Free concentration tool
Topical Finasteride Concentration Calculator
Convert finasteride mass and vehicle volume into a percentage and mg/mL, work out what one application delivers, and see how long a bottle lasts.
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- Alpha Health Finder Editorial Team
- Last reviewed
What the percentage on a compounded bottle actually means
Start with the part nobody selling this will lead with: there is no FDA-approved topical finasteride product in the United States. Every finasteride product listed in Drugs@FDA is an oral tablet — PROPECIA at 1 mg for male pattern hair loss and PROSCAR at 5 mg for benign prostatic hyperplasia. A topical solution is therefore compounded or imported, and the FDA is explicit that compounded drugs are not FDA-approved: they are not reviewed for safety, effectiveness or manufacturing quality before dispensing. There is no label to quote. There is no authoritative concentration, no authoritative application volume and no authoritative frequency for a topical. Whatever your prescriber specified is the only figure that applies to your bottle, and this page checks that figure rather than proposing one.
The convention the arithmetic turns on is percent weight-per-volume. One percent w/v means one gram of drug in 100 mL of finished solution: 1000 mg ÷ 100 mL = 10 mg/mL. So 0.1% is 1 mg/mL, 0.25% is 2.5 mg/mL, and 0.0125% is 0.125 mg/mL. The mistake is dividing by a hundred instead of multiplying by ten — reading 0.1% as 0.1 mg/mL, which is out by a factor of ten in the direction that matters.
One caveat a conversion factor cannot carry. A percentage can also be quoted as w/w — grams per 100 grams — and the alcohol-based vehicles these solutions use are appreciably lighter than water, so the two are not interchangeable. The 0.25% solution used in the published dose-ranging work delivered 2.275 mg per mL, not the 2.5 mg/mL that straight w/v gives. Everything on this page is w/v. If the paperwork with your bottle says w/w, the figures here are about 9% high for that formulation and the compounding record is the number to trust.
After that, it is one division and its rearrangements. Concentration is finasteride mass divided by finished volume; the mass a volume needs is that volume times the target concentration; the volume a mass must occupy is that mass divided by the target. What one application delivers is concentration times the volume applied, and how long the bottle lasts is its volume divided by that application, divided again by applications per day.
The figure this tool deliberately will not produce is an oral-equivalent dose. Milligrams applied to a scalp and milligrams swallowed are not the same exposure, and the gap is large in both directions. In the phase III trial of a topical finasteride spray, maximum plasma finasteride concentrations were more than 100 times lower than with the oral tablet, and the reduction in mean serum DHT was 34.5% against 55.6% for oral — while hair count gains were numerically similar. Lower systemic exposure is the entire point of the route; it is not zero, and it is not proportional to the milligram figure on the bottle.
A note on what is absent here on purpose: there is no vehicle, no solvent, no method and no supplier anywhere on this page. This is a calculator for a preparation a prescriber has already specified, in the same way a units converter is a calculator for a dose someone else wrote. Preparing a drug is compounding, it is regulated, and it is not a home exercise.
The formula
concentration (mg/mL) = finasteride (mg) ÷ finished volume (mL)
concentration (% w/v) = concentration (mg/mL) ÷ 10
finasteride (mg) = finished volume (mL) × target (mg/mL)
finished volume (mL) = finasteride (mg) ÷ target (mg/mL)
mg per application = concentration (mg/mL) × application (mL)
applications per bottle = finished volume (mL) ÷ application (mL)
days per bottle = applications per bottle ÷ applications per day
1% w/v is 1 g in 100 mL, which is 10 mg/mL — the factor of ten that turns a percentage into a concentration. The solid’s own displaced volume is ignored, as it is below the graduation of any bottle holding these masses. Part applications are not counted, because a remainder in the bottle is solution but not another dose.
