Drop Factor Science — Macrodrip vs. Microdrip

The drop factor is the number of drops required to deliver exactly 1 mL of fluid. It is determined by the size of the drip orifice inside the drip chamber of the tubing set. Understanding drop factors is foundational to safe, accurate gravity infusion delivery.

Macrodrip sets (10 gtt/mL and 15 gtt/mL) deliver larger drops of fluid. Fewer drops per minute are required to achieve a given flow rate, making them suitable for moderate-to-high volume infusions in adult non-acute settings. The 10 gtt/mL set delivers the fewest, largest drops — resulting in the lowest drop count per minute for any given flow rate. The 15 gtt/mL set delivers slightly smaller drops, requiring a higher count but offering finer manual control.

Microdrip sets (60 gtt/mL) deliver very small drops — 60 drops per mL. Because each mL is divided into many small drops, the clinician has much finer control over the infusion rate without using an electronic pump. Microdrip sets are the preferred choice when precision is critical: low-volume infusions, pediatric patients, neonatal patients, and patients with limited fluid tolerance.

Clinical selection guidance: Use 10 gtt/mL when infusing larger volumes (500-1000 mL) at moderate rates and you want to minimize drop counting time. Use 15 gtt/mL as a versatile all-purpose set — it balances count simplicity with adjustment precision. Use 60 gtt/mL for any infusion under 100 mL/hr, for slow medication drips, or when working with pediatric or fluid-sensitive patients.

Important: the drop factor is printed on every Bridge administration set package. Always verify the drop factor before calculating drip rates. Using the wrong drop factor in your calculation will result in incorrect infusion delivery — a preventable clinical error.