Overview

IV flow rate is computed from the prescribed volume and infusion time, with the unit set by the delivery method. An infusion pump is programmed in mL/hr (volume ÷ time in hours), so no drop factor is needed. A gravity (manual) drip with no pump is counted in gtt/min and DOES require the tubing's drop factor. Always confirm the calculated rate against the actual order before starting.

Interpretation

Pick the formula by delivery method, then read the drop factor off the tubing package. Macrodrip tubing (10, 15, or 20 gtt/mL) is for routine/rapid infusions; microdrip tubing (60 gtt/mL) is for precise, low-volume infusions. Because microdrip is 60 gtt/mL and there are 60 min/hr, microdrip gtt/min equals mL/hr.

Pump (mL/hr) vs gravity drip (gtt/min)

Infusion pumpGravity drip

Unit setmL/hrgtt/min

Formulavolume mL / time hrvolume mL x drop factor / time min

Drop factor neededNoYes (off tubing)

Time unitHoursMinutes

Worked example1,000 mL / 8 hr = 125 mL/hr1,000 mL x 15 / 480 min = 31 gtt/min

Infusion pump

Unit set: mL/hr
Formula: volume mL / time hr
Drop factor needed: No
Time unit: Hours
Worked example: 1,000 mL / 8 hr = 125 mL/hr

Gravity drip

Unit set: gtt/min
Formula: volume mL x drop factor / time min
Drop factor needed: Yes (off tubing)
Time unit: Minutes
Worked example: 1,000 mL x 15 / 480 min = 31 gtt/min

Technique

Worked calculation sequence

Read order: volume + time1,000 mL over 8 hr
Pump path: mL / hr1,000 / 8 = 125 mL/hr
Drip path: convert hr to min8 hr x 60 = 480 min
Drip path: vol x drop factor / min1,000 x 15 / 480 = 31.25
Round drip to whole drop= 31 gtt/min

During — Monitoring

Time-tape gravity bags

mark expected level by the hour to catch drift

Recount gravity drip hourly

manual drips change with position, height, and patency

Verify pump-programmed rate

confirm displayed mL/hr matches the order

Assess IV site patency

infiltration/occlusion alters actual delivery

Patient Teaching

Do not adjust the roller clamp

patient should not speed up or slow the gravity drip

Report swelling or pain at site

early sign of infiltration

Avoid kinking or lying on tubing

obstructs flow and triggers alarms

Call for pump alarms

do not silence; notify the nurse

Report Nowescalate immediately

Free-flowing IV Hallmark

uncontrolled gravity flow; clamp and reassess immediately

Rate mismatch with order

stop, recalculate, and correct before continuing

Fluid overload signs

dyspnea, crackles, new edema from too-fast rate; slow/stop and notify

Wrong-unit calculation

gtt/min entered as mL/hr or omitted drop factor causes large dosing error

Clinical Pearl

Pump = mL/hr (volume over hours, no drop factor); gravity drip = gtt/min (volume x drop factor over minutes). Microdrip is 60 gtt/mL, so its gtt/min equals mL/hr.