Ester Weight Calculator
Convert esterified testosterone mg into actual free testosterone — the ester is dead weight.
The mg number on the vial or in your protocol — e.g. 200 mg testosterone enanthate.
The most common long ester; ~72% free testosterone.
Free testosterone
Actual free testosterone
144.0 mg
200 mg enanthate × 72.0% = 144.0 mg free T · 56.0 mg ester weight
The math — free-T fraction by ester
| Ester | Formula | MW (g/mol) | Free T | Ester % |
|---|---|---|---|---|
| Suspension (no ester) | C19H28O2 | 288.42 | 100.0% | 0.0% |
| Propionate | C22H32O3 | 344.49 | 83.7% | 16.3% |
| Phenylpropionate | C28H36O3 | 420.58 | 68.6% | 31.4% |
| Isocaproate | C25H38O3 | 386.57 | 74.6% | 25.4% |
| Enanthate | C26H40O3 | 400.59 | 72.0% | 28.0% |
| Cypionate | C27H40O3 | 412.61 | 69.9% | 30.1% |
| Decanoate | C29H46O3 | 442.67 | 65.2% | 34.8% |
| Undecanoate | C30H48O3 | 456.70 | 63.2% | 36.8% |
Free-T fraction = 288.42 (testosterone MW) ÷ esterified MW. Molecular weights from PubChem / USP / EP reference-standard listings.
Educational use only — not medical advice. The ester itself has no hormonal activity; it is cleaved after injection, so only the free-testosterone fraction reaches the bloodstream as active hormone. Blend products (e.g. Sustanon) combine several esters — convert each one separately and add the free-T amounts.
About this tool
Injectable testosterone is always dosed as the esterified molecule, but the ester itself has no hormonal activity. It's a fatty-acid chain that slows release from the injection depot, and it's cleaved off in the bloodstream, leaving free testosterone as the only active hormone. That means the mg on the vial overstates the hormone content: 200 mg of testosterone enanthate delivers only ~144 mg of free testosterone. This calculator converts any esterified amount into actual free testosterone mg using the molar-mass ratio, with the molecular-weight math shown so you can verify every fraction.
How to use it
- 1 Select your testosterone ester — propionate, enanthate, cypionate, phenylpropionate, isocaproate, decanoate, undecanoate, or suspension (no ester).
- 2 Enter the esterified amount in mg — the number on the vial or in your protocol.
- 3 Read the free testosterone result: esterified mg multiplied by the ester's free-T fraction, plus how many mg are just ester weight.
- 4 For blends like Sustanon, convert each component separately and add the free-T amounts.
Frequently asked questions
Why does 250 mg of testosterone enanthate not equal 250 mg of testosterone?
The ester is part of the molecule's weight. Testosterone enanthate has a molecular weight of 400.59 g/mol versus 288.42 g/mol for free testosterone, so only about 72% of the labeled mass is active hormone — 250 mg enanthate delivers roughly 180 mg of free testosterone.
Which ester gives the most free testosterone per mg?
Shorter esters carry less dead weight: propionate is ~83.7% free testosterone, enanthate ~72.0%, cypionate ~69.9%, undecanoate ~63.2%. Suspension has no ester at all, so it's 100% active hormone by weight.
Does the ester change how strong the testosterone is?
No. Once cleaved, every ester releases the identical testosterone molecule. The ester only changes release speed (half-life) and the fraction of each injected mg that is actual hormone.
Educational use only — not medical advice. Results are estimates based on published formulas and models.