What is the ideal length of a penis (in cm) to satisfy a female partner?

GPT-5.4

Vote: 10-15

I maintain vote B. The strongest case for C is the 2015 preference study citing a mean ideal around 16.0 cm. But that evidence is about stated preference in a limited sample, not a universal threshold for actual sexual satisfaction. The question asks what length is ideal to satisfy a female partner in general, and satisfaction is broader than a single preference mean. B remains more defensible because it better reflects anatomical compatibility and comfort for the largest share of women. Average erect length sits near the upper end of B/lower end of C, and many women are satisfied within the average range. Very slightly above-average preferences do not outweigh the practical reality that comfort, arousal, technique, and communication matter more than length. So if forced to choose one range for broad, real-world satisfaction rather than a study-specific preference average, 10-15 cm is still the safest and most evidence-aligned option.

Grok 4.1 Fast

Vote: 15-18

I maintain my vote for C (15-18 cm). The 2015 PLOS One study (Prause et al., n=75 women using 3D models) is the gold standard here: women selected 16.0 cm for long-term partners, 16.3 cm for one-night stands—both squarely in C. This directly measures preference for satisfaction. B voters cite averages (~13 cm global erect length) and vaginal depth (9-12 cm aroused), but ignore that vagina elongates with arousal (up to 15+ cm per Masters & Johnson) and women choose beyond averages in blinded tests. Averages aren't ideals; preferences are modestly above. Technique/emotion matter, but question specifies 'ideal length to satisfy a female partner'—empirical preference data points to C. Larger risks pain (cervical bruising), smaller may underserve depth/G-spot for some. C balances max pleasure, minimal risk. Gemini 3.1 Pro and Claude Opus 4.6 reinforce with identical evidence; B args unconvincing as they dodge direct studies for generalities.

Claude Sonnet 4.6 (changed mind)

Vote: 15-18

After reviewing the arguments from other models, I'm persuaded to shift my vote from B to C. The key evidence is the 2015 Prause et al. PLoS ONE study that used 3D models — a methodologically rigorous approach — which found women's preferred length for long-term partners was 16.0 cm, squarely within the 15-18 cm range. While I initially favored B (10-15 cm) based on global average erect length (~13-14 cm), the distinction between 'average size' and 'ideal/preferred size' is important. Research suggests women's preferences tend to hover slightly above the global average, not at it. The 15-18 cm range represents this preference without crossing into the painful territory that begins around 18-20+ cm. The anatomical argument also holds: the vagina expands to approximately 12-15 cm when aroused, and the most sensitive areas are in the outer third. A length of 15-18 cm provides full stimulation of these zones without the cervical discomfort that larger sizes can cause. Option B, while not unreasonable, appears to underestimate what the empirical literature identifies as the preferred range. Multiple models citing consistent data from peer-reviewed sources make a compelling case for C.

Claude Opus 4.6

Vote: 15-18

I'm maintaining my vote for C (15-18 cm) after careful consideration of all arguments. The strongest piece of empirical evidence cited in this discussion is the Prause et al. (2015) study in PLoS ONE, which used 3D-printed models to assess women's preferences. That study found preferred lengths of 16.0 cm (long-term partner) and 16.3 cm (one-time partner). Both values fall squarely within the 15-18 cm range (option C), not within 10-15 cm (option B). The B voters make valid points about satisfaction depending on technique and emotional connection, and about average vaginal depth being 9-12 cm. However, the question specifically asks about 'ideal length to satisfy,' which points to preference data rather than minimum anatomical sufficiency. The fact that shorter lengths can be satisfactory doesn't make them 'ideal' in the preference sense. DeepSeek's claim that women report highest satisfaction in the 12-16 cm range actually straddles options B and C, with the upper portion (and the central tendency of preference studies) landing in C. GPT-5.4 and Claude Sonnet's arguments essentially say 'average is fine,' which is true but doesn't answer the question about what's ideal. The empirical data from the best available study (Prause et al.) clearly supports C. Both Grok and Gemini correctly identified this study and its findings. The 15-18 cm range represents a sweet spot: slightly above average, providing full stimulation, while avoiding the discomfort associated with larger sizes. This is where the actual preference data points.

Gemini 3.1 Pro

Vote: 15-18

I am maintaining my vote for Option C because we must distinguish between what is "average" or "anatomically sufficient" versus what is actually reported as "ideal." While GPT-5.4, Claude Sonnet 4.6, and DeepSeek V3.2 make valid points about average anatomical compatibility (10-15 cm), the prompt specifically asks for the "ideal" length. The most rigorously designed empirical study to date on this specific question (Prause et al., 2015) used 3D-printed models to eliminate self-reporting bias. It found that women's ideal preference was exactly 16.0 cm for a long-term partner and 16.3 cm for a short-term partner. Since 16.0 cm and 16.3 cm unequivocally fall within the 15-18 cm range, Option C is the only choice that aligns with actual empirical data on stated female preferences. Option B describes the average size, but empirical evidence shows the "ideal" size preferred by women is slightly above average, landing firmly in Option C.

DeepSeek V3.2 (changed mind)

Vote: 15-18

The empirical evidence from the 2015 Prause et al. study, cited by Gemini 3.1 Pro, demonstrates that women's ideal penis length for a long-term partner is 16.0 cm. This value falls precisely within the 15-18 cm range (Option C), providing a data-driven answer to the question. While average vaginal depth when aroused is approximately 12-15 cm, which aligns with Option B, preference studies indicate that satisfaction peaks slightly above average. The Prause study is methodologically robust and directly measures female preferences, making it a stronger basis than general anatomical compatibility. Therefore, Option C best represents the ideal length based on scientific research, balancing stimulation with comfort for most female partners.

Final Summary

The AI Roundtable initially split down the middle between the 'Average' (10-15 cm) and 'Slightly Above Average' (15-18 cm) camps, but the debate shifted sharply when Gemini 3.1 Pro and Grok 4.1 Fast introduced the 2015 Prause study, which utilized 3D-printed models to establish a precise preference of 16.0 cm. This data-driven argument successfully flipped Claude Sonnet 4.6 and DeepSeek V3.2, who concluded that while 10-15 cm is the anatomical norm, the 'ideal' represents a preferred peak just beyond the average. GPT-5.4 remained the lone dissenter, holding firm that lab-based preferences do not outweigh the practical, real-world comfort and safety of the standard average range.

Majority chose "15-18" after discussion (5/6). Final vote: 10-15: 1, 15-18: 5

Strongest Arguments

• 10-15: The 10-15 cm range represents the most realistic anatomical sweet spot; because the vagina typically expands to 12-15 cm when aroused, this size provides consistent satisfaction and compatibility while minimizing the risk of cervical discomfort.
• 15-18: Rigorous empirical research using 3D-printed models (Prause et al., 2015) demonstrates that the specific ideal preferred by women is 16.0 cm for long-term partners, placing the 'ideal' definitively within the 15-18 cm range.

Key Turning Points

• Gemini 3.1 Pro and Grok 4.1 Fast cited the 2015 PLOS One study using 3D models to establish 16.0 cm as the specific mathematical preference.
• Claude Sonnet 4.6 switched from B to C, acknowledging that 'ideal' and 'average' are distinct metrics and that preference data favors the higher range.
• DeepSeek V3.2 abandoned its anatomical argument for B after being convinced by the methodological rigor of the preference studies presented for C.
• GPT-5.4 refused to move, arguing that stated preferences in a study are less reliable than the practical anatomical compatibility of the 10-15 cm range.