The aim of the present study was to determine the reliability and differences between three fascicle length (FL) estimation methods when utilizing a 10-cm ultrasound (US) probe. Thirteen males (24.1 ± 3.8 years, 79.3 ± 14 kg, 179 ± 6.6 cm) participated. Bicep femoris long head (BFLH) US images were collected on two separate occasions. Three previously established extrapolation methods were utilized. Near-perfect reliability was observed for all methods. Criterion estimation resulted in a significant, trivial (p = 0.016,g = 0.17) increase in FL compared to the basic trigonometry equation with non-significant, trivial increase (p = 0.081,g = 0.10) between the criterion and partial measure method. The partial measure method was not significantly or meaningfully greater than the basic trigonometry method (p = 0.286,g = 0.08). Both alternative methods demonstrated unacceptable LOA (>5%), with heteroscedasticity. All methods of extrapolation are reliable and could be used over time. However, as methods are not comparable, there could be a rationale to utilize underestimated results to ensure a degree of cushioning.