Worked example
60 mg of finasteride in a finished volume of 60 mL, 1 mL applied once daily:
- Concentration = 60 mg ÷ 60 mL = 1 mg/mL
- As a percentage = 1 ÷ 10 = 0.1% w/v
- One application = 1 mg/mL × 1 mL = 1 mg of finasteride
- At 1 application a day that is 1 mg applied per day
- The bottle holds 60 mL ÷ 1 mL = 60 applications
- Which lasts 60 days at that frequency
- That 1 mg on the scalp is the same number as the 1 mg oral tablet and not the same exposure — nothing here converts between the two
Topical finasteride dilution chart — concentration by mass and volume
Resulting strength as percent w/v. Read down for the milligrams of finasteride, across for the finished volume of the solution.
| Finasteride | 30 mL | 50 mL | 60 mL | 100 mL |
|---|---|---|---|---|
| 15 mg | 0.05%0.5 mg/mL | 0.03%0.3 mg/mL | 0.025%0.25 mg/mL | 0.015%0.15 mg/mL |
| 30 mg | 0.1%1 mg/mL | 0.06%0.6 mg/mL | 0.05%0.5 mg/mL | 0.03%0.3 mg/mL |
| 60 mg | 0.2%2 mg/mL | 0.12%1.2 mg/mL | 0.1%1 mg/mL | 0.06%0.6 mg/mL |
| 90 mg | 0.3%3 mg/mL | 0.18%1.8 mg/mL | 0.15%1.5 mg/mL | 0.09%0.9 mg/mL |
| 120 mg | 0.4%4 mg/mL | 0.24%2.4 mg/mL | 0.2%2 mg/mL | 0.12%1.2 mg/mL |
| 150 mg | 0.5%5 mg/mL | 0.3%3 mg/mL | 0.25%2.5 mg/mL | 0.15%1.5 mg/mL |
Percent here is weight-per-volume throughout: 1% w/v is 10 mg/mL. Every cell is computed by the same function the calculator above uses, so the two cannot disagree.
Milligrams of finasteride per application
What one application delivers. Read down for the strength on the bottle, across for the volume you apply.
| Strength | 0.2 mL (200 µL) | 0.5 mL (500 µL) | 1 mL | 2 mL |
|---|---|---|---|---|
| 0.0125%0.125 mg/mL | 0.025 mg0.05 mg/day twice daily | 0.0625 mg0.125 mg/day twice daily | 0.125 mg0.25 mg/day twice daily | 0.25 mg0.5 mg/day twice daily |
| 0.025%0.25 mg/mL | 0.05 mg0.1 mg/day twice daily | 0.125 mg0.25 mg/day twice daily | 0.25 mg0.5 mg/day twice daily | 0.5 mg1 mg/day twice daily |
| 0.05%0.5 mg/mL | 0.1 mg0.2 mg/day twice daily | 0.25 mg0.5 mg/day twice daily | 0.5 mg1 mg/day twice daily | 1 mg2 mg/day twice daily |
| 0.1%1 mg/mL | 0.2 mg0.4 mg/day twice daily | 0.5 mg1 mg/day twice daily | 1 mg2 mg/day twice daily | 2 mg4 mg/day twice daily |
| 0.25%2.5 mg/mL | 0.5 mg1 mg/day twice daily | 1.25 mg2.5 mg/day twice daily | 2.5 mg5 mg/day twice daily | 5 mg10 mg/day twice daily |
| 0.3%3 mg/mL | 0.6 mg1.2 mg/day twice daily | 1.5 mg3 mg/day twice daily | 3 mg6 mg/day twice daily | 6 mg12 mg/day twice daily |
| 0.5%5 mg/mL | 1 mg2 mg/day twice daily | 2.5 mg5 mg/day twice daily | 5 mg10 mg/day twice daily | 10 mg20 mg/day twice daily |
The lower line is the daily total if that application is repeated twice a day. These are milligrams placed on the scalp, not an oral-equivalent dose: the approved oral dose for androgenetic alopecia is 1 mg once daily by mouth, and no published figure converts one route into the other.
Finasteride needed for a target strength
Milligrams of finasteride the finished volume in the column heading must contain to reach the strength in the row.
| Target strength | 30 mL | 50 mL | 60 mL | 100 mL |
|---|---|---|---|---|
| 0.0125%0.125 mg/mL | 3.75 mg | 6.25 mg | 7.5 mg | 12.5 mg |
| 0.025%0.25 mg/mL | 7.5 mg | 12.5 mg | 15 mg | 25 mg |
| 0.05%0.5 mg/mL | 15 mg | 25 mg | 30 mg | 50 mg |
| 0.1%1 mg/mL | 30 mg | 50 mg | 60 mg | 100 mg |
| 0.25%2.5 mg/mL | 75 mg | 125 mg | 150 mg | 250 mg |
| 0.3%3 mg/mL | 90 mg | 150 mg | 180 mg | 300 mg |
| 0.5%5 mg/mL | 150 mg | 250 mg | 300 mg | 500 mg |
A figure for checking a compounding record against the strength printed on the bottle. It is not a method: preparing the solution is compounding, which is regulated and belongs to a pharmacy.
