Measuring Stretched Penile Length
Measure stretched penile length from the pubic bone to the tip of the glans (BTT method) using a rigid ruler while applying firm traction to the flaccid penis in a temperature-controlled environment. 1
Proper Measurement Technique
Patient Positioning and Environment
- Conduct measurements in a private, temperature-controlled room at 21°C (72°F) to ensure consistent conditions 1, 2
- Have the patient stand upright or lie supine with the penis in a horizontal position 1
Measurement Method
- Use the pubic bone-to-tip (BTT) technique rather than skin-to-tip (STT) measurement, as BTT is significantly more accurate and reliable, particularly in overweight patients 1
- Apply firm traction to the flaccid penis using a rigid ruler or tape measure 3, 4
- Measure from the pubic bone (pressing the ruler firmly against the pubic symphysis) to the distal tip of the glans 1
- Apply approximately 450 grams of tension force during stretching to reach the potential erection length 5
Clinical Context and Accuracy
Correlation with Erect Length
- Stretched penile length correlates 80.2% with erect length, making it the most accurate non-invasive predictor 4
- However, stretched measurements typically underestimate erect length by approximately 20% (mean 2.64 cm) 1, 2
- The predictability of erect length using stretched measurements is 65.3% accurate 4
Important Considerations for Special Populations
- In patients with erectile dysfunction, expect shorter stretched lengths (mean 11.2 cm vs 12.9 cm in potent men) 3
- In patients with Peyronie's disease, perform measurements during office intracavernosal injection (ICI) testing with the penis in the erect state to accurately document curvature and deformities 6, 7, 8
- For patients with significant suprapubic fat, the BTT method is essential as it accounts for adipose tissue that obscures true penile length 1
Critical Pitfalls to Avoid
Measurement Errors
- Do not measure from the penopubic skin junction, as this significantly underestimates true penile length, especially in overweight patients 1
- Do not rely on flaccid (non-stretched) measurements, which have only 50.8% accuracy in predicting erect length and correlate poorly (71.2%) with erect size 4
- Be aware that interobserver variability ranges from 16-27%, so ideally the same clinician should perform serial measurements 2
Insufficient Traction
- Ensure adequate stretching force (approximately 450 grams) is applied, as most clinicians apply significantly less force than required to approximate erect length 5
- Insufficient traction will result in underestimation of potential erect length 5
Patient Comfort and Privacy
- Always ensure patient privacy and explain the procedure beforehand to reduce anxiety 6
- For patients with performance anxiety or psychogenic erectile dysfunction, consider that the presence of morning or nocturnal erections suggests adequate physiologic function 6
When to Use Alternative Measurement Methods
- For patients being evaluated for penile augmentation or small penis anxiety, erect measurements obtained via intracavernosal injection are preferred over stretched measurements due to the 20% underestimation with stretching 2
- For surgical planning in Peyronie's disease, perform measurements during pharmacologically-induced erection to accurately assess curvature and deformity 6, 8