What you’re about to read may seem so strange and uncanny as to warrant derision as pseudoscience. But hang in there. Because it’s not. Study after study has shown it to be a scientific reality, one that offers fascinating insights into human biology and psychology.
The uncanny phenomenon is this: the ratio of your second (i.e., index finger) to fourth (i.e., ring finger) finger is a reliable indicator of your prenatal testosterone exposure during gestational weeks 12-16.
So what? Why should we care about prenatal testosterone?
The short answer is that our degree of testosterone exposure, as approximated by our digit ratio, corresponds to how masculine versus feminine our brain and cognition is. In particular, as we will soon discuss, Myers-Briggs enthusiasts may be excited to learn that your digit ratio likely corresponds to your Thinking (T) – Feeling (F) preference, with more masculine ratios suggesting a Thinking preference and more feminine ratios a Feeling preference. Before discussing digit ratio and its relationship to personality type, however, let’s first examine some of the key scientific findings and effects of prenatal testosterone.
Finger / Digit Ratio & Testosterone Research
Human and animal studies have consistently demonstrated that prenatal testosterone exposure steers gender-related behavior and brain development. According to this paper in the Journal of Research in Personality, animal research suggests that “the effects of prenatal testosterone are graded and linear—higher levels of exposure lead to more male-typical behavior and brain structure.” In other words, higher prenatal testosterone paves the way for a more masculine brain.
Before proceeding any further, it’s important that we distinguish between prenatal versus circulating testosterone (i.e., the amount currently in your bloodstream). While the scientific jury is still out, prenatal and circulating testosterone levels may be relatively unrelated. HOWEVER, we also know that prenatal testosterone exposure increases sensitivity to testosterone throughout life. So if you were exposed to higher levels of testosterone prenatally, your system will show a heightened response to whatever testosterone is in your bloodstream compared to individuals with lower prenatal exposure. Thus, those with masculinized brains don’t require high levels of circulating testosterone to experience its effects.
Another interesting finding is that children tend to have digit ratios similar to their mother’s. This suggests that a mother’s degree of masculinity / femininity will be reflected in her offspring (so be sure to call your mom today and thank her for her contributions to your brain and psychology).
For those who aren’t mathematically inclined, digit ratio can be a bit confusing because:
Lower Digit Ratio = Higher Prenatal Testosterone
Technically speaking, they are inversely related. Men generally have lower digit ratios and higher prenatal testosterone than women. To minimize any confusion regarding this inverse relationship, I will typically describe the ratios as more masculine (i.e., “masculine ratio”) or feminine rather than using the lower vs. higher terminology.
Prenatal testosterone exposure and digit ratio are also related to sexual orientation. In particular, lesbians tend to have a more masculine digit ratio than heterosexual women. The findings are somewhat less clear in gay men. However, according to the leading expert in this field, John Manning, white homosexual men generally have more feminine finger ratios.
Wikipedia has an extensive list of traits associated with digit ratio. Here are some of the more noteworthy correlations:
- Perceived ‘dominance’ and ‘masculinity’ of man’s face (i.e., broader face)
- Tendency toward non-monogamy
- Poorer empathic-accuracy performance
- Higher rates of ADHD and autistic traits
- Higher rates of alcohol dependence in men
- Increased incidence of left-handedness
- Higher numeracy (compared to literacy) in children
- Increased risk of anxiety / depression in males
- Tendency toward monogamy
- Lower risk of alcohol dependency
- Reduced performance in sports
- Higher in Big Five Openness, as well as paranormal / superstitious beliefs
- Higher verbal fluency (both sexes) and visual recall in females
- Higher literacy (compared to numeracy) in children
How to Measure Your Fingers
Straighten your fingers and look at the palm of your hand. We are concerned with the second (index finger) and fourth (ring finger) fingers. At the base of your index and ring fingers (where they meet the palm) there are creases. Choose a midway point on the crease and mark it with a pen if you wish. Measure from there to the tip of the finger, using a caliper, ruler or tape measure, being as precise as possible. See the image below.
Calculating Your Digit Length Ratio
To calculate your digit ratio, simply divide the length of your index finger (“2D”) by that of your ring finger (“4D”) as follows:
Index Finger Length / Ring Finger Length = Digit Ratio
Or, to express the same thing using different terminology:
2D / 4D = Digit Ratio
Interpreting Your Digit Ratio
We will now interpret your digit ratio using normative data from two empirical studies: one from the University of Alberta and the other from Warwick University. For the sake of simplicity, I averaged the mean digit ratios and standard deviations from these studies. Please note the while the data from these studies appears to be reliable, other studies have reported ratios up to 0.01 higher (thus, a mean digit ratio of 0.96 rather than 0.95 in males).
