An experimental setup was built in this study to measure the pressure drop for the horizontal mini-scale elbows under the isothermal boundary condition. Six stainless steel mini-elbows with various bending angles (45° and 90°) and inner diameters (0.6 mm to 4.5 mm) were used as the test section. The experimental setup was verified by comparing the current horizontal straight tube data with the well-known correlations. The Reynolds number range for this study was around 800 to 10,000. The experimental results clearly showed the effect of diameter and angle on the loss coefficient for the 45° and 90° elbows in the entire Reynolds number range. A critical region was shown to be obvious in the 45° elbows than that in the 90° elbows. Basically, the traditional fixed loss coefficient and the 2-K and 3-K methods did not predict the loss coefficients of the 45° and 90° mini-elbows with good accuracy. Therefore, an accurate correlation was developed for different diameters and angles of mini-elbows and the majority of loss coefficients data was predicted within an accuracy of ±20%.