About the 2D:4D Test

The 2D:4D Test uses AI to measure your finger ratio and determine your hormone tendency type.

What is the 2D:4D Ratio?

The 2D:4D ratio is the ratio between the length of your index finger (2nd digit, 2D) and ring finger (4th digit, 4D). Research suggests this ratio is determined by the relative amounts of testosterone and estrogen exposure during fetal development in the womb.

Scientific Background

Since the initial study published in 1998, the relationship between the 2D:4D ratio and prenatal hormone exposure has attracted growing academic attention. Hundreds of follow-up studies have reported statistical correlations between this ratio and various traits including personality, athletic ability, and cognitive style. Key studies: • Manning et al. (1998) - Human Reproduction • Zheng & Cohn (2011) - PNAS • Hönekopp & Watson (2010) - Personality and Individual Differences

How We Measure

The 2D:4D Test uses Google's MediaPipe Hands AI model to precisely detect finger joint positions. Based on the 21 detected hand joint coordinates, we calculate the lengths of the index and ring fingers and derive their ratio. All processing happens in your browser — your photos are never sent to any server.

Classification Criteria

Different thresholds are applied by gender: Male (average 0.947) • Ratio < 0.95 → Testosterone-dominant (Testo Male) • Ratio ≥ 0.95 → Estrogen-dominant (Estro Male) Female (average 0.965) • Ratio < 0.97 → Testosterone-dominant (Testo Female) • Ratio ≥ 0.97 → Estrogen-dominant (Estro Female)

Important Notice

This test is a personality assessment inspired by academic research. It does not provide medical or psychological diagnosis. As it is based on statistical tendencies, it cannot definitively judge an individual's personality, ability, or health. If you suspect a hormone-related health issue, please consult a medical professional. Additionally, 2D:4D research is an ongoing field, and some claims have failed to replicate in follow-up studies (e.g., Hönekopp & Watson 2010, Voracek 2011). Treat the results of this service as a reference for academic curiosity, not as a diagnosis.

Editorial & Operations

This service is operated by an individual. The operator does not hold credentials in medicine or psychology, and the service does not provide medical or psychological assessment. Editorial principles: • All articles cite peer-reviewed journals and meta-analyses as primary sources • Topics with academic disagreement are presented alongside critical views, not just the dominant claim • Articles are updated when new meta-analyses or replication-failure reports are published • Wording that implies medical conclusions, diagnosis, or prescriptions is avoided Questions or factual corrections are accepted by email.

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