The only located Japanese study measured about 102 clinic patients at roughly 12.6 cm stretched. The claimed 13.5 cm erect matches no Japanese measurement anyone can point to, and one clinic sample of a hundred men is a thin basis for a country of 51 million adult men either way.
What the internet claims
13.5cm
labelled erect
The compilation behind the viral maps
D
vs
What was measured
12.60cm
stretched, 102 men
Kadono et al., 2017
The claim runs 0.90 cm above the measurement, and the two do not measure the same thing: the claim says erect, the study measured stretched. There is no accepted way to convert between them.
What was actually measured in Japan?
Kadono 2017 is what exists: around a hundred patients, clinician-measured, stretched. It is a perfectly reasonable clinical paper and an unreasonable foundation for a national average. A sample of 102 puts the uncertainty on the mean at roughly a third of a centimetre before you account for the sample being clinic-based rather than population-based.
Japan is a good example of a country where the absence of data is surprising. It has a large, wealthy research sector, a national health system, and a substantial urology literature. What it does not appear to have is a normative penile measurement study of the general adult population. Neither do Spain, Russia, Poland, Indonesia, Pakistan or the Philippines. The gaps in this map are not where you would guess.
The claimed figure of 13.5 cm is also worth reading against the pooled Asian estimate from Belladelli 2023, which is 11.74 cm erect with a confidence interval running from 10.18 to 13.29. The Japanese claim sits outside the top of that interval. That does not make it wrong. It does mean nothing in the pooled regional literature supports it.
How does that compare with the rest of the world?
The claim puts Japan 89th of 119 countries on the ranked list. Here is that number set against the figures that come with a method attached.
Figure
cm
What it is
The claim for Japan
13.50
Labelled erect. No method, no sample size, no reference.
Kadono et al.
12.60
stretched, 102 men, 2017. The best located
measurement in Japan.
Clinically measured worldwide
13.12
Erect, 15,521 men. Veale 2015, the pooled clinical figure.
Pooled worldwide
13.93
Erect, 55,761 men. Belladelli 2023, 75 studies.
Pooled for Asia
11.74
Erect, 95 % confidence interval
10.18–13.29 cm
. Belladelli 2023.
That last interval is 3.11 cm wide,
for a whole continent, from the largest meta-analysis there is. The claimed map it sits
under spreads all 119 countries across
7.9 cm and prints every
country to one decimal place. Read those two sentences together and you have the
entire problem with penis size by country.
How many men does the claim cover?
102 measured → 51,000,000 described
102 men in Japan appear in the studies this register could locate. The claimed figure is applied to roughly 51,000,000 adult men: one measured man for every 500,000.
Where would you land in Japan?
Against the claimed figure, because that is the number people mean when they ask. It
is the weaker of the two numbers above, and the calculator says so. Everything is
computed in your browser and nothing you enter is stored or sent anywhere.
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1,350,250,000men smaller
1,350,240,000men larger
50 of 100 men worldwide are larger than you.
L 13.6 cm
Estimated from the claimed world mean of 13.6 cm across ≈ 2,700,490,000 adult
men in 119 countries. You beat the claimed mean in 31 of them. The
claims are the internet's, not ours; we are grading them one by one.
See the audit.
What should you take from this?
Japan's number is a claim, not a measurement, and the one Japanese study on record points lower and measures something else. Anyone using the ranking to say something about Japanese men is using a figure with no author.
The same applies to the country's position relative to its neighbours. Japan, South Korea and Taiwan occupy three adjacent slots near the bottom of the map on the strength of 123 conscripts, about a hundred clinic patients, and a 40-man study from 1992.
Nearby in the register
The nearest countries with an entry of their own here.
Nearer still, and with nothing to show: North Korea, Philippines, Mongolia. Those
countries carry a claimed figure on every map and no located study behind it, so they
have no page here. The method page lists all of them.
Sources for this page
Kadono et al., 2017, n = 102. Clinician-measured, stretched; clinic patients.
Veale D et al. Am I normal? BJU International 2015; 115(6): 978–986. The pooled
clinical figures used throughout this site.
Belladelli F et al. Worldwide Temporal Trends in Penile Length. World J Mens Health
2023; 41(4). The regional pooled figures and confidence intervals.
The full reference list, the grading scheme and all 119 claims are on the
method and sources page.