Why a dose in milligrams is not a volume in millilitres
Prescriptions are written in milligrams of testosterone. Vials and ampoules are labelled in milligrams per millilitre. The volume you draw up depends on both, which is where most confusion starts. 100 mg is 0.4 ml from a 250 mg/ml ampoule, 0.5 ml from a 200 mg/ml vial and a full 1 ml from a 100 mg/ml vial. Same dose, three different volumes.
Insulin syringes add a second layer. They are marked in units, not millilitres, and a standard U-100 syringe has 100 units per ml. So 0.4 ml is 40 units, and a 0.5 ml syringe tops out at 50 units. If a clinic tells you to inject "20 units" of a 200 mg/ml cypionate, that is 0.2 ml, or 40 mg.
The concentrations you will see on UK prescriptions
| Preparation | Concentration | Notes |
|---|---|---|
| Testosterone enantate (1 ml ampoule) | 250 mg/ml | Licensed in the UK. Usually split into weekly or twice-weekly doses in private practice. |
| Sustanon 250 (1 ml ampoule) | 250 mg/ml | A blend of four esters totalling 250 mg. Licensed in the UK; dosed by total ester weight. |
| Testosterone cypionate (multi-dose vial) | 200 mg/ml | Not licensed in the UK but widely prescribed privately as an import. The usual choice for subcutaneous dosing. |
| Nebido (testosterone undecanoate, 4 ml) | 250 mg/ml, 1,000 mg per dose | Long-acting. Given in clinic every 10 to 14 weeks; not self-injected. |
Our post on testosterone enantate, cypionate and Sustanon explains why the ester matters and why your prescriber chooses one over another.
Is 1 ml of testosterone a week enough?
It is the wrong question, because 1 ml is not a dose. From a 250 mg/ml ampoule, 1 ml a week is 250 mg a week, which is at or above the top of what UK clinics typically prescribe. From a 100 mg/ml vial it is 100 mg, which is at the lower end. The only sensible way to talk about a dose is in milligrams, and the only sensible way to decide whether it is enough is a blood test taken at the right point in the cycle.
For context, UK private practice commonly uses somewhere in the region of 100 to 200 mg of enantate or cypionate a week, split into two or more injections so levels stay steadier, and adjusts from there against trough bloods, haematocrit and symptoms. Where a man lands in that range, or outside it, is a decision for his prescriber. Men who feel the dose is wrong should ask for bloods and a review, not change the volume themselves.
Needles and syringes: what the numbers on the pack mean
Gauge (G) is the needle's width, and a higher number means a thinner needle. Length is given in millimetres or inches. Testosterone in oil is thick, so most people draw up with a wider needle and inject with a finer one.
| Use | Gauge | Length |
|---|---|---|
| Drawing up from a vial | 18G to 21G | 25 to 40 mm (1 to 1.5 in) |
| Intramuscular, thigh or glute | 23G to 25G | 25 to 38 mm (1 to 1.5 in), shorter for leaner men |
| Subcutaneous, abdomen or flank | 27G to 31G insulin needle | 6 to 13 mm (¼ to ½ in) |
Which route you use, and where, is covered in where to inject testosterone. Whatever you are prescribed, technique should be taught before you inject alone, and sharps go in a proper disposal bin.
What changes a dose, and what should not
Doses move for clinical reasons: a trough testosterone that is lower or higher than intended, a rising haematocrit, oestradiol symptoms, or a change in injection frequency. They should not move because of how you feel on one particular day, because of a forum thread, or because a vial is nearly empty. If something feels off, the next step is a blood test and a conversation, and at Arc every result is read by a doctor with a same-day call for anything seriously abnormal.
Not sure whether your levels justify treatment in the first place? Start with what testosterone levels qualify for TRT and the full guide to how to get TRT in the UK.