How long a bottle lasts
Whole days of supply. Read down for the bottle size, across for how much you apply and how often.
| Bottle | 0.5 mL once daily | 1 mL once daily | 1 mL twice daily | 2 mL once daily |
|---|---|---|---|---|
| 15 mL | 30 days30 applications | 15 days15 applications | 7 days15 applications | 7 days7 applications |
| 30 mL | 60 days60 applications | 30 days30 applications | 15 days30 applications | 15 days15 applications |
| 50 mL | 100 days100 applications | 50 days50 applications | 25 days50 applications | 25 days25 applications |
| 60 mL | 120 days120 applications | 60 days60 applications | 30 days60 applications | 30 days30 applications |
| 100 mL | 200 days200 applications | 100 days100 applications | 50 days100 applications | 50 days50 applications |
| 120 mL | 240 days240 applications | 120 days120 applications | 60 days120 applications | 60 days60 applications |
Part applications and part days are not counted. This is the volume arithmetic only — the beyond-use date of a compounded solution is set by the pharmacy that made it and is frequently shorter than the bottle would otherwise last.
Frequently asked questions
- Is topical finasteride FDA-approved?
- No. There is no FDA-approved topical finasteride product in the United States. Every finasteride product in Drugs@FDA is an oral tablet: PROPECIA at 1 mg, indicated for the treatment of male pattern hair loss in men only, and PROSCAR at 5 mg for benign prostatic hyperplasia. Any topical is compounded or imported, and the FDA states plainly that compounded drugs are not FDA-approved and are not reviewed for safety, effectiveness or manufacturing quality before they are dispensed. One caveat worth knowing, because it looks like a contradiction: openFDA — the label-listing database, which is not the approvals database — does now return a topical finasteride foam, self-registered under marketing category "OTC Monograph Drug". Finasteride is prescription-only and appears in no OTC monograph, so that category cannot be correct, and a listing in openFDA is a filing by a labeler rather than a decision by the FDA. Drugs@FDA, which records approvals, still contains no topical finasteride application. That is why this page quotes the oral label for what is documented and does not pretend a topical label exists.
- How do I convert a finasteride percentage into mg/mL?
- Multiply by ten. Percent on a solution means weight-per-volume, so 1% w/v is one gram in 100 mL, which is 1000 mg ÷ 100 mL = 10 mg/mL. That makes 0.1% equal to 1 mg/mL, 0.25% equal to 2.5 mg/mL, 0.05% equal to 0.5 mg/mL and 0.0125% equal to 0.125 mg/mL. The common error is dividing by a hundred and reading 0.1% as 0.1 mg/mL, which is ten times too low. Going the other way, divide mg/mL by ten to get the percentage.
- How much finasteride is in one application of a 0.1% solution?
- 0.1% is 1 mg/mL, so a 1 mL application carries 1 mg, a 0.5 mL application carries 0.5 mg and a 200 µL application carries 0.2 mg. At 0.25% — 2.5 mg/mL by weight-per-volume — the same three applications carry 2.5 mg, 1.25 mg and 0.5 mg. Multiply the concentration in mg/mL by the volume applied in mL; that is the whole calculation, and the chart above prints it for every combination.
- Why does the pregnancy warning matter for a topical finasteride solution?
- Because a solution is the exposure the oral label already warns about, in a form that spreads. The FDA label for PROPECIA states that finasteride "is contraindicated in women when they are or may potentially be pregnant" and that "women should not handle crushed or broken PROPECIA tablets when they are pregnant or may potentially be pregnant because of the possibility of absorption of finasteride and the subsequent potential risk to a male fetus." The label adds that intact tablets are coated and prevent skin contact "provided that the tablets have not been broken or crushed" — protection a liquid does not have. The label's own instruction if contact occurs is that "the contact area should be washed immediately with soap and water." A topical preparation, a wet scalp, a pillow and shared towels are exactly the crushed-tablet scenario the warning describes, and it applies to anyone in the household who is or may become pregnant.
- Does topical finasteride still get into the bloodstream?