Since the data is organized by sex, it’s important to keep in mind that the mean digit ratio for males (0.95) is significantly more masculine than the mean ratio for females (0.97). Moreover, for what it’s worth, Manning typically uses 0.92 to represent a characteristically low (i.e., highly masculine) ratio. As illustrated below, this ratio is one standard deviation below the mean for males.
Here’s the digit ratio distribution for the male participants:
And here’s the digit ratio distribution for female participants:
Digit Ratio & Myers-Briggs Personality Type
While there’ve been a couple studies comparing digit length with the Big Five taxonomy, to my knowledge, none have done so with the Myers-Briggs. So just for fun, I decided to make some ballpark predictions regarding the probable digit ratios of Myers-Briggs Thinkers (T) versus Feelers (F).
Both research and ordinary experience suggests a significantly higher percentage of Thinking (i.e., more masculine brain) males and Feeling (i.e., more feminine brain) females. Assuming that roughly two-thirds of men are Thinkers and females Feelers, we can use the above diagrams to make the following estimates:
Thinkers (T): 0.97 and lower
Feelers (F): Greater than 0.97
Thinkers (T): Less than 0.95
Feelers (F): 0.95 and higher
Again, these predictions are provisional and certainly won’t hold true for everyone. Nonetheless, there’s good reason to believe that digit ratio will correlate with T-F preference, even if only moderately.
Learn More in Our Books:
My True Type: Clarifying Your Personality Type, Preferences & Functions
The 16 Personality Types: Profiles, Theory & Type Development
Masculine & Feminine in the Myers-Briggs vs. Big Five
Face Thyself: How Your Body Reveals Your Personality Type
Cognitive Styles of Thinkers (T) vs. Feelers (F): Visual, Spatial & Verbal
Lady INTJ says
Very interesting. For what it’s worth: INTJ woman (with INTJ mother), <0.92 ratio
A.J. Drenth says
Thanks Lady INTJ for chiming in!
Female INTJ, ratio 1.05 here :)
A.J. Drenth says
Thanks Tereza for taking part in our little experiment and sharing your results:)
Very interesting! Got 1.09, so according to this, the “feeler” is off the charts with this one.
A.J. Drenth says
Thanks Lisa for sharing your results.
INTP male here: 0.94.
This prediction holds for me, at least. I’m a female INTP and I measured my digit ratio at about 94.5, so “T” but close to borderline on the predicted T/F threshold for females. It often feels like I straddle that T/F threshold, which almost prevented me from finding my true type when I first learned about the Myers-Briggs in my 20s. Initially, I mistyped myself as an INFP. In that type, I found many things that really resonated with my personality, and still do… and I just shrugged my shoulders at the parts that were glaringly wrong. It wasn’t until a few years later that I retook the test and identified my unmistakable INTP-ness. Now in my 30s, after reading a huge amount of your literature on INTPs (including both books), there is simply no question. Those books feel uncannily written about me and my life’s path. It was almost at the level of an awakening.
And yet–I still feel like I bring an “F” flavor to the INTP type. If I recall correctly, even my more recent Myers-Briggs results only showed a narrow lead for T. I assume this is at least partly due to the fact that as a female, I’ve been somewhat groomed to Feeling behaviors and abilities, and so they don’t feel as foreign to me as they might to my male INTP counterparts. It’s now interesting to consider that there might also be a more biologically-based reason to describe my position on the T-F spectrum, perhaps hinted at by the digit ratio. It would be interesting to hear the experiences of a male INTP who is also borderline on that digit ratio.
Despite being an INTP I’ve always been good at empathizing, though as I’ve gotten older I most often avoid situations that might induce empathy because of the energy/emotion/time drain I know I’ll experience. The same thing goes for nurturing. I feel a strong drive to nurture, so I protect my time and energy by choosing nurturing situations carefully. One way to describe it is that I’ve got a pull towards F but T often overrides it, or at least tempers it.
It’s true that at times it feels like my T & F inclinations are engaged in a battle with each other (especially in my younger years), but when I’m operating at my best it feels like they’re working hand-in-hand, taking the lead when appropriate, and allowing me to navigate the world with greater ability.
A.J. Drenth says
Thanks so much Claire for sharing your ratio and how it might connect with your T-F preference.
Michael Wickham says
Thanks, guys (all genders, of course). I’m a 1.72 male INTP (as so I continually test out). Now I feel verifiably weirder than ever (ha, ha).
A.J. Drenth says
Thanks so much Michael. Your ratio does seem quite high. You may want to double check your measurement and ensure that you used 2D/4D and not vice-versa.
