, energy, mood, body composition)

Bringing this in saves a consultation cycle and lets the prescriber design a dosing strategy at the first visit.

FAQ

How do I convert mg to mL for UK testosterone?

Divide the mg by the concentration (mg/mL) on the vial. Example: 100 mg ÷ 200 mg/mL = 0.5 mL. The TRT Dose Calculator does this automatically.

What does 0.5 mL of testosterone equal in mg?

At 200 mg/mL, 0.5 mL = 100 mg. At 250 mg/mL (Sustanon 250 or enanthate 250), 0.5 mL = 125 mg. At 100 mg/mL, 0.5 mL = 50 mg.

Is 1 mL of testosterone per week too much?

It depends on concentration. 1 mL at 100 mg/mL = 100 mg/week (standard TRT). 1 mL at Sustanon 250 = 250 mg/week (high-end optimised TRT, common in UK private prescribing). Discuss with your TRT prescriber whether the dose suits your labs.

How do I draw 0.25 mL on a 1 mL insulin syringe?

0.25 mL sits at the 25-unit mark on a standard 1 mL insulin syringe (marked 0 to 100 units). One-quarter of the way up the barrel.

Can I use an insulin syringe for TRT?

Yes, for daily microdosing and most subcutaneous protocols. UK private TRT clinics routinely prescribe insulin syringes (29G or 30G, 0.5 mL or 1 mL) for sub-Q daily or EOD injections. For intramuscular protocols, you'll need a longer needle (typically 23G to 25G, 1 to 1.5 inch).

Why is my TRT prescribed every 14 days on the NHS?

Historical NHS protocol for Sustanon 250 and testosterone enanthate is every 10 to 14 days. The pharmacokinetics produce significant peak/trough swings, which many patients tolerate poorly. UK private TRT clinics typically switch this to once or twice weekly for flatter blood levels without changing the weekly mg total.

This article is for educational purposes only and is not medical advice. Consult your prescribing clinician before changing your TRT protocol or injection schedule.