- Yes, less than oral, but measurably. In the 24-week phase III trial of a topical finasteride spray, maximum plasma finasteride concentrations were more than 100 times lower than with the 1 mg oral tablet, and the reduction from baseline in mean serum DHT was 34.5% with topical against 55.6% with oral, while the hair count gain was numerically similar. An earlier dose-ranging study of a 0.25% solution found serum DHT fell 24–26% at 100–200 µL per day but 60–70% at 1 mL per day. Systemic exposure scales with how much you put on, and "topical" does not mean "local only".
- What concentration is topical finasteride usually made at?
- There is no standard, because there is no approved product to standardise against. The published clinical work clusters on a 0.25% solution: the phase III spray trial and the earlier dose-ranging study both used it, at 100 µL to 1 mL per day, which is 0.2275 mg to 2.275 mg of finasteride daily as that particular formulation was made. Compounded bottles are prepared to whatever a prescription specifies and strengths from roughly 0.0125% to 0.3% turn up. The strength on your bottle is a decision your prescriber made, not a figure this calculator or any other should suggest.
- How long does a bottle of topical finasteride last?
- Divide the bottle volume by the volume of one application, then by applications per day. A 60 mL bottle at 1 mL once daily is 60 applications and 60 days; the same bottle at 1 mL twice daily is 30 days. A 30 mL bottle at 0.5 mL twice daily is 60 applications and 30 days, and at 200 µL once daily it is 150 applications and 150 days. Whichever figure you get, the pharmacy's beyond-use date overrides it — a compounded solution frequently expires before the bottle empties.
- Can I work out an oral-equivalent dose from the milligrams I apply?
- No, and this tool will not try. A 1 mL application of a 0.1% solution is 1 mg of finasteride, the same number as the approved 1 mg oral tablet, and it is not the same exposure in either direction. Plasma concentrations in the phase III topical trial were over 100 times lower than oral while serum DHT still fell 34.5%, so the relationship is neither one-to-one nor a fixed fraction. The honest answer is that no labelled conversion exists, and the figures this page produces are milligrams in a bottle and milligrams on a scalp — nothing more.
Sources
- [1]PROPECIA (finasteride) tablets, 1 mg — FDA prescribing information (Organon LLC), DailyMed. Indicated for male pattern hair loss in MEN ONLY; recommended dose one tablet (1 mg) once daily; "PROPECIA is contraindicated for use in women who are or may become pregnant"; "Women should not handle crushed or broken PROPECIA tablets when they are pregnant or may potentially be pregnant"; if contact occurs "the contact area should be washed immediately with soap and water"
- [2]PROSCAR (finasteride) tablets, 5 mg — FDA prescribing information (Organon LLC), DailyMed. The other approved finasteride strength, indicated for benign prostatic hyperplasia rather than hair loss, carrying the same pregnancy contraindication and crushed-tablet handling warning
- [3]Drugs@FDA: FDA-Approved Drugs — searchable record of every approved application. Every approved finasteride product is an oral tablet; no topical finasteride dosage form is approved in the United States
- [4]U.S. Food and Drug Administration. Compounding and the FDA: Questions and Answers — "compounded drugs are not FDA-approved", meaning FDA does not verify their safety, effectiveness or quality before they are marketed
- [5]Piraccini BM, Blume-Peytavi U, Scarci F, et al. Efficacy and safety of topical finasteride spray solution for male androgenetic alopecia: a phase III, randomized, controlled clinical trial. J Eur Acad Dermatol Venereol. 2022;36(2):286–294. Maximum plasma finasteride concentrations >100 times lower and serum DHT reduction 34.5% vs 55.6% for topical vs oral
- [6]Caserini M, Radicioni M, Leuratti C, et al. Effects of a novel finasteride 0.25% topical solution on scalp and serum dihydrotestosterone in healthy men with androgenetic alopecia. Int J Clin Pharmacol Ther. 2016;54(1):19–27. 1 mL of the 0.25% solution stated as 2.275 mg finasteride; serum DHT −24/−26% at 100–200 µL/day versus −60/−70% at 1 mL/day
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Educational reference, not medical advice. Concentration arithmetic, not a prescription and not a formula. There is no FDA-approved topical finasteride in the United States; the strength, the volume and the frequency belong to your prescriber and to the pharmacy that compounded the preparation. Finasteride is contraindicated in women who are or may become pregnant, and the oral label warns against handling the drug in any uncoated form because of the risk to a male fetus — a liquid on skin, bedding or towels is exactly that exposure.