I’m a female INFJ with more than a few “thinker” characteristics — 0.95 ratio
I remember hearing about this in a class and, without having to measure, it’s quite evident. Spot on for this female T.
this is a tricky one, but so is my personality:
right hand ratio: 0.97
left hand ratio: 0.91
I measured it all 5 times over, really, and I’m rather accurate at measuring.
A.J. Drenth says
Interesting. In Manning’s 2007 book, “The Finger Book,” he contends that the left hand is more indicative for females and the right for males. I’m not sure if this still holds true or not. More recent studies have used either the right hand only or both hands.
Male INFP, ratio 1.01. Quite interesting. Thank you for sharing.
A.J. Drenth says
You’re welcome Paul. Thanks too you as well.
Female ENTP (with an INFP mother), 0.97 ratio!
Dawn Upham says
Female INFP: Ratio is .985
Infp 0.96 ratio 😉
Oh this was so interesting. I got my whole family to participate this morning. First I measured everyone’s hands and did the calculations, and then I got my husband and sons (18 & 14 yrs ) to take the Personality Junkie online test as a “late Valentines day gift ” for me.
Myself = female INFP, ratio 1.04
Husband= male ESTJ, ratio .96
18 yr old son= male INTP, ratio .98
14 yr old son= male (he tested INTJ), ratio .96
My 14 yr old really struggled with the personality test and I don’t put to much validity in his results. He had left about half the answers blank and didn’t know how he felt about them, thinking maybe he would respond one way in one circumstance and another way in another. When I looked at the questions he was struggling with I could usually see him in both answers, so I understood why he was having difficulty. He is an adolescent and I think it’s a pretty turbulent stage for identity. As a little kid I guessed him as an ISTJ or possibly ISFJ, but I’m really not sure anymore.
As for the 18 yr old, he had done the 16 personalities test in a high school class and got INFP, and he related to a number of things about it saying that his F had scored 51% and T 49% at the time, but I think the whole INTP has always fit him so much better as a whole. But I guess you never know.
Trait wise my husband and I have lots of opposites ones to each other, and I can see a real mix of them in my boys. I was curious if my children would indeed have digit ratios similar to mine, but it looks like they are closer to their dads. I wonder if this is different for mother and daughters as opposed to mother and sons?
INFJ 0.90 so that is very masculine for a feeler if this theory holds. I am heterosexual but do have some sensitivity issues with testosterone that have had some health impacts. Converse to the theory presented in this article – my personality is typically much more ‘feminine’ so it doesnt hold for me.
Right handed INFP with 1.02 ratio in both hands.
Background: 100% lesbian and tomboy entire life. Always very athletic with a stout, muscular build. And my current job is a bicycle technician.
I’m described by friends as “intellectual,” have always been very logical, was in advanced academic classes in middle school, graduated HS early and was Magna Cum Laude in College.
However, I’ve been writing poetry since elementary school, hug trees every chance I get, and turn any show or movie off as soon as it starts getting sad or stressful because my empathy knows no bounds.
Never had any substance abuse problems but I do struggle with monogamy and have no desire to be a parent.
Perhaps I’m just well-rounded? If so, I give credit to my ISTJ mom.
I am a am a male INTP and have a 1.05 ratio. But in all fairness, I’ve always felt my feminine and masculine is pretty balanced…
Thank you, this is really interesting, but I’m confused: It’s 1,03 for my right hand and 0,94 for my left hand. I’m female, left-handed and still not sure whether I’m an INTP with high Fe or an INFJ with high Ti. Is the dominant hand perhaps more important? Also, left-handedness is more commonly found in people with a low digit ratio… What do you think?
A.J. Drenth says
Hi Eva, As I said in the previous comment, in Manning’s 2007 book, “The Finger Book,” he contends that the left hand is more indicative for females and the right for males. I’m not sure if this still holds true or not. More recent studies have used either the right hand only or both hands. I definitely wouldn’t base your type on this alone. It’s more like a small piece of the puzzle.
I think the mean digit ratio values stated in the above estimates for thinking/feeling males/females have got reversed.
Shouldn’t it be Male Thinkers 0.95 and lower n Female Thinkers 0.97 and lower and likewise for Male and Female Feelers?
A.J. Drenth says
Good question. I set the values based on two assumptions: 1) that the graphs were normal distributions for males and females; 2) that roughly two-thirds of males are thinkers and one-third of females are thinkers. Thus, I set the male ratio cutoff at .97 (roughly 66th percentile on their graph) and females at .95 (roughly 33rd percentile on their graph). Hope that makes